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Title: Biology AS Level OCR A Revision Notes (full AS course - new spec for 2017)
Description: Full AS course for OCR Biology A - Revision Notes (new spec) with diagrams :)
Description: Full AS course for OCR Biology A - Revision Notes (new spec) with diagrams :)
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Biology AS Level Notes
Cell Structure 2
...
Magnification - number of times larger an image appears, compared with the size of
the image
...
Photomicrograph - photograph of an image seen using an optical microscope
...
Microscopes produce linear magnification
...
Optical light microscopes played a key role in our understanding of cell structure
...
They allow magnification up to x1500/x2000
...
However, their resolution is limited
so they cannot magnify any higher while still giving a clear image
...
Structures closer together than 200nm will appear as one object
...
Laser scanning microscopes / confocal microscopes:
use laser light to scan object point by point and assemble the pixel information into
one image, displayed on a screen
high resolution and show high contrast
depth selectivity, can focus on structures at different depths, therefore can be used to
observe whole living specimens as well as cells
used in the medical profession to give effective treatment
also used in many branches of biological research
Electron microscopes use a beam of fast-travelling electrons with a wavelength of 0
...
They have a much greater resolution than optical microscopes and can be used to give clear
and highly magnified images
...
Transmission electron microscopes:
specimen must be chemically fixed (dehydrated and stained)
beam of electrons passes through specimen; some pass through and are focused on the
screen
the electrons form a 2D black and white image (electron micrograph)
can produce magnification of up to 2 million
times
Scanning electron microscopes were developed in the
1960s
...
This gives a 3D image with a magnification from x15
to x200,000
...
The specimen still
must be placed in a vacuum and is often coated with a
fine film of metal
...
You can use an optical microscope to view specimens
including:
living organisms such as Paramecium and
Amoeba
smear preparations of human blood and cheek cells
thin sections of animal, plant, fungal tissues such as bone, muscle, leaf, root, fungal
hyphae
Many biological structures are colourless and transparent
...
Some use
a dark background against which the illuminated specimen shows up
...
Stains are coloured chemicals that bind to molecules, making the specimen easy to see
...
This is called
differential staining
...
Focus the specimen under low
power
...
Use a title that explains what the drawing is and the magnification used
...
Make a low-power plan to show where the different tissues are and do not draw
individual cells
...
Label the plan
...
Draw clear unbroken lines and do not shade
...
Use a ruler to draw label lines
...
Stage graticule - precise measuring device; a small scale placed on a microscope stage
and used to calibrate the value of eyepiece divisions at different magnifications
...
As the specimen is viewed, the eyepiece graticule scale is placed on it and the
dimensions of the specimen can be measured in eyepiece units
...
It changes size at different magnifications
...
The ruler is 1mm long and divided into 100 divisions
...
01mm or 10
micrometres
...
Bring the stage graticule into focus using a low power (x4) objective
...
Check the value of one eyepiece division at this magnification
(x40)
...
Repeat with different magnifications of the objective lens
...
Place two drops of iodine on to them and add the coverslip
...
Use low power and then higher power
...
Animal, plant, fungal and protoctist cells are eukaryotic
...
This provides a division of labour so every cell can
carry out its functions efficiently
...
Name
Nucleus
Nuclear
envelope
Nucleolus
Cytoplasm
Cytoskeleton
Plasma
membrane
Vesicles
Ribosomes
Description
Surrounded by a double
membrane – nuclear
envelope
...
No membrane
...
Jelly-like substance
...
Consists of:
microfilaments made of
actin, intermediate
filaments, microtubules
made of tubulin, and
cytoskeletal motor
proteins
...
Membrane at the cell
surface
...
Made of ribosomal RNA
in the nucleolus as 2
Function
Control centre of the cell
...
Transmits genetic info
...
Separates nucleus from rest of cell
...
Pores allow
mRNA to leave the nucleus
...
Chromosomes
contain the organism’s genes
...
Microfilaments: give support and mechanical
strength, keep cell’s shape stable and allow
cell movement
...
Microtubules provide shape and support to
cells and help substances and organelles
move through the cytoplasm
...
Also form a spindle before a
cell divides
...
Controls what enters and exits the cell
...
When bound to the RER, are for synthesising
proteins that will be exported outside the cell
...
Some
remain free in the
cytoplasm and some attach
to the RER
...
Mitochondria
Surrounded by 2
membranes
...
Golgi
apparatus
Stack of membrane-bound
flattened sacs
...
RER
System of membranes
containing cisternae that
are continuous with the
nuclear membrane
...
SER
System of membranes
containing cisternae that
are continuous with the
nuclear membrane
...
Lysosomes
Small bags formed by the
Golgi apparatus
...
Contain
powerful digestive
enzymes
...
Protrusions from the cell,
surrounded by the cell
surface membrane
...
Formed from centrioles
...
Forms spindle fibres for cell division
...
Involved in the
formation of cilia
...
Self-replicating so more can be
made if energy needs increase
...
Proteins are modified, e
...
adding sugar/lipid
molecules
...
Intracellular transport system
...
Provides large
surface area for ribosomes, which assemble
amino acids into proteins
...
Contains enzymes that catalyse reactions
involved with lipid metabolism such as:
Synthesis of cholesterol, lipids/phospholipids
and steroid hormones
...
Keep the powerful hydrolytic enzymes
separate from the rest of the cell
...
Beat and move the band of mucus in airways
...
Sperm have an undulipodium
to enable them to move
...
Maintains cell
stability, as when full it pushes against the
Chloroplasts
Cellulose cell
wall
tonoplast and contains
fluid
...
Inner
membrane is continuous
with stacks of flattened
membrane sacs called
thylakoids that contain
chlorophyll
...
Fluid filled matrix
is called the stroma
...
On the outside of the
plasma membrane
...
cell wall making the cell turgid
...
Site of photosynthesis
...
Water is split to supply hydrogen ions
...
Abundant in leaf cells
...
Provides strength and
support, maintains cell shape, contributes to
strength + support of whole plant
...
Making and secreting a protein:
the gene with coded instructions for a protein (e
...
insulin) on chromatin in the
nucleus is transcribed on to mRNA
many copies of this mRNA are made and pass out of the pores in the nuclear envelope
to the ribosomes
at the ribosomes, the instructions are translated and insulin molecules are assembled
the insulin molecules pass into the cisternae of the RER and along the hollow sacs
vesicles with insulin inside are pinched off the RER and pass via microtubules and
motor proteins to the Golgi apparatus
the vesicles fuse with the Golgi apparatus where the insulin protein molecules may be
modified for release
inside vesicles pinched from the Golgi apparatus, these molecules pass to the plasma
membrane
the vesicles and plasma membrane fuse and the insulin is released outside the cell
...
Bacteria have prokaryotic cells:
flagella - long projections allowing bacteria to move
cytoplasm
ribosome
pili - small hair-like projections that allow passage of plasmid DNA from one cell to
another
plasmids - small loops of DNA
nucleoid - area within cytoplasm where DNA is positioned
capsule - protective waxy capsule surrounding cell wall
cell wall (peptidoglycan)
plasma membrane
Similarities to eukaryotic cells:
plasma membrane
cytoplasm
DNA and RNA
ribosomes for assembling proteins
Differences to eukaryotic cells:
much smaller
less well-developed cytoskeleton with no centrioles
no nucleus
no membrane-bound organelles
peptidoglycan wall instead of cellulose
smaller ribosomes
naked DNA that floats freely in cytoplasm as a loop (not linear chromosomes)
Prokaryotic cells divide by binary fission and not by mitosis because they do not have linear
chromosomes
...
Molecular and biochemical evidence indicates that eukaryotic cells evolved from prokaryotic
cells around 2 billion years ago when some prokaryotic cells with infolded membranes
invaded or were engulfed by other prokaryotes but not digested
...
Both chloroplasts and
mitochondria share characteristics with prokaryotic cells:
small ribosomes
loops of DNA
contain RNA
can divide by binary fission
This theory is called the endosymbiont theory
...
2
Condensation reaction - reaction that occurs when two molecules are joined with the
removal of water
...
Hydrolysis reaction - reaction that occurs when a molecule is split into two smaller
molecules with the addition of water
...
Polymer - large molecules made from monomers
...
Carbon has 4 electrons, so
by sharing electrons with other atoms the outer shell can be filled and it becomes strongly
bonded with the other atom
...
Carbon forms 4
covalent bonds
...
A condensation reaction occurs when two molecules are joined with the removal of water
...
Condensation
reactions happen when two OH groups react together
...
The units joined together are called
monomers
...
Water consists of two H atoms
covalently bonded to one O atom
...
This means the oxygen atom
becomes slightly negative and the hydrogen atoms become slightly positive
...
A hydrogen bond is a weak interaction which happens wherever molecules contain a slightly
negatively charged atom bonded to a slightly positively charged hydrogen atom
...
Properties of water:
liquid
density
solvent
cohesion and surface tension
high specific heat capacity
high latent heat of vaporisation
reactant
As a liquid, water molecules constantly move around, making and breaking H bonds
...
Because it is a liquid at
room temperature, water can:
provide habitat for living things in rivers, lakes, seas
form a major component of tissue in living organisms
provide a reaction medium
provide an effective transport medium e
...
blood
If water was less dense, aquatic organisms would find it hard to float
...
If water did this, water at the top of a pond would freeze and sink
...
However, water only
gets denser as it gets colder until about 4°C
...
Because ice is less dense than
water:
aquatic organisms have a stable environment to live in through winter
bodies of water insulated against extreme cold by the layer of ice reducing the rate of
heat loss
Water is a good solvent for many substances in living things
...
As water is polar, the positive and
negative parts are attracted to the negative and positive parts of the solute
...
They dissolve and a solution is formed
...
The water
molecules demonstrate cohesion
...
This means the surface of the water contracts and gives the surface of water an ability to
resist force applied to it
...
Because of cohesion and surface
tension:
columns of water in plant vascular tissue are pulled up the xylem
insects like pond-skaters can walk on water
Water temperature is a measure of the kinetic energy of the molecules
...
Therefore, a lot of heat energy has to be put in to
increase the kinetic energy and temperature
...
This means water does not heat up or cool down quickly
...
Because the molecules are held
together by H bonds, a large amount of energy is needed for water to evaporate
...
E
...
mammals are cooled
when sweat evaporates
...
This is not due to its polarity, but its role as a reactant is important for digestion
and synthesis of large biological molecules
...
Glycosidic bond - a bond formed between two monosaccharides by a condensation
reaction
...
g
...
g
...
g
...
Some carbohydrates are part of other
molecules such as nucleic acids
...
Monosaccharides are the simplest carbohydrates
...
They have many carbon-hydrogen bonds
...
They can exist as straight chains or in ring or
cyclic forms
...
Different sugars have different numbers of
carbon atoms (i
...
hexose has 6, pentose 5 etc
...
In solution, triose and tetrose sugars exist as straight chains, however pentoses and hexoses
are more likely to be found in a ring or cyclic form
...
Like monosaccharides, disaccharides are sweet and soluble
...
Maltose and lactose are reducing sugars whereas sucrose is a nonreducing sugar
...
There are lots of combinations that
determine the disaccharide made:
alpha glucose + alpha glucose --> maltose
alpha glucose + fructose --> sucrose
alpha glucose + beta galactose -->
lactose
beta glucose + beta glucose -->
cellobiose
When they join, a condensation reaction
occurs to form a glycosidic bond
...
The water
provides a hydroxyl (OH) group, and a
hydrogen (H) which help break the
glycosidic bond
...
g
...
Those made of more than one are called heteropolysaccharides, e
...
hyaluronic
acid
...
The energy released is used to
make ATP
...
Plants store
energy as starch in chloroplasts and starch grains, and humans store energy as glycogen in
muscle and liver cells
...
They form good stores of monosaccharides for the following reasons:
glycogen and starch are compact so do not occupy a large amount of space
glucose molecules are in chains so can easily be 'snipped off' by hydrolysis when
required for respiration
...
It is a long chain of alpha glucose molecules
...
It coils into a spiral shape with hydrogen bonds holding the
spiral in place
...
Amylopectin is also found in plants, and like amylose has glycosidic bonds between carbons
1 and 4, but also has branches formed by glycosidic bonds between carbons 1 and 6
...
Glycogen is found in animals
...
The 1-4 bonded
chains tend to be small so glycogen has less tendency to coil
...
It is easier to remove monomer units as there are more
ends
...
It's a tough, insoluble and
fibrous homopolysaccharide made from chains of up to 15,000 beta glucose molecules
bonded through condensation reactions to form glycosidic bonds
...
This is a result of bonding
...
This and the beta 1-4
glycosidic bond help prevent the chain spiralling
...
The hydroxyl group on carbon 2 sticks out, enabling H bonds to form between chains
...
These bundle together to form macrofibrils containing up to 400 microfibrils,
which are embedded in pectins to form plant cell walls
...
Cellulose is good for plant cell walls because:
microfibrils and macrofibrils have high tensile strength because of the strength of the
glycosidic bonds and the hydrogen bonds between chains
macrofibrils run in all directions crossing the wall for extra strength
it is difficult to digest cellulose because the glycosidic bonds are hard to break; most
animals do not have an enzyme to catalyse the reaction
Key features of cell wall:
because plants don't have a skeleton, each cell needs strength to support the plant
there is space between macrofibrils for water and mineral ions to pass on their way
into/out of the cell, making the cell wall fully permeable
the wall has high tensile strength which prevents plant cells bursting when turgid,
helping to support the plant; turgid cells press against each other, supporting the
structure of the plant
the wall protects the delicate cell membrane
the macrofibril structure can be reinforced with other substances for extra support or
to make it waterproof, e
...
cutin, suberin, lignin
...
Cotton is 90% cellulose, and
cellophane and celluloid are also derived from it
...
Bacteria also have cell walls but they are not made of cellulose
...
Insects and crustacean exoskeletons are made of chitin
...
It forms cross-links between
long parallel chains of acetylglucosamine
...
Macromolecule - a very large, organic molecule
...
Lipids contain large amounts of C an H and smaller amounts of O
...
The three most important lipids are triglycerides, phospholipids and
steroids
...
Glycerol has three carbon atoms
...
Glycerol --->
Fatty acids have a carboxyl group (COOH) on one end, attached to a hydrocarbon tail
...
The carboxyl group ionises into H+ and a
COO- group
...
If a fatty acid is saturated, there are no C=C bonds
...
A single C=C bond makes a fatty acid monounsaturated; more
than one makes it polyunsaturated
...
These kinks push the
molecules apart slightly so makes them more fluid
...
If there are more unsaturated, the melting point is lower
...
A
condensation reaction happens between the COOH group and the OH
group
...
A water molecule is produced and the covalent bond formed is called an ester bond
...
The ester bonds are hydrolysed, then both glycerol and fatty acids can be
broken down to carbon dioxide and water
...
Insulation - Adipose tissue is a storage location for lipid in whales, acting as a heat
insulator
...
Buoyancy - Fat is less dense than water so is used by aquatic mammals to help them
stay afloat
...
Phospholipids have the same structure as triglycerides
except one of the fatty acids is replaced by a phosphate
group
...
Commonly one of the chains on a phospholipid is saturated
and one unsaturated
...
However, the fatty acid
chains are non-polar and repelled by water
...
This makes the phospholipid amphipathic
...
Amphipathic phospholipids form a layer on the surface of water with heads in the water and
tails sticking out of the water
...
Amphipathic phospholipids form membranes around cells and organelles
...
The phospholipids form a bilayer with two rows of
phospholipids, tails pointing in
...
This gives the membrane
some stability
...
It is only possible for small and non-polar
molecules to move through the tails such as oxygen and carbon dioxide
...
Cholesterol is a sterol (steroid alcohol) - a type of lipid not made of glycerol and fatty acids
...
It is a small, hydrophobic molecule,
meaning it can sit in the middle of the hydrophobic part of the bilayer
...
It is mainly made in the liver in animals
...
The steroid hormones testosterone, oestrogen and vitamin D are made of cholesterol
...
Amino acids - monomers of all proteins; all have the same basic structure
...
Proteins are large polymers consisting of long chains of amino acids
...
g
...
Animals can make some amino acids
but must ingest others (essential amino acids)
...
Each amino acid contains C, H, O and N
...
There are over 500 different amino acids but only
20 are proteinogenic (formed in proteins)
...
The R group
stands for a different element in each amino acid
...
Amino acids can act as buffers
...
The amino group can accept a H + ion to change from NH2 to NH3+
...
The carboxyl group can give up a H + ion to change from COOH to COO-
...
At low pH, (lots of H+) the amino acid will accept H + ions
...
This means an amino acid has acidic and basic properties and is known as amphoteric
...
Amino acids can help regulate the
changes in pH
...
A buffer is a substance which helps resist changes
to pH
...
Making a peptide
bond involves a condensation reaction and breaking one involves hydrolysis
...
Protease enzymes in the intestines break peptide bonds during
digestion
...
All amino acids join in the same way, whatever R group they have
...
Joining a longer chain of amino acids together forms a polypeptide
...
Primary structure - the sequence of amino acids found in a molecule
...
The main forms
are the helix and pleated sheet
...
Its shape arises due to
interactions including H bonding, disulphide bridges, ionic bonds and hydrophobic
interactions
...
Primary Structure:
The sequence of amino acids in a protein chain is called primary structure
...
The number and order of
amino acids in a protein chain is important, as changing just one amino acid can alter the
function of the protein
...
The
function of a protein is determined by its structure
...
Secondary Structure:
The chain of amino acids twists into a shape called secondary
structure
...
The helix is held together by H
bonds between the NH group of one amino acid and the CO group
of another
...
When one
chain folds over on itself, it forms a beta-pleated sheet
...
Although H bonds are weak, when many are formed it
makes both structures stable at optimal temperature and
pH
...
Tertiary Structure:
When these coils and pleats start to fold themselves, along with areas of straight chains of
amino acids, tertiary structure forms
...
It may adopt a supercoiled shape
(fibrous) or a spherical shape (globular)
...
This may be held together with the same bonds that hold tertiary structure together
...
In amino acids, these form in hydroxyl, carboxyl and amino
groups
...
They may also form between polar areas of the R groups on different amino acids
...
Multiple H bonds can give protein molecules a lot of strength
...
These
ionise into NH3+ and COO groups
...
The R group of cysteine contains sulphur
...
These are strong covalent bonds
...
Hydrophilic parts are found at the edge, close to the water
...
Fibrous protein - has a long, thin structure, insoluble in water and metabolically
inactive, often having a structural role within an organism
...
Prosthetic group - a non-protein component that forms a permanent part of a
functioning protein molecule
...
These features enable them to form fibres, which tend to have a structural
function, e
...
collagen and elastin in connective tissue
...
Any hydrophobic R groups
are turned inwards towards the centre of the molecule, while hydrophilic groups are
on the outside
...
They often have very specific shapes, helping
them to take up roles as enzymes, hormones, haemoglobin etc
...
Tendons are made of collagen and connect muscles to bones, allowing them to pull on
bones
...
Cartilage and connective tissue are made from collagen
...
Alongside H bonding, this makes the molecule very strong
...
It provides mechanical
protection and an impermeable barrier to infection and, being waterproof, prevents entry of
water-borne pollutants
...
It's found in living things
where they need to stretch or adapt their shape
...
Elastin is also in lungs to allow them to inflate and deflate, and in
the bladder to help it expand to hold urine
...
The quaternary structure of haemoglobin is made of four polypeptides: two alpha globin
chains and two beta globin chains
...
The interactions between the polypeptides
give the molecule a very specific shape
...
These are prosthetic groups, an essential part of the molecule, without which it could not
function
...
The haem group contains an iron ion
...
The function of haemoglobin is to carry oxygen from the lungs to the tissues
...
When it binds,
haemoglobin turns from purple-red to bright red
...
Insulin is made of two polypeptide chains
...
Both chains fold into a tertiary structure and
are then joined by disulphide links
...
Insulin binds to glycoprotein receptors on
the outside of muscle and fat cells to increase their uptake of glucose from the blood and
increase their rate of consumption of glucose
...
The enzyme is made up of a single
polypeptide chain of 327 amino acids but folds into tertiary structure
...
This shows why it is stable
in the stomach (acidic environment)
...
The tertiary structure is also held
together by H bonds and two disulphide bridges
...
As techniques
developed, predictions for secondary structure were based on the probability of an amino acid
or sequence of amino acids being in a particular secondary structure
...
There can
be multiple solutions to the same amino acid sequence, and other methods sometimes
need to be applied to reduce the number of solutions
...
Inorganic ions are essential for key biological processes:
Calcium (Ca2+)
increases bone, tooth, cartilage rigidity, component of
exoskeleton in crustaceans
important in clotting blood and muscle contraction
activator for several enzymes
stimulates muscle contraction, regulates nerve impulse
transmission
regulates permeability of cell membranes
important for cell wall development in plants
Sodium (Na+)
Potassium (K+)
Hydrogen (H+)
Ammonium
(NH4+)
Nitrate (NO3-)
Hydrogencarbonate
(HCO3-)
Chloride (Cl-)
Phosphate (PO43-)
Hydroxide (OH-)
involved in regulation of osmotic pressure, control of water
levels in body fluid and pH maintenance
affects carb
...
Deficiency symptoms can occur if ions are not consumed,
e
...
cobalt deficiency causes anaemia
...
If starch is present, there will
be a colour change from yellow-brown to blue-black
...
This
causes the colour change
...
They are called
reducing sugars because they can reduce (give electrons to) other molecules
...
Benedict's contains Cu2+ ions which are reduced to Cu+ ions, forming orangered copper oxide (Cu2O)
...
If you use Benedict's in excess, the intensity of the red colour is proportional to the
concentration of sugar
...
It is also possible to use commercially manufactured test strips to test for reducing sugars
...
These are often used to test the urine of diabetics
...
Test a sample for reducing sugars first to check there are none
...
Cool the solution and use sodium hydrogencarbonate solution to neutralise it
...
A positive (green-yellow-orange-red) result shows that non-reducing sugars were present
...
If you have a
positive test for reducing sugars from your first sample, you can go on to test for nonreducing sugars
...
You can extract the precipitate from the
mixture by filtration
...
Any lipid will go into solution
...
A cloudy white emulsion indicates presence of lipids
...
To test for proteins, use a biuret test
...
The colour is formed by a complex between the nitrogen atoms in a peptide chain and
Cu2+ ions, which is why this test actually detects the presence of peptide bonds
...
If there is more sugar present:
the amount of precipitate will increase
the amount of copper (II) ions remaining in solution will decrease
You can use colorimetry to quantify the concentration of sugar in the original sample
...
A centrifuge is used to separate the precipitate and any excess Benedict's solution (the
supernatant)
...
Fingerprints can affect light transmission
...
g
...
When using a colorimeter, the device is reset between readings by using a 'blank'
sample (water) to set transmission to 100%
...
1
...
2
...
3
...
4
...
This provides a calibration curve, which can be used with
other unknown samples to determine the sugar concentration
...
They can be used to detect
contaminants in water, and
pathogens and toxins in
food
...
g
...
There are two components to chromatography:
The stationary phase is either the paper or thin layer chromatography (TLC) plate
...
In both cases, there are free OH groups pointing outwards, in
contact with the mobile phase
...
Water is used for polar molecules and ethanol for
non-polar molecules
...
Set-up:
Draw a pencil line with a tiny dot to show where to place the solution
...
When dry, lower it into the solvent
...
Cover the beaker with a watch glass
...
Remove it from the solvent and lay it out to dry
...
You
can use relative distances travelled to help identify the pigments
...
Sometimes with colourless molecules, you must use:
UV light - TLC plates have a chemical that fluoresces under UV light
...
Ninhydrin - This binds to amino acids which are then visible as brown or purple
spots
...
The speed at which molecules move along the paper depends on their solubility in the solvent
and their polarity
...
Exposed OH groups make the surface of the paper polar, allowing it to form H bonds with the
molecules along with other dipole interactions
...
A non-polar solute will move much quicker
...
Thin layer chromatography is commonly used to monitor the progress of reactions because it
works quickly
...
Nucleic Acids 2
...
Monomer - molecule that, when repeated, makes up a polymer
...
Polynucleotide - large molecule containing many nucleotides
...
They are phosphate
esters of pentose sugars, where a nitrogenous base is linked
to carbon 1 of the sugar residue, and a phosphate group is
linked to either carbon 5 or 3 of the sugar residue, by
covalent bonds formed by condensation reactions
...
In RNA, the nucleotide pentose sugar is
ribose, and in DNA it is deoxyribose
...
g
...
help regulate metabolic pathways e
...
by ATP, ADP and AMP
...
DNA is found in the nuclei of eukaryotic cells, within the cytoplasm of prokaryotic cells and
inside some viruses
...
DNA is one of the important
macromolecules that make up the structure of living organisms
...
It
may be a purine (adenine or guanine - two
rings) or a pyrimidine (thymine or cytosine
- one ring)
...
Adenine always pairs with thymine, guanine always pairs with cytosine
...
3 H bonds form between G and C
...
These can then twist into the double helix, giving the molecule stability
...
The upright part of the large DNA molecule that resembles a ladder is formed by the sugarphosphate backbones of the antiparallel polynucleotide strands
...
The 5' end of the molecule is where the phosphate group is attached to the fifth carbon atom
of the deoxyribose sugar
...
The rungs of the ladder consist of the complementary base pairs, joined by H bonds
...
In eukaryotic cells, the DNA is organised:
the majority of the DNA content is in the nucleus
each large molecule of DNA is tightly wound around special histone proteins into
chromosomes; each chromosome is therefore one molecule of DNA
there is a loop of DNA without the histone proteins inside mitochondria and
chloroplasts
In prokaryotic cells:
DNA is in a loop within the cytoplasm
it is not wound around histone proteins and is described as naked
Scientists Watson, Crick, Wilkins and Franklin all helped to work out the structure of DNA
...
This DNA can be further purified by removal of
unwanted salts and can be concentrated
...
Helicase - enzyme that catalyses the breaking of H bonds between bases
...
One old strand is converted
in each new molecule
...
Each molecule of DNA replicates
...
In eukaryotes, this results in each chromosome having an identical
copy of itself
...
The
DNA within mitochondria and chloroplasts also replicates each time these organelles divides
(just before the cell divides)
...
It unzips - the H bonds between bases are broken (catalysed by helicase), resulting in
two single strands of DNA with exposed nucleotide bases
...
DNA polymerase catalyses the addition of the new nucleotide bases (5' to 3') to the
single strands of DNA
...
The leading strand is synthesised continuously, while the lagging strand is in
fragments that are later joined, catalysed by ligase
...
The product is two identical DNA molecules
...
The loops of DNA in prokaryotes also replicate semi-conservatively
...
In the 1950s scientists knew DNA was self-replicating and had theories how:
conservative - the original molecule acts as a template and a new molecule is made
dispersive - the original molecule breaks up into nucleotides, each one joins to a
complementary nucleotide and new ones join up again
semi-conservative - the new molecule consists of one original strand and one newly
formed strand
Meselson and Stahl 1958:
Grew bacteria (E
...
This contains an extra neutron in every nucleus
...
Transferred some bacteria into a medium containing the normal 14N nitrogen and left
them to undergo one division
...
This showed DNA does not
replicate conservatively, as that would have produced two bands of DNA, one heavy
and one light
...
This produced two bands of DNA, one hybrid and one light, showing that
replication is semi-conservative and not dispersive
...
This could change the genetic code and cause
mutations
...
However many genes have changes in their nucleotide
sequence
...
Some mutations can be beneficial
...
Polypeptide - polymer made of many amino acid units joined together by peptide
bonds
...
Transcription - process of making messenger RNA from a DNA template
...
RNA is different to DNA:
sugar molecule in each nucleotide is ribose
the nitrogenous base uracil (pyrimidine) replaces thymine
the polynucleotide chain is usually single-stranded and shorter
there are three forms: messenger, transfer and ribosomal
On each chromosome, there are specific lengths of DNA called genes
...
Some proteins are structural e
...
cytoskeleton threads; others make up the cells' 'tool kit' e
...
enzymes
...
As long as this is correct, it will fold correctly
and be held in its tertiary structure, enabling it to carry out its function
...
Genes are inside the nucleus but proteins are made in the cytoplasm
...
In this form, the sequence of base triplets (codons) can
pass out of the nucleus to the ribosome, ensuring the coded instructions are translated and the
protein is assembled correctly
...
It is degenerate because for all amino acids, there is more than one base triplet
...
It is also non-overlapping and read starting from a fixed point in groups of three
bases
...
Transcription:
A gene unwinds and unzips
...
RNA polymerase catalyses the formation of temporary H bonds between RNA
nucleotides and their complementary unpaired DNA bases
...
A length of RNA complementary to the template strand of the gene is produced
...
The mRNA passes out of the nucleus through the nuclear envelope and attaches to a
ribosome
...
These pass separately
out of the nucleus through pores in the
envelope, and then come together to form
the ribosome
...
Translation:
Transfer RNA molecules are made
in the nucleolus and pass out into
the cytoplasm
...
At one end is a trio of nucleotide
bases that recognises and attaches to
a specific amino acid
...
Ribosomes catalyse the synthesis of polypeptides:
tRNA molecules bring amino acids and find their place when the anticodon binds to
the complementary codon on the mRNA molecule
as the ribosome moves along the mRNA, it reads the code and when two amino acids
are adjacent to each other a peptide bond forms between them
ATP is needed for polypeptide synthesis
the amino acid sequence for the polypeptide is determined by the sequence of triplets
of nucleotide bases on the length of DNA (gene)
after the polypeptide has been assembled, the mRNA breaks done and its component
molecules can be recycled into new lengths of mRNA with different codon sequences
the newly synthesised polypeptide is helped by chaperone proteins in the cell, to fold
correctly into its 3D shape or tertiary structure, in order to carry out its function
Enzymes 2
...
Catalyst - chemical that speeds up the rate of reaction and remains unchanged
...
Intracellular - inside the cell
...
Product - molecule produced from substrate molecules by an enzyme catalysed
reaction
...
Enzymes are biological catalysts because they speed up metabolic reactions in living
organisms
...
They speed up chemical reactions and remain unchanged
...
The number of
reactions an enzyme can catalyse per second is called the turnover number
...
They do not require high
temperatures like chemical catalysts
...
They do not produce by-products, and rarely make mistakes
...
The structure of enzymes enables them to carry out their functions:
For enzymes to catalyse some reactions they may need help from cofactors
...
If the gene has a mutation
this may alter the enzyme's structure and prevent it functioning
...
Enzymes catalyse the formation of the organism's structural components (such as
collagen in bones and connective tissue)
...
This
consists of 6-10 amino acids
...
Each type of enzyme is highly specific in its
function
...
Intracellular enzymes:
In any cell there may be up to 1000 metabolic reactions going on at the same time, each
catalysed by a different enzyme
...
consists of four polypeptide chains and contains a haem group with iron
fastest-acting enzyme, with highest turnover number (6 million/second)
in eukaryotic cells, found inside vesicles called peroxisomes
when white blood cells ingest pathogens they use catalase to help kill the invading
microbe
optimum pH in humans is around 7 but varies by species
optimum temp
...
In the digestive system, many enzymes are secreted from cells lining the
alimentary canal into the gut lumen
...
in food
...
Amylase is produced in the salivary glands and acts in the mouth to digest the
polysaccharide starch to the disaccharide maltose
...
Trypsin is made in the pancreas and acts in the small intestine to digest proteins to
smaller peptides by hydrolysing peptide bonds
...
Some (prosthetic groups) are part of the enzyme
structure and others (mineral ion cofactors and organic coenzymes) form temporary
associations with the enzyme
...
Some enzymes only work if another small non-protein molecule is attached to them
...
A cofactor that is permanently bound by covalent bonds to an enzyme
molecule is called a prosthetic group
...
This enzyme is
found in erythrocytes and catalyses the interconversion of carbon dioxide and water to
carbonic acid which then breaks down to protons and hydrogencarbonate ions
...
CO2 + H2O <---> H2CO3 <---> H+ + HCO3This reaction is important as it enables carbon dioxide to be carried in the blood from tissues
to the lungs
...
These ions are also cofactors
...
The presence of certain ions that may
temporarily bind to either the substrate or the enzyme may ease the formation of such ES
complexes and therefore increase the rate of reaction
...
Some cofactors change the charge distribution on the surface of the substrate
molecule or active site and make the temporary bonds easier to form
...
g
...
Coenzymes are a type of cofactor
...
They
bind temporarily to the active site
...
Some stay bound to the enzyme permanently
forming prosthetic groups
...
Some non-metallic ions are cofactors
...
The coenzymes are chemically changed during the reaction and need to
be recycled to their original state (by a different enzyme)
...
If these vitamins are deficient in a
human's diet, certain disease may result
...
A substrate fits into an active site because the tertiary structure is complementary to that of
the active site
...
Temporary H bonds hold the
two together forming an ES complex
...
OR substrate molecules fit into the active site forming an ES complex, bonds form
between the substrate molecules forming an EP complex
...
The substrates and enzymes each have kinetic energy and are constantly moving
randomly
...
The substrate is either broken down or built up into the product molecule and these
form an EP complex whilst still in the active site
...
The enzyme is now able to form another ES complex
...
However, the lock and key hypothesis does not explain how the ES complex is stabilised
...
He suggested:
When the substrate fits into the active site, the active site changes shape slightly to
mould itself around the substrate
...
This moulding enables the substrate to bind more effectively to the active site
...
When the substrates have been converted to the products and are still in the active
site, they form an EP complex
...
The enzyme is now free to catalyse another reaction with another substrate of the
same type
...
Many are heated to provide this energy, as
this increases the kinetic energy so they move about more and are more likely to collide
...
Because enzymes have an active site specific to only the substrate molecules, they
bring the substrate molecules close enough together to react without the need for heat
...
Q10 - temp
...
If a substance is heated:
extra energy in the form of heat causes molecules to move faster
this increases the rate of collisions between molecules
it also increases the force with which they collide
If a reactant mixture containing enzyme and substrate molecules is heated:
both types of molecules will gain kinetic energy and move faster
this will increase the rate of successful collisions
the rate of formation of ES complexes increases, and the rate of reaction increases,
increasing the number of EP complexes per second up to a point
at the optimum temperature, the rate of reaction is at its maximum
As well as making molecules move faster, increasing the temperature also makes them
vibrate:
this may break some of the weak bonds (H and ionic) that hold the tertiary structure of
the active site
as the active site shape changes, the substrates will not fit into it so well so the rate of
reaction will decrease
as more heat is applied, the shape of the active site irreversibly changes so it is no
longer complementary to the shape of the substrate molecule
the reaction cannot proceed, and the enzyme is denatured
Heat does not break peptide bonds between amino acids so the primary structure is not
affected
...
E
...
psychrophilic bacteria have enzymes that can work at very low temperatures
...
Their enzymes are heat stable
...
Rate of reaction (s-1) = 1 / time taken
Q10 refers to the increase in rate of a process when the temp
...
Q10 = rate of reaction at (T + 10C) / rate of reaction at TC
For chemical reactions Q10 is approx
...
For
metabolic reactions between 10 and 40C the rate is also roughly doubled because the
increase in temperature provides more kinetic energy so enzyme and substrate molecules
move faster and collide more often
...
You can use phosphatase to investigate the effect of temperature change
...
Acids such as HCl and H2SO4 dissociate into protons and a negatively charged ion:
HCl H+ + Cl H2SO4 H+ + HSO4Organic acids are also proton donors:
lactic acid dissociates into H+ and lactate
pyruvic acid dissociates into H+ and pyruvate
A buffer is something that resists changes in pH
...
4
...
Some proteins e
...
haemoglobin can also donate or accept protons, so also act as buffers
...
A hydrogen ion has a positive charge so is attracted towards negatively charged
ions/molecules
...
Excess hydrogen ions will interfere with these H bonds and ionic forces so the active
site of the enzyme will change shape
...
Increasing the concentration of hydrogen ions will also alter the charges on the active
site, as more protons will cluster around negatively charged groups in the active site
(e
...
R groups)
...
Enzymes work within a narrow range of pH:
Small pH changes either side of the optimum slow the rate of reaction because the
shape of the active site is disrupted
...
At extreme pH, the enzyme’s active site is denatured (cannot return)
...
Enzymes that work extracellularly may have different optimums e
...
during digestion,
enzymes in the mouth work best at pH 6
...
The acid kills bacteria and other pathogens in
the food
...
8
...
Concentration - number of molecules per unit volume
...
As substrate is added and its concentration increased, the rate of
reaction increases:
more ES complexes can form
more product can form
substrate concentration is the limiting factor because as it increases, the rate of
reaction increases
as the concentration increases further, the reaction reaches its max
...
As ammonia is released, the pH is increased
...
Colorimetry can be used to
measure the depth of colour and therefore the amount of ammonia produced in a set time
...
Control variables:
concentration of enzymes
volume of enzyme and substrate solutions
temperature
time for reaction
stirring/shaking
filter in colorimeter
Depending on a cell’s needs, genes for synthesising particular enzymes can be switched on or
off
...
Advantages:
the elimination of abnormally shaped proteins that might accumulate and harm the
cell
regulation of metabolism in the cell by eliminating any enzymes surplus to
requirements
As enzyme concentration increases:
more active site become available
more successful collisions between enzyme and substrate occur
more ES complexes can form per unit time
enzyme conc
...
The reaction is at its maximum for the fixed substrate conc
...
is increased further, there will be no increase in rate
the enzyme conc
...
is now the limiting factor
In any reaction, the initial rate between the reactants is fastest
...
As the reaction proceeds, substrate molecules are used up as they are converted to
product molecules so the substrate concentration drops
...
The initial rate gives the maximum rate for an enzyme under an experimental situation
...
Inhibitor - substance that reduces or stops a reaction
...
Non-competitive inhibition - inhibition of an enzyme where the competitor attaches to
part of the enzyme but not the active site
...
Inhibitors reduce the activity of an enzyme by combining with the enzyme in a way that
influences how the substrate binds to it, or affects the enzyme’s turnover number
...
Both actions inhibit the formation
of ES complexes
...
More inhibitor molecules means more
can collide with active sites and so the
effect of inhibition is greater
...
If there is enough substrate, the inhibitor is unlikely to collide with the
enzyme
...
Once on the active site, the inhibitor is not affected/changed
...
It reduces the number of free active sites available to bind with substrates
...
If the inhibitor binds irreversibly with the enzyme it is called an inactivator
...
These inhibitors do not compete with the substrates; they attach to the
enzyme at the allosteric site, away from the active site, and disrupt the tertiary structure and
to change its shape
...
The max
...
Adding
more substrate might allow the reaction to
attain this new lower maximum but even very
high substrate concentrations will not allow the
rate of reaction to return to its uninhibited
maximum
...
Some bind reversibly and some irreversibly
...
After the catalysed reaction is complete, product molecules may stay tightly bound to the
enzyme
...
This is
an example of negative feedback
...
Before they can
carry out their function, some amino acids must be removed so their active sites assume the
correct shape or are exposed
...
Many metabolic reactions such as photosynthesis and respiration, involve a series of enzymecatalysed reactions (metabolic pathway):
The product of one reaction becomes the substrate for the next reaction
...
This binding prevents the pathway from running, a type of reversible non-competitive
inhibition
...
Multi-enzyme complexes increase the efficiency of metabolic reactions without increasing
substrate concentration as they keep the enzyme and substrate in the same vicinity and reduce
diffusion time
...
Some enzymes are bound to the organelle membranes
...
Potassium cyanide (KCN) is toxic because it inhibits aerobic respiration and inhibits catalase:
When ingested, KCN is hydrolysed to produce hydrogen cyanide, a very toxic gas
that can dissociate into H+ and CN- ions
...
The venom of the green mamba snake contains a chemical that inhibits the enzyme AChE
...
This causes paralysis, and if the breathing muscles are paralysed the victims die from
suffocation
...
Prostaglandins make nerve cells more sensitive to pain and increase swelling
during inflammation
...
Extracts from foxglove leaves are used to treat heart failure and atrial arrhythmia
...
They inhibit the sodium potassium
pump in the cell membranes of heart muscle cells, and allow more calcium ions to enter the
cells
...
ACE inhibitors are medical drugs that inhibit the angiotensin converting enzyme (ACE)
which normally operates in a metabolic pathway that increases blood pressure
...
They prevent replication of the virus particles within the host cells, by inhibiting protease
enzymes by competitive inhibition
...
They inhibit enzymes involved in
making DNA using the viral RNA as a template
...
g
...
Biological Membranes 2
...
Glycolipid - lipid/phospholipid with a chain of carbohydrate molecules attached
...
Plasma membrane - cell surface membrane
...
Some very small molecules diffuse through the cell membrane in between its
structural molecules
...
Other substances pass through special protein channels or are carried by carrier
proteins
...
The properties of the component molecules of the membrane determine its
permeability
...
These give a large surface
area for some reactions of aerobic respiration and localise some enzymes needed for
respiration to occur
...
Some photosynthesis reactions occur on these membranes
...
The fluid mosaic model explains how cell membranes can be dynamic and interact with the
cells’ environment
...
The lipid molecules can
change places with each other and some proteins may move, giving fluidity
...
Their hydrophilic heads are in contact with the watery exterior/interior
...
There are proteins spanning the membrane:
some have pores and act as channels to allow ions (with electrical charge and
surrounded by water molecules) to pass through
some are carriers and by changing their shape, carry specific molecules across the
membrane
some may be attached to the carrier proteins and function as enzymes, antigens or
receptor sites for complementary shaped signalling chemicals such as hormones
Eukaryotic cell membranes contain cholesterol, which helps regulate the fluidity of the
membrane, maintain mechanical stability and resist the effects of temperature changes on the
structure of the membrane
...
Outside the membrane is the
glycocalyx, formed from the carbohydrate chains attached to either lipids (glycolipids) or
proteins (glycoproteins) in the membrane
...
Neurones have a myelin sheath formed by flattened cells wrapped around them
several times giving several layers of cell membrane
...
Root hair cells have many carrier proteins to actively transport nitrate ions from the
soil into the cells
...
Diffusion - movement of molecules from an area of high concentration to an area of
lower concentration; may or may not be across a membrane; does not involve ATP
...
Cells need to receive raw materials or reactants for the reactions that take place in the cells
...
They also need to remove toxic waste such as carbon dioxide, and
they need to export molecules such as enzymes and hormones
...
Molecules have kinetic energy so will passively diffuse and spread out
...
They have reached equilibrium
...
Fat-soluble molecules such as steroids, can also diffuse through as they
can dissolve in the lipid bilayer, even though they are larger
...
However, water is present in such great
concentrations that significant direct diffusion does happen
...
Many molecules entering cells then pass into organelles and are used for metabolic reactions
...
For
example oxygen diffusing into the cytoplasm of a respiring cell, into the mitochondria and
then used for aerobic respiration
...
This means they diffuse through
water-filled protein channels (pores) embedded in the membrane
...
8nm in
diameter
...
Glucose molecules are too
large to diffuse through the protein channels
but can bind to a transmembrane carrier
protein which opens to allow the glucose to
pass through
...
Different cells have membranes with
differing proportions of transmembrane protein channels and carriers
...
Neurone plasma membranes have many channels specific to either sodium ions or
potassium ions
...
At synapses, there are also calcium ion channels
and there may be chloride ion channels
...
Osmosis - passage of water molecules down their water potential gradient, across a
partially permeable membrane
...
In a solution, the liquid in which the solute is dissolved in is called the solvent
...
The net diffusion from a region of higher water concentration
to a region of lower water concentration, down a concentration gradient, across a partially
permeable membrane, is called osmosis
...
If the solute molecules
dissociate into ions such as
sodium and chloride ions, they
exert more effect on the relative
number of water molecules than
do larger non-polar molecules
...
Water potential is a measure of the tendency of water molecules to diffuse from one region to
another
...
Endocytosis - bulk transport of molecules too large to pass through a cell membrane,
into a cell
...
Sometimes cells need to move substances against their concentration gradient
...
Cells or organelles may also need to accumulate
more of a particular ion than they could do by simple/facilitated diffusion alone
...
They also have a region that binds to and allows hydrolysis of a molecule of ATP to
release energy
...
For example, in guard cells ATP made by chloroplasts provides energy to actively transport
potassium ions from surrounding cells into the guard cells
...
As the guard cells swell, their tips bulge
and this opens the stoma
...
They do this by bulk transport, which requires energy from ATP
...
Exocytosis:
how large molecules are exported out of cells
a vesicle containing the molecules is moved towards the cell and fuses with the
plasma membrane
the plasma membrane and the membrane of the vesicle fuse
the fused site opens, releasing the contents of the vesicle
ATP is needed to fuse the membranes together as well as for moving the vesicles
When temperature drops:
Saturated fatty acids become compressed
...
This maintains membrane fluidity
...
Cholesterol in the membrane also buffers the effect of lowered temperature to prevent
reduction in the membrane’s fluidity
...
Some organisms such as fish and plants an change the composition of the fatty acids
in their cell membranes in response to lowered temperatures
...
Permeability increases
...
If
some enzymes drift sideways this could alter the rate of reaction
...
Presence of cholesterol buffers the effects of increasing heat as it reduces the increase
in membrane fluidity
...
However proteins are not as stable:
high temperatures cause the atoms within their large molecules to vibrate and this
breaks the H and ionic bonds holding their structure together
tertiary structure changes and cannot change back – they are denatured
Just underneath the plasma membrane are cytoskeleton threads made of protein
...
It will become more permeable as holes appear in it
...
To investigate the effect of temperature on beetroot cell membranes:
Inside beetroot cells, within the vacuole, are nitrogenous water-soluble pigments
called betacyanins
...
The amount of leakage is proportional to the degree of damage to the beetroot plasma
and tonoplast membrane and can be measured with a colorimeter
...
In some plants, the plasma membrane acts as a heat sensor
...
These
bind to misshapen proteins, preventing further damage
...
6
Cytokinesis - cytoplasmic division following nuclear division, resulting in two new
daughter cells
...
Mitosis - type of nuclear division that produces daughter cells genetically identical to
each other and to the parent cell
...
Cells reproduce by duplicating their contents and then splitting into two daughter cells
...
Nuclear and cytoplasmic division (the M phase) occupy
only a small part of the cell cycle
...
During interphase, there are elaborate
preparations being made for cell division in a carefully
ordered and controlled sequence with checkpoints
...
There are other
checkpoints e
...
during mitosis
...
The number is about 50 and is called the
Hayflick limit
...
The prokaryotic cell cycle occurs by a process called binary fission
...
Before the cell divides, its DNA is replicated
...
Each cell contains replicated plasmids and synthesised ribosomes
...
Phase of cell cycle + checkpoints
M phase
a checkpoint chemical triggers
condensation of chromatin
halfway through the cycle, the
metaphase checkpoint ensures the cell
is ready to complete mitosis
G0 (gap 0) phase
a resting phase triggered during early
G1 at the restriction point by a
checkpoint chemical
Events within the cell
cell growth stops
mitosis, consisting of prophase, metaphase,
anaphase, telophase
cytokinesis (cytoplasmic division)
cells may undergo apoptosis (programmed
cell death), differentiation or senescence
some cells remain in this phase indefinitely
some cells do not have this phase
G1 (gap 1) phase / growth phase
at G1 checkpoint control mechanism
ensures the cell is ready to enter the S
phase and begin DNA synthesis
S (synthesis) phase of interphase
because chromosomes are unwound
and DNA is diffuse, every DNA
molecule is replicated; there is a
specific sequence to the replication of
genes
G2 (gap 2) phase of interphase
special chemicals ensure the cell is
ready for mitosis by stimulating
proteins that will be involved
cells grow and increase in size
transcription of genes to make RNA
organelles duplicate
biosynthesis including making the enzymes
needed for DNA replication in the S phase
p53 (tumour suppressor) gene helps control
this phase
once the cell has entered this phase it is
committed to completing the cell cycle
DNA replicates
when all chromosomes are duplicated, each
one consists of a pair of identical sister
chromatids
this phase is rapid and because the exposed
DNA base pairs are more susceptible to
mutagenic agents, this reduces the changes
of spontaneous mutations
cells grow
Chromatids - replicates of chromosomes
...
All living organisms need to produce genetically identical daughter cells by mitosis for the
following reasons:
Asexual reproduction: single-celled protoctists divide by mitosis to produce new
individuals
...
Fungi can
reproduce asexually by mitosis
...
Aphids may sometimes produce eggs by mitosis
that do not require fertilisation
...
Tissue repair: wounds heal when growth factors (secreted by platelets and
macrophages and damaged cells of the blood vessel walls) stimulate the proliferation
of endothelial and smooth muscle cells to repair damaged blood vessels
...
In plants, cells in the meristem and cambium can divide by mitosis
...
Haploid - having only one set of chromosomes represented by 'n'
...
May contain different alleles
...
Sexual reproduction increases genetic variation because it involves combining genetic
material from two individuals by the process of fertilisation
...
In many organisms, body cells are diploid
...
The diploid cells undergoing meiosis are in specialised organs
called gonads (ovaries and testes)
...
There are 46 chromosomes in human body cells (23 from the mother and 23 from the father)
...
Although they have the
same gene, they may contain different alleles for the gene (versions of the gene)
...
In meiosis
the chromosomes pair up in their homologous pairs:
there are two divisions in meiosis and each one has four stages
the cell may enter a short interphase between the divisions
the second division occurs in a plane at right angles to that of the first division
at the end of the second division, cytokinesis may occur
Stage of Meiosis (FIRST DIVISION)
Events during this stage
the chromatin condenses and each
chromosome supercoils
...
Epithelial cells - cells that make up lining tissue
...
Neutrophil - type of white blood cell that is phagocytic (can ingest microbes and small
particles)
...
Within a single-celled organism, the division of labour is determined by the organelles each
of which has a specific function
...
Multicellular organisms are larger and therefore have a smaller
SA:V ratio, which means most of their cells are not in direct contact with the external
environment
...
Multicellular eukaryotic organisms start life as a single undifferentiated cell called a zygote
...
The zygote is not specialised and all the genes in its
genome are able to be expressed
...
It is a stem cell
...
These embryonic cells differentiate as certain genes are switched off and other genes may be
expressed more, so:
the proportions of the different organelles differ from those of other cells
the shape of the cell changes
some of the contents of the cell change
Therefore, each cell type is specialised for a particular function
...
Erythrocytes are adapted in several ways:
very small (7
...
g
...
Palisade cells - closely-packed photosynthetic cells within leaves
...
Palisade cells are well adapted for photosynthesis because:
they are long and cylindrical so they pack together closely with little space between
them for air to circulate; carbon dioxide in these air spaces diffuses into the cells
they have a large vacuole so the chloroplasts are positioned nearer to the periphery of
the cell, reducing carbon dioxide’s diffusion distance
they contain many chloroplasts
they contain cytoskeleton threads and motor
proteins to move the chloroplasts, nearer to
the upper surface of the leaf where sunlight
intensity is low and further down when it is
high
Guard cells are within the lower epidermis and
contain chloroplasts, however they cannot carry out
photosynthesis as they don’t have the right enzymes
...
the hair-like projection greatly increases the surface area for absorption of water and
mineral ions such as nitrates, from the soil
mineral ions are actively transported into the root hair cells, lowering the water
potential within them and causing water to follow by osmosis down the water
potential gradient
the root hair cells have special carrier proteins in the plasma membranes to actively
transport the mineral ions in
these cells will also produce ATP as this is needed for active transport
Tissue - group of cells that work together to perform a specific function
...
g
...
It
has the following characteristics:
made up entirely of cells
cells are very close together and form continuous sheets
adjacent cells are bound together by lateral contacts
no blood vessels within the tissue; cells receive nutrients by diffusion from tissue
fluid in the underlying connective tissue
some epithelial cells have smooth surfaces but some have cilia or microvilli
epithelial cells have short cell cycles and divide 2/3x per day to replace damaged
tissue
epithelial tissue is specialised to carry out its functions of protection, absorption,
filtration, excretion and secretion
Connective tissue consists of a non-living extracellular matrix containing proteins (collagen
and elastin) and polysaccharides
...
Examples include blood, bone, cartilage,
tendons, skin
...
Muscle cells are called fibres and are elongated,
containing special organelles called myofilaments made of the proteins actin and myosin
...
There are 3 types of muscle tissue:
skeletal muscles – when contracted, cause bones to move
cardiac muscle – makes up walls of the heart and allows it to beat and pump blood
smooth muscle – occurs in walls of intestine and blood vessels, propels substaces
along these tracts
Meristem - area of unspecialised cells within a plant that can divide and differentiate
into other cell types
...
Phloem - tissue that carries products of photosynthesis in plants
...
Plants contain tissues made of specialised cells
...
Some cells have walls impregnated with a
waxy substance forming a cuticle
...
Vascular tissue is xylem and phloem:
o xylem carries water and minerals from roots to all parts of the plant
o phloem sieve tubes transfer photosynthesis products in solution from leaves to
other parts of the plant such as flowers and shoots
Meristematic tissue contains stem cells
...
It is found in roots and shoot tips and in the cambium of vascular bundles
...
However new cells can arise at the meristems by mitosis
...
sieve tubes lose most organelles and sieve plats develop between them
companion cells retain their organelles and continue metabolic functions to provide
ATP for active loading of sugars into the sieve tubes
Parenchyma is packing tissue and fills spaces between other tissues
...
In aquatic plants,
aerenchyma tissue is parenchyma with air spaces to keep the plant buoyant
...
Sclerenchyma cells have lignified walls and these cells strengthen stems and leaves
...
System
Digestive system
Circulatory
system
Respiratory
system
Urinary system
Organs and tissues involved
Oesophagus, stomach,
intestines, liver, pancreas
Heart, blood vessels
Examples
Nutrition to provide ATP and
materials for growth and repair
Transport to and from cells
Airways, lungs, diaphragm,
intercostal muscles
Kidneys, ureters, bladder
Breathing and gaseous exchange
excretion
Excretion and osmoregulation
Integumentary
system
Musculo-skeletal
system
Immune system
Nervous system
Skin, hair, nails
Skeleton, skeletal muscles
Bone marrow, thymus gland,
skin, stomach acid, blood
Brain, spinal cord, nerves
Endocrine system Glands that make hormones
Reproductive
system
Lymph system
Testes, penis, ovaries, uterus,
vagina
Lymph nodes and vessels
Waterproofing, protection,
temperature regulation
Support, protection, movement
Protection against pathogens
Communication, control,
coordination
Communication, control,
coordination
Reproduction
Transports fluid back to the
circulatory system and important in
resisting infections
Stem cell - unspecialised cell able to express all its genes and divide by mitosis
...
amongst
differentiated cells; they act like a repair system because they are a renewing source
of undifferentiated stem cells
induced pluripotent stem cells – developed in labs by reprogramming differentiated
cells to switch on certain genes to become undifferentiated
Potential uses:
Bone marrow transplants:
o to treat blood diseases and immune diseases
o to restore patient’s blood system after cancer treatments where the patient’s
bone marrow cells can be obtained before treatment, stored and then put back
into the patient after treatment
Drug research:
o if stem cells can be made into different types of human tissue then drugs can
be tested on these tissues before animal tissues
Developmental biology:
o scientists can study how these cells develop to make particular cell types (e
...
blood) and can learn how each cell type functions and see what goes wrong
when they are diseased
o they are trying to find out if they can extend the capacity that embryos have
for growth and tissue repair, into later life
Repair of damaged tissues or replacement of lost tissues:
o stem cells have been used to treat mice with type 1 diabetes, and research is
underway for use in humans
o bone marrow stem cells can be made to develop into liver cells
o stem cells directed to become nerve tissue could be used to treat Alzheimer
and Parkinson diseases or repair spinal cord injuries
o stem cells may be used to populate a bioscaffold of an organ and then directed
to develop and grow into specific organs for transplanting (regenerative
medicine); this could mean there is no need for immunosuppressant drugs
o stem cells may eventually be used to treat conditions such as arthritis, strokes,
burns, vision and hearing loss, and heart disease
Exchange Surfaces and Breathing 3
...
In small organisms, the gas exchange can take place over the surface of the body, and they do
not need a specialised exchange system
...
Three main factors that affect need for an exchange system:
size
surface area to volume ratio
level of activity
In small organisms, all the cytoplasm is close to the environment, and diffusion can supply
enough oxygen and nutrients to keep the cells alive and active
...
Diffusion is too slow to
enable sufficient supple to the innermost cells
...
The surface area is
relatively larger compared to the volume (large SA:V ratio)
...
Large organisms have a larger surface area but also a larger volume
...
Some organisms increase their SA:V ratio e
...
flatworms have a thin flat body
...
Most large organisms need a
range of tissues to give the body support and strength
...
The cells of an active organism need a good supply of oxygen to supply energy
for movement
...
Features of a good exchange system:
large surface area to provide more space for molecules to pass through, often achieved
by folding walls/membranes involved (e
...
root hairs)
thin permeable barrier to reduce diffusion distance (e
...
alveoli in lungs)
good blood supply that can bring fresh supplies of molecules to the supply side,
keeping the concentration high or remove molecules from the demand side to keep the
concentration low (important to maintain steep concentration gradient)
Alveoli - tiny folds of the lung epithelium to increase the surface area
...
Diaphragm - a layer of muscle beneath the lungs
...
Contraction of the external intercostal
muscles raises the ribcage
...
Ventilation - the refreshing of the air from the lungs so there is a higher oxygen
concentration than in the blood, and a lower carbon dioxide concentration
...
Air can pass into the
lungs though the nose, along the trachea, bronchi and bronchioles and finally into tiny airfilled sacs called alveoli
...
The ribs are held together by
intercostal muscles
...
Gases pass by diffusion through the walls of the alveoli
...
The lungs must maintain a steep concentration gradient in each direction to
ensure diffusion can occur
...
o Alveoli are lined with moisture which evaporates as you breathe out
...
Barrier to exchange is permeable to oxygen and carbon dioxide:
o The barrier is the wall of the alveolus and of the blood capillary
...
Thin barrier to reduce diffusion distance:
o The alveolus wall and capillary wall are both one cell thick
...
o The capillaries are in close contact with the alveolus walls
...
o Total barrier to diffusion is less than 1 micro metre thick
...
o The blood system transports carbon dioxide from the tissues to the lungs,
ensuring the concentration of carbon dioxide in the blood is higher than that in
the air of the alveoli
...
o The blood transports oxygen away from the lungs ensuring the concentration
of oxygen in the blood is lower than that in the alveoli so oxygen diffuses into
the blood
...
Therefore, the concentration gradient necessary for diffusion is maintained
...
The external intercostal muscles contract to raise
the ribs
...
The pressure in the chest cavity drops
below the atmospheric pressure, and air is moved into the lungs
...
The external
intercostal muscles relax and the ribs fall
...
The volume of the
chest cavity is decreased
...
Cartilage - a form of connective tissue
...
Elastic fibres - protein fibres that can deform and then recoil to their original size
...
Smooth muscle - involuntary muscle that contracts without the need for conscious
thought
...
The airways (trachea, bronchi and bronchioles) must meet certain requirements:
large enough to allow sufficient air to flow without obstruction
supported to prevent collapse when air pressure inside is low during inspiration
flexible to allow movement
The airways are lined with ciliated epithelium which contribute to keeping the lungs healthy
...
The cilia move the
mucus up to the top of the airway
Tissues in the
where it is swallowed
...
The trachea and bronchus walls have
a similar structure; however, bronchi
are narrower than the trachea
...
The rings of
cartilage in the trachea are C-shaped
to allow flexibility and space for food
to pass down the oesophagus
...
The larger ones may have cartilage but
smaller ones don't
...
The smallest
bronchioles end in clusters of alveoli
...
This restricts the flow of
air to and from the alveoli
...
The contraction of muscle is not voluntary and may happen because of
an allergic reaction
...
The elastic fibres are deformed and recoil to
their original size and shape, dilating the airway
...
Draw a tissue plan
(contains no individual cells)
...
g
...
)
Breathing rate - number of breaths per minute
...
Tidal volume - volume of air inhaled or exhaled in one breath usually measured at
rest
...
Vital capacity - the greatest volume of air that can be expelled from the lungs after
taking the deepest possible breath
...
A float-chamber
spirometer consists of a chamber of air
floating on a tank of water
...
During
expiration, the air returns to the chamber,
raising the lid
...
The carbon dioxide rich air exhaled
is passed through a chamber of soda lime which absorbs the carbon dioxide
...
Precautions that must be taken when using a spirometer:
healthy subject free from asthma
soda lime fresh and functioning
no air leaks in the apparatus
mouthpiece sterilised
water chamber not overfilled
Lung volumes:
The total lung volume consists of the
vital capacity and the residual
volume
...
It is usually
between 2
...
This depends on
factors such as:
o size of the person
o age and gender
o level of regular exercise
The residual volume is the volume of
air that remains in the lungs after
forced expiration
...
1
...
Tidal volume is the volume of air moved in and out with each breath at rest
...
5dm3
...
Breathing supplies oxygen for respiration and removes
carbon dioxide produced in respiration
...
This
carbon dioxide is absorbed by the soda lime, so the
volume of air in the chamber decreases
...
Therefore, measuring the gradient of the decrease in volume
enables us to calculate the rate of oxygen uptake
...
e
...
3 /
55 = 0
...
Buccal cavity - the mouth
...
Filaments - slender branches of tissue that make up the gill
...
Lamellae/gill plates - folds of the filament to increase surface area
...
Spiracle - an external opening or pore that allows air in or out of the tracheae
...
Tracheal system - system of air-filled tubes in insects
...
They use gills to absorb oxygen
dissolved in the water and release carbon dioxide
...
Each gill consists of two rows of gill filaments (primary lamellae) attached to a bony arch
...
This provides a large surface area
...
To dissect a fish gill:
1
...
2
...
Note the gill slits or spaces between the
gills
...
Cut out one gill
...
4
...
Blood flows along the gill arch and out along the filaments to the secondary lamellae
...
This creates a countercurrent flow that absorbs the maximum amount of oxygen
from the water by ensuring there is always an oxygen concentration gradient
...
The buccal
cavity can change volume
...
The mouth closes and the floor is raised again pushing water through the gills
...
This movement
reduces the pressure in the opercular cavity (space under operculum) helping water flow
through the gills
...
Insects don't transport oxygen in the blood
...
Circulation is slow and affected by body
movement
...
Air
enters the system via a pore in each segment called
a spiracle
...
These divide into
smaller tubes called tracheoles
...
Gaseous exchange occurs between the air in the
tracheole and the tracheal fluid
...
Many insects are active and need a good supply of
oxygen
...
This means more oxygen can be
absorbed
...
This can be
achieved in several ways:
In many insects, sections of the tracheal system are expanded and have flexible walls;
these act as air sacs, and can be squeezed by action of flight muscles
...
Movement of the wings alter the volume of the thorax
...
When the
thorax volume increases, the pressure drops and air is pushed into the system from
outside
...
These are coordinated with opening and closing valves in the spiracles
...
As it reduces, spiracles at the rear end of the body open and air leaves the
system
...
2
Double circulatory system - one in which blood flows through the heart twice for each
circuit of the body
...
Transport - movement of substances (oxygen, nutrients, hormones, waste, heat etc
...
All living things need a supply of oxygen and nutrients and removal of waste products so
they don't build up and become toxic
...
Diffusion is
enough to keep the cells alive
...
Factors that influence need for a transport system:
size
surface area to volume ratio
level of metabolic activity
In terms of size, the cells inside a large organism are further from its surface (diffusion
pathway is increased)
...
Also, the outer layers of cells use up the supplies so less will reach the cells
further inside the body
...
For each gram of body tissue, they have a sufficient
area of the body surface through which exchange can occur
...
Animals need energy from food to move around
...
If an animal is active, its cells need a good supply of nutrients
and oxygen to supply energy
...
Features of a good transport system:
fluid/medium to carry nutrients, oxygen and wastes around the body - blood
a pump to create pressure to push the fluid around the body - the heart
exchange surfaces that enable substances to enter and leave the blood when needed the capillaries
tubes/vessels to carry the blood by mass flow
two circuits - one to pick up oxygen and another to deliver it to tissues
Fish have a single circulatory system
...
Heart -> gills -> body -> heart
...
This has two separate circuits
...
This is pulmonary circulation
...
This is systematic circulation
...
Heart -> body -> heart -> lungs -> heart
...
The blood can flow quicker by increasing the blood pressure
...
Therefore they need less energy and the single circuit is enough
...
The cells need a good supply of both nutrients and oxygen and removal of waste products
...
Arterioles - small vessels that distribute blood from an artery to the capillaries
...
Closed circulatory system - one in which blood is held in vessels
...
Veins - vessels that carry blood back to the heart
...
An open circulatory system means the blood is not always held in blood vessels
...
In some animals movement of the body circulates the blood and without movement
the blood stops moving
...
Blood from the body enters the
heart through pores called ostia
...
At the forward end of the heart the blood pours out into the body cavity
...
Some larger and more active insects have open-ended tubes attached to the heart
...
Disadvantages of open circulatory systems:
low blood pressure and slow blood flow
circulation of blood may be affected by body movements
Larger animals have a closed circulatory system
...
A
separate fluid (tissue fluid), bathes the tissues and cells
...
All
blood vessels have an inner layer made from a single layer of cells called the endothelium
...
Arteries carry blood away from the heart
...
The lumen is relatively small to maintain high
pressure and the inner wall is folded to allow the lumen to
expand as blood flow increases
...
Middle layer (tunica media) - a thick layer of smooth
muscle
...
This
provides strength to withstand the high pressure and recoil to maintain the pressure
...
Further from the heart, the
walls contain more muscle tissue
...
Arteriole walls contain a layer of
smooth muscle
...
This
increases resistance to flow and reduces the rate of flow of blood
...
Capillaries have very thin walls, and allow exchange of materials
between the blood and tissue fluid
...
The red blood cells are squeezed against the walls of the
capillary as they pass along, helping transfer oxygen as it
reduces the diffusion path to the tissues
...
The walls consist of a single layer of flattened endothelial
cells
...
The walls are leaky, allowing blood plasma and dissolved substances to leave the
blood
...
These collect blood from
the capillary bed and lead into the veins
...
Veins carry blood back to the heart
...
The lumen is large to ease flow of blood
...
Veins contain valves to help the blood flow back to the
heart and prevent backflow
...
Contraction of this muscle applies
pressure to the blood and forces it to move along in the
right direction
...
Hydrostatic pressure - pressure a fluid exerts when pushing against the sides of a
vessel
...
Oncotic/osmotic pressure - pressure created by the osmotic effects of the solutes
...
Tissue fluid - the fluid surrounding the cells and tissues
...
The plasma contains
oxygen, carbon dioxide, minerals, glucose, amino acids, hormones, and plasma proteins
...
Tissue fluid is like plasma, but does not contain most of the cells found in blood, or plasma
proteins
...
It surrounds the cells
in the tissue and supplies them with oxygen and nutrients
...
This movement is mass
flow
...
Formation of tissue fluid:
When an artery reaches the
tissues, it branches into a capillary
network
...
At the arterial end of a capillary,
the blood is at relatively high
hydrostatic pressure
...
The fluid can leave
through gaps between the cells
...
All cells
and plasma proteins remain in the
blood as they are too large to fit
through the gaps in the capillary
walls
...
The exchange occurs by diffusion, facilitated diffusion and
active transport
...
This allows some of the
tissue fluid to return to the capillary carrying waste substances into the blood
...
Some is directed into the lymphatic system
...
The fluid in the lymphatic system is called lymph and is similar to tissue fluid
...
Lymph nodes are
swellings found at intervals along the lymphatic system which play an important role in the
immune response
...
The tissue fluid has its own hydrostatic pressure and the oncotic pressure
of the solutes also has an influence
...
The hydrostatic pressure of the tissue fluid pushes fluid into the capillaries
...
The oncotic pressure of the tissue fluid pulls water into the tissue fluid
...
Atrio-ventricular valves - valves between the atria and ventricles that ensure blood
flows in the right direction
...
Semilunar valves - valves that prevent blood re-entering the heart from the arteries
...
The left
side pumps oxygenated blood to the rest of the body
...
The pressure forces the blood along the arteries and through
the circulatory system
...
There are two
main pumping chambers, the ventricles
...
These are much
smaller than the ventricles
...
If these arteries become constricted, it can have
severe consequences, as there will be reduced delivery of oxygen and nutrients
...
At the top of the heart, there are tubular blood
vessels - veins that carry blood into the atria and the arteries that carry blood away from the
heart
...
Deoxygenated blood from the body flows
through the vena cava into the right atrium
...
From the atria, blood flows down the
atrio-ventricular valves into the ventricles
...
A wall of
muscle called the septum separates the
ventricles from each other
...
Deoxygenated blood leaving the right ventricle flows into the pulmonary artery leading to the
lungs, where it is oxygenated
...
This carries blood to arteries that supply all parts of the body
...
These prevent blood returning to the heart as the
ventricles relax
...
Cut into each ventricle noting the thickness of the walls
...
Cut upwards towards the atria to expose the atrio-ventricular valves
...
The cardiac muscle in the wall of each chamber contracts to create pressure in the blood
...
Their function is just to receive blood from the veins and push
it into the ventricles
...
This
enables the right ventricle to pump blood out of the heart to the lungs
...
Also, the alveoli in the lungs are delicate and
could be damaged by high blood pressure
...
The blood is pumped all around the body and needs sufficient
pressure to overcome the resistance of the systematic circulation
...
These fibres help
spread the stimulus around the heart and ensure the muscle can produce a squeezing action
...
The muscle cells are separated by intercalated discs which facilitate synchronised
contraction
...
Cardiac cycle - the sequence of events in one full heartbeat
...
The walls
of the four chambers must all contract in a coordinated sequence to allow the heart to fill with
blood before pumping it away
...
Contraction starts at the
apex (base) of the heart so blood is pushed upwards towards the arteries
...
Elastic recoil causes them to increase in volume
allowing blood to flow in from the veins
...
The muscle in the walls is thin so
only a small amount of pressure is created
...
The valves prevent backflow, and are opened and closed by changes in the blood pressure in
the heart chambers
...
pressure in ventricles drops below pressure in atria
blood in atria pushes atrio-ventricular valves open
blood entering the heart flows through atria and into ventricles
pressure in atria and ventricles rises as they fill with blood
valves remain open while atria contract but close when atria relax
this closure is caused by swirling action in the blood around the valves when the
ventricle is full
as ventricles contract, the pressure of the blood in ventricles rises
when pressure rises above that in the atria, blood moves upwards
this movement fills the valve pockets and keeps them closed
tendinous cords attached to the valves prevent them from turning inside out
this prevents back flow of blood into the atria
Semilunar valves:
before ventricular contraction, pressure in the major arteries is higher than that in the
ventricles
this means semilunar valves are closed
ventricular systole raises blood pressure in the ventricles quickly
once pressure in the ventricles rises above pressure in the arteries, the semilunar
valves are pushed open
the blood is under high pressure so is forced out of ventricles
once ventricles have finished contracting, the heart muscle starts to relax (diastole)
elastic tissue in the walls of the ventricles recoils
this stretches the muscle out and returns the ventricle to its original size
this causes the pressure in the ventricles to drop rapidly
as it drops below the pressure in the arteries, blood starts to flow back towards the
ventricles
the semilunar valves are pushed closed by the blood collecting in the pockets of the
valves
this prevents blood returning to the ventricles
the 'pulse' is the pressure wave created when the left semilunar valve closes
The pressure changes that cause the opening and closing of the valves (left):
Blood enters the aorta and pulmonary artery in a rapid spurt, but the tissues require blood
delivered in an even flow
...
Ectopic heartbeat - an extra beat or early beat of ventricles
...
Fibrillation - uncoordinated contraction of the atria and ventricles
...
Purkyne tissue - consists of specially adapted muscle fibres that conduct the wave of
excitation from the AVN down the septum to the ventricles
...
Tachycardia - rapid heart rhythm
...
The muscle
contracts and relaxes rhythmically even if not connected to the body
...
The heart needs a mechanism
that can coordinate the contractions of all four chambers for efficient pumping
...
This is a small patch of tissue that
generates electrical activity
...
It's
also known as the pacemaker
...
At the top of the septum is the atrio-ventricular node
(AVN)
...
The wave is delayed in the node, allowing time for the atria to finish contracting and for
blood to flow into the ventricles
...
Some
electrical activity generated by the hear spreads outwards to the skin, so sensors can pick up
the electrical excitation and turn it into a trace
...
g
...
Dissociation - releasing oxygen from the oxyhaemoglobin
...
Haemoglobin - red pigment used to transport oxygen in the blood
...
Haemoglobin + oxygen -> oxyhaemoglobin
...
Each subunit consists of a polypeptide
chain and a haem (non-protein) group
...
The haem group has a high affinity for
oxygen
...
Oxygen is absorbed into the blood as it passes the alveoli in the lungs
...
It binds reversibly, taking the oxygen molecules out of solution and
maintaining a steep concentration gradient allowing more oxygen to enter the blood from the
lungs and diffuse into the cells
...
Oxyhaemoglobin releasing oxygen is called dissociation
...
The concentration of oxygen is measured
by the relative pressure that it contributes to a mixture of gases
...
It is also called the oxygen tension, measured in kPa
...
This is called the
haemoglobin dissociation curve
...
This is because the haem groups that attract the oxygen are
in the centre of the haemoglobin molecules, making it difficult for the oxygen to reach the
haem group and associate with it
...
When one oxygen molecule enters the haemoglobin
molecule it causes a slight change in the shape of the haemoglobin, called a conformational
change
...
As the haemoglobin approaches 100%
saturation, the curve levels off
...
The
oxygen tension found in the lungs is
sufficient to produce close to 100%
saturation
...
Fetal haemoglobin has a higher affinity for oxygen than adult
...
In the placenta where oxygen tension is low, fetal haemoglobin will absorb oxygen from the
surrounding fluid, reducing oxygen tension further
...
This reduces the oxygen tension within the mother's
blood, which makes the maternal haemoglobin dissociate
...
Chloride shift - the movement of chloride ions into the erythrocytes to balance the
charge as hydrogencarbonate ions leave the cell
...
Haemoglobinic acid - the compound formed by the buffering action of haemoglobin
as it combines with excess hydrogen ions
...
It is transported in three ways:
5% is dissolved into the plasma
10% is combined with haemoglobin to form carbaminohaemoglobin
85% is transported in the form of hydrogencarbonate ions (HCO 3-)
Carbon dioxide in the plasma diffuses into red blood cells where it combines with water to
form carbonic acid
...
This carbonic acid dissociates to release H + ions and HCO3- ions:
H2CO3 --> HCO3- + H+
The hydrogencarbonate ions diffuse out of the red blood cell into the plasma
...
The hydrogen ions building up in the red blood cell could cause the red blood cell to become
acidic, and to prevent this they are taken out of solution by associating with haemoglobin to
produce haemoglobinic acid (HHb)
...
Blood entering respiring tissues carries oxygen as oxyhaemoglobin
...
As a result, oxyhaemoglobin dissociates and releases oxygen to the tissues
...
When the tissues are active there is more carbon dioxide released, which
has a dramatic effect on the haemoglobin
...
Carbon dioxide enters the red blood cells forming carbonic acid which dissociates to
release hydrogen ions
...
Changes in pH can affect tertiary structure of the haemoglobin
...
The haemoglobin is unable to hold as much oxygen and oxygen is released from the
oxyhaemoglobin to the tissues
...
Therefore, there will be
more hydrogen ions produced in the red
blood cells
...
When more carbon
dioxide is present, haemoglobin becomes less
saturated with oxygen
...
This Bohr effect results in
more oxygen being released where more
carbon dioxide is produced in respiration
...
Transport in Plants 3
...
Meristem - a layer of dividing cells
...
Vascular tissue - consists of cells specialised for transporting fluids by mass flow
...
Large plants have a small surface area to volume ratio so need specialised exchange surfaces
and a transport system
...
However, demand for water and sugars is high
...
Leaves can perform gaseous exchange and make sugars by photosynthesis
but can't absorb water from the air therefore plants need a transport system to move:
water and minerals from the roots to the leaves
sugars from the leaves to the rest of the plant
The transport system in plants consists of specialised vascular tissue:
water and soluble mineral ions travel upwards in xylem tissue
assimilates (sugars + amino acids) travel up or down in phloem tissue
Xylem and phloem are highly specialised to perform their function
...
Dicotyledonous plants have two seed leaves and characteristic distribution of vascular tissues
...
The vascular bundle is at the centre of a
young root
...
The phloem is found
in between the arms of the X
...
Around the
vascular bundle is a sheath of cells - the
endodermis
...
Inside the endodermis
there is a layer of meristem cells (able to divide) called the pericycle
...
In non-woody plants the
bundles are separate and discrete, in woody plants the bundles are separate in young stems
but become a continuous ring in old stems
...
The xylem is found towards the
inside of the bundle and the phloem
towards the outside
...
In a leaf the vascular bundles form the
midrib and veins
...
Within each vein the xylem is located on top of the phloem
...
This can be demonstrated with
celery stalks however can also be carried out with busy lizzie stems
...
To observe plant tissue:
1
...
Place the section on a slide
3
...
Cover with a coverslip and observe using a light microscope
...
Sieve tube elements - make up the tubes in phloem tissue that carry sap up and down
the plant
...
Xylem vessels - tubes that carry water up the plant
...
Consists of:
vessels to carry the water and mineral ions
fibres to support plant
living parenchyma cells that act as packing tissue to separate and support vessels
As xylem vessels develop, lignin impregnates the walls of the cells making them waterproof
...
The end walls and contents of the cells decay leaving a long column of
dead cells with no content - the xylem vessel
...
This keeps vessels open even when water is in short supply
...
This prevents the vessel from being too rigid and allows
flexibility
...
These form bordered pits
...
They also allow water to leave the xylem and pass into the living parts of the plant
...
The sucrose is dissolved in
water to form sap
...
Elongated sieve tube elements are lined up to form sieve
tubes
...
At the ends of the sieve
tube elements are perforated cross walls called sieve plates
...
The sieve tubes have thin walls
...
They also serve as a mechanism to block the sieve tube
after injury or infection
...
This prevents loss of sap and inhibits
transport of pathogens around the plant
...
They carry out the metabolic processes needed to
load assimilates actively into sieve tubes
...
This allows communication and flow of substances between the cells
...
The cellulose cell walls of a plant cell are fully permeable to water
...
Many plant cells are joined by cytoplasmic bridges
...
There are three pathways water can take through a plant:
Apoplast - water passes through spaces in the cell walls and between
cells
...
Symplast - water enters the cytoplasm through the membrane, passes
through plasmodesmata between cells
...
Water potential is a measure of the tendency of water molecules to move from one place to
another
...
Pure water is 0kPa
...
Therefore, the water potential in plant cells is always negative
...
However, the cell will not absorb water until it bursts, as the cell has a strong cellulose cell
wall
...
As the
pressure potential builds up it reduces the influx of water
...
As the cell loses water the cytoplasm and vacuole shrink
...
If two cells are next to each other, water will move from the cell with a higher water potential
to the cell with a lower water potential by osmosis
...
Transpiration - loss of water vapour from the aerial parts of a plant mostly through
stomata in the leaves
...
Evaporation is limited by the waxy cuticle
...
As photosynthesis only occurs
when it's light, most water is lost during the day
...
Water enters leaf through xylem and moves into cells of spongy mesophyll
...
Water evaporates from cell walls of spongy mesophyll
...
Water vapour moves by diffusion out of leaf through stomata
...
This is
called the water vapour potential gradient
...
Transpiration is essential for plants to survive
...
This movement:
transports useful mineral ions up the plant
maintains cell turgidity
supplies water for growth, cell elongation and photosynthesis
supplies water that can keep the plant cool on a hot day
Environmental factors that affect transpiration rate:
Light intensity - in light, stomata open to allow gaseous exchange
...
Temperature - higher temperature increases the rate of transpiration:
o increases rate of evaporation from cell surfaces so water vapour potential in
the leaf rises
o increases rate of diffusion through stomata because water molecules have
more kinetic energy
o decreases relative water vapour potential in air allowing more rapid diffusion
of molecules out of the leaf
Relative humidity - higher humidity in the air decreases rate of water loss because
there is a smaller water vapour potential gradient between the leaf and the air outside
...
Stomata close and the leaves wilt
...
It measures rate of water uptake
by a shoot
...
The movement of the meniscus at the end of the water column can be measured
...
To make sure results are valid:
set it up under water to ensure there are no air bubbles
ensure the shoot is healthy
cut the stem under water to prevent air entering xylem
cut the stem at an angle to provide a large surface area in contact with the water
dry the leaves
The volume of the capillary tube must be calculated using the area of the circle x length of
the tube
...
Rate = volume/time
...
Cohesion - the attraction between water molecules caused by H bonds
...
The outermost layer of cells (epidermis) of a root contains root hair cells with long extensions
(root hairs) that increase the surface area
...
Mineral ions are actively absorbed, making the water potential of the cytoplasm more
negative
...
Mineral ions are actively transported into the medulla
making the water potential more negative so water follows by osmosis
...
The role of the endodermis:
The movement of water across the root is driven by an active process that occurs at the
endodermis, a layer of cells surrounding the medulla and xylem
...
The Casparian strip blocks the apoplast pathway between the cortex and the medulla
...
The membrane contains transporter proteins which actively pump mineral
ions from the cytoplasm of the cortex cells into the medulla and xylem
...
Once the water has entered the medulla, it cannot pass back into the cortex as the apoplast
pathway of the endodermal cells is blocked by the Casparian strip
...
Processes that help move water up the stem:
Root pressure:
The action of the endodermis moving minerals into the medulla and xylem by active transport
draws water into the medulla by osmosis
...
Transpiration pull:
The lost water from the leaves must be replaced by water coming up from the xylem
...
As molecules are lost at the top of the column, the whole column is
pulled up as one chain
...
Xylem must be
strengthened with lignin to prevent the vessel from collapsing under tension
...
Capillary action:
Adhesion forces attract water molecules to the sides of the xylem vessels
...
Most water that leaves the leaf exits as vapour, and only a tiny amount leaves through the
waxy cuticle
...
This lowers water potential in these cells causing water to enter them from
neighbouring cells
...
Hydrophyte - a plant adapted to living in water or in wet ground
...
Stomata must be open during the day, however this leaves an easy route for water to be lost
...
Plants living on land must be adapted to:
reduce this loss of water
replace the water that is lost
Most terrestrial plants can reduce their water losses by structural and behavioural adaptions:
waxy cuticle on the leaf reduces water loss due to evaporation through the epidermis
stomata often found on the under surface of leaves, reducing evaporation due to direct
heating from the sun
stomata closed at night when there is no light for photosynthesis
deciduous plants lose their leaves in winter when the ground may be frozen (making
water less available) and when temperatures may be too low for photosynthesis
Marram grass specialises in living on sand dunes
...
Marram grass is a xerophyte
...
The air becomes humid which
reduces water loss from the leaf
...
There is a thick waxy cuticle on the outer side of the rolled leaf to reduce evaporation
...
The stomata are in pits in the lower epidermis which is also folded and covered in
hairs
...
The spongy mesophyll is dense with few air spaces so less surface area is available
for evaporation of water
...
The stem is often ribbed so
it can expand when water is available
...
The stem is green for photosynthesis
...
Other xerophytic features:
closing stomata when water availability is low
maintaining high salt concentration in cells to create low water potential, reducing
evaporation of water from the cell surfaces as the water potential gradient between
cells and leaf air spaces is reduced
long tap root that can reach deep underground water
Hydrophytes are plants that live in water e
...
water lilies
...
Adaptations of a water lily:
many large air spaces in the leaf, keeping leaves afloat
stomata on the upper epidermis to allow gaseous exchange
large air spaces in the leaf stem, helping with buoyancy and allowing oxygen to
diffuse quickly to the roots for aerobic respiration
Transpiration is the loss of water vapour from the surfaces of the leaves but the water will not
evaporate into water or air with high humidity
...
Many plants contain specialised structures at the
tips of their leaves called hydathodes
...
Assimilates - substances that have become a part of the plant
...
g
...
Source - a part of the plant that loads materials into the transport system, e
...
leaves
...
Translocation occurs in the phloem and is the movement of assimilates, substances made by
the plant using substances absorbed from the environment
...
Sucrose is loaded into the sieve tube by
an active process, involving use of
energy from ATP in the companion
cells
...
This increases their concentration
outside the cells and decreases their
concentration inside the companion
cells
...
These
proteins only allow H+ ions back into
the companion cells if they are accompanied by sucrose molecules
...
It is also called secondary active transport, as it results from the active transport
of the H+ ions out of the cells and moves sucrose against its concentration gradient
...
Movement of sucrose along the phloem is by mass flow
...
The solution is called sap and can flow upwards or
downwards as required
...
Water enters the tube at the
source, increasing the pressure, and leaves at the sink, reducing the pressure
...
Sucrose entering the sieve-tube element lowers the water potential, therefore water molecules
move into the sieve-tube element by osmosis from surrounding tissues
...
A source is any part of the plant that loads
sucrose into the sieve tubes
...
During spring,
summer and autumn, the leaves are the biggest
source, as sugars made from photosynthesis are
loaded into the phloem sieve tubes
...
The sucrose could be used for
respiration or growth in a meristem, or converted
to starch for storage
...
It can also be removed by
active transport
...
This reduces the hydrostatic pressure in the
phloem at the sink
...
1
Pathogen – microorganism that causes disease
...
A host body is a good habitat for
microorganisms to live, so there are many types of pathogens that live in or on the body
...
Bacteria cells are smaller than eukaryotic cells but can reproduce rapidly
...
In plants, the bacteria
often live in the vascular tissues and cause them to die
...
The fungus can send out specialised
reproductive hyphae which grow to the surface of the skin to release spores
...
In plants the fungus often lives in vascular tissue where it can gain nutrients
...
Viruses cause many diseases in both plants and animals
...
They cause the cell to manufacture more copies of
the virus
...
Protoctists cause harm by entering host cells and feeding on the contents as they grow
...
Tuberculosis
Bacterial meningitis
Ring rot (plants)
Black sigatoka (bananas)
Ringworm (cattle)
Athlete’s foot (humans)
HIV/AIDS
Influenza
Tobacco mosaic virus
Blight (tomatoes/potatoes)
Malaria
disease affects many body parts, killing the cells and tissues
infection of the meninges (membranes that surround brain
and spinal cord); membranes become swollen and may cause
severe brain or nerve damage
ring of decay in the vascular tissue of potato tuber or tomato
causes leaf spots on banana plants, reduces yield
growth of fungus in skin with spore causes erupting through
skin to cause a rash
growth under skin of feet
attacks cells in immune system, compromises immune
response
attacks respiratory system, causes muscle pain and headaches
causes mottling and leaf discoloration
affects leaves and potato tubers
parasite in blood causes headache, fever and may lead to
coma and death
Direct transmission – passing a pathogen from host to host with no intermediary
...
Transmission – passing a pathogen from infected to uninfected individual
...
Pathogens have a life cycle:
travel from one host to another (transmission)
enter host’s tissues
reproduce
leave host’s tissues
Pathogens can be transmitted between animals in many ways
...
Means of transmission
Factors that affect transmission
Direct physical contact e
...
touching an
Hygiene: washing hands regularly,
infected person or contaminated surfaces
...
condoms
...
Examples: cholera, food poisoning
...
Droplet infection, where the pathogen is
Cover mouth when coughing/sneezing,
carried in water droplets in the air
...
of correctly
...
Examples: anthrax, tetanus
...
Other factors that affect transmission include social factors:
overcrowding – many people living and sleeping together in one house
poor ventilation
poor health
poor diet
homelessness
living/working with people migrated from areas where disease is more common
Some pathogens are transmitted indirectly via a vector
...
Many pathogens are present
in soil and infect plants by entering the roots
...
These
spores may be carried in the wind (airborne transmission)
...
Pathogens in leaves are distributed when leaves are shed and
carry the pathogen to infect another plant
...
Indirect transmission of plant pathogens often occurs as a result
of insect attack
...
When the insect attacks another plant, the pathogen is transmitted
...
Many protoctists, bacteria and fungi can grow and reproduce more rapidly in warm/moist
conditions
...
There is therefore a
greater variety of diseases in warmer climates, and animals or plants living here are more
likely to become infected
...
Plants manufacture sugars, which represent a rich source of nutrients for many bacteria,
fungi, protoctists, viruses, insects and vertebrates
...
Plants do not have an immune system like animals, but have developed a wide range of
defences, including passive defences to prevent entry and active defences that are induced
when the pathogen is detected
...
Some of these chemicals are present before
infection, however because production of chemicals requires a lot of energy, many are not
produced until the plant detects an infection
...
The
plant responds by fortifying the defences already present
...
A few cells are scarified to save the plant
...
Brought about by intracellular enzymes that are activated by
injury
...
Causes death of the cambium tissue in
the bark
...
Mucous membrane – specialised epithelial tissue covered by mucus
...
The mechanisms that have evolved to prevent entry of pathogens are called primary defences
...
The skin is the main primary defence
...
Most of these cells are called keratinocytes
...
They then migrate to the surface of the skin
...
This is called keratinisation
...
When the skin is damaged, the body must prevent excess blood loss by forming a clot, a
temporary seal to prevent infection
...
These factors activate an enzyme
cascade
...
This makes a temporary seal
under which the skin is repaired
...
Stem cells in the epidermis
divide by mitosis to form new cells which migrate to the edges of the cut and differentiate to
form new skin
...
The tissues contract to help draw the edges of the cut together
...
Substances such as oxygen and nutrients in food must enter the blood
...
The air and
food we take in may contain microorganisms, therefore the airways, lungs and digestive
system are at risk of infection
...
The epithelial layer contains mucussecreting cells called goblet cells
...
In the airways, the mucus lines the passages and traps any pathogens in the air
...
The cilia move in a coordinated way to waft the layer
of mucus along
...
It then enters the stomach where any pathogens are killed by the stomach acid
...
These reflexes include coughing, sneezing and vomiting
...
Inflammation is a sign that tissue is infected
...
They release a cell signalling substance called histamine
...
The main
effect is to cause vasodilation and make capillary walls more permeable to white blood cells
...
Excess tissue fluid is drained into the lymphatic system
where lymphocytes are stored
...
Other primary defences:
eyes protected by antibodies and enzymes in tear fluid
ear canal lined with wax that traps pathogens
female reproductive system protected by a mucus plug in the cervix and by
maintaining acidic conditions in the vagina
Antigen-presenting cell – a cell that isolated the antigen from a pathogen and places it
on the plasma membrane so it can be recognised by other cells in the immune system
...
Cytokines – hormone-like molecules used in cell signalling to stimulate the immune
response
...
Opsonins – proteins that bind to the antigen on a pathogen and allow phagocytes to
bind
...
A pathogen is
recognised as foreign by the antigens on its outer membrane
...
Opsonins are proteins that attach to the antigens on the surface of a pathogen
...
Some opsonins are not specific so can attach to a variety of pathogens
...
The first line of secondary defence is phagocytosis
...
The most common phagocytes are neutrophils
...
They
travel in the blood and tissue fluid
...
They contain lysosomes, and engulf and digest pathogens
...
Dead neutrophils may collect to form pus
...
They travel in the blood as
monocytes before settling in the body tissues
...
Dendritic cells (type of macrophage) are found in the peripheral
tissue
...
When a
macrophage engulfs a pathogen, it does not fully digest it; it saves the antigens and the cell
becomes an antigen-presenting cell
...
The
special protein complex ensures the cell is not mistaken for foreign and attacked
...
These are T and B lymphocytes
...
Activation of the specific B and T cells is called clonal selection
...
The series of events is stimulated by chemicals called cytokines
...
B memory cells – cells that remain in the blood for a long time, providing long term
immunity
...
Interleukins – signalling molecules used to communicate between different white
blood cells
...
T helper cells – cells that release signalling molecules to stimulate the immune
response
...
T memory cells – cells that remain in the blood for a long time, providing long term
immunity
...
The specific immune response involves B and T lymphocytes
...
The immune
response produces antibodies
...
The immune response
also provides long-term protection from the disease
...
The specific immune response:
T lymphocytes differentiate into four types of cell:
T helper cells – release cytokines that stimulate the B cells to develop
T killer cells – attack and kill host-body cells that display the foreign antigen
T memory cells – provide long term immunity
T regulator cells – shut down the immune response after the pathogen has been
removed; also involved in preventing autoimmunity
B lymphocytes develop into two types of cell:
plasma cells – circulate in the blood, manufacturing and releasing the antibodies
B memory cells – remain in the body for years and act as the immunological memory
Communication of cells is called cell signalling
...
There are many signalling molecules each performing a different role
...
Examples of cell signalling:
Macrophages release monokines
...
T cells and macrophages release interleukins which can stimulate the clonal
expansion and differentiation of B and T cells
...
An autoimmune disease occurs when the immune system attacks a part of the body
...
The causes are unknown but include both genetic and
environmental factors
...
Anti-toxins – antibodies that render toxins harmless
...
Primary immune response – initial response caused by a first reaction
...
Antibodies are immunoglobulins – complex proteins produced by the plasma cells in the
immune system
...
They have a region with a
specific shape that is complementary to that of a specific antigen
...
Antibodies attach to antigens
and make them harmless
...
How antibodies work:
Opsonins – a group of antibodies that bind to the antigens on a pathogen and act as
binding sites for phagocytic cells so these can more easily bond and destroy the
pathogen
...
The pathogen may have
another use for this antigen molecule e
...
a binding site used for attachment to a host
cell
...
Agglutinins – as each antibody has two identical binding sites it can crosslink
pathogens
...
Anti-toxins – some antibodies bind to molecules released by pathogenic cells
...
Antibodies are produced in response to
infection
...
This is the
primary immune response
...
Antibodies do not stay in the blood
...
This is the secondary immune response
...
Active immunity – where the immune system is activated and manufactures its own
antibodies
...
Artificial immunity – immunity achieved as a result of medical intervention
...
Epidemic – rapid spread of disease through a high proportion of the population
Vaccination – way of stimulating an immune response so immunity is achieved
...
It is usually injected
...
The antigenic material can take a variety of forms:
whole, live microorganism (smallpox)
harmless or attenuated (weakened) pathogen (measles)
dead pathogen (cholera)
preparation of the antigens from a pathogen (hepatitis B)
a toxoid (harmless version of a toxin) (tetanus)
Herd vaccination is using a vaccine to provide immunity to almost all the population at risk
...
It is essential to vaccinate almost all the population
...
This involves vaccinating
all people in the immediate vicinity of the new case, e
...
the town/village or surrounding
houses
...
However, some pathogens can undergo genetic mutations which change their antigens
...
Some pathogens such as the
influenza virus, are unstable and regularly undergo antigen changes
...
Influenza (flu) is a killer disease caused by a virus
...
Occasionally a new strain of the virus can cause an epidemic
...
Types of immunity:
Natural
Active
immunity provided by antibodies made in the
immune system because of infection; a person
suffers from the disease once and is then
immune
Passive
antibodies provided via placenta or breastmilk,
making the baby immune to diseases the
mother is immune to; useful in the first year of
the baby’s life however is not long lasting
Artificial
immunity provided by
antibodies made in the
immune system due to
vaccination
immunity provided by
injection of antibodies
made by another individual
Antibiotic – chemical that prevents the growth of microorganisms
...
Synthetic biology – re-engineering of biology
...
It is a fungus that
releases compounds to kill bacteria
...
Traditional remedies – many drugs have been used for centuries
...
It was used as an anaesthetic, as it
reduces nervous action in the CNS
...
Willow-bark extract has been used to relieve pain and fever for a long time
...
Observation of wildlife – many animals make use of medicinal plants
...
Birds
line their nests with medicinal leaves to protect chicks from mites
...
The molecules can be analysed and similar ones
manufactured
...
Many use receptors on plasma
membranes, e
...
HIV binds to receptors on the surface of T helper cells
...
The glycoprotein receptor molecules can be isolated
and sequenced
...
A drug must be found to mimic the shape
of the receptor and could be used to bind to the virus, blocking it from entering the T
helper cell
...
Once the technology has developed, it may be possible to sequence the genes from
individuals with a particular condition and develop specific drugs
...
Another is to design and construct new devices and systems that may be
useful in research or healthcare
...
Antibiotic use and abuse – overuse and misuse of antibiotics have enabled
microorganisms to develop resistance
...
Some bacteria such as MRSA are known for their resistance
to a range of antibiotics
...
2
Biodiversity – measure of the variation found in the living world
...
Species – group of organisms that can interbreed to produce fertile offspring
...
The range of habitats in which
different species live is called the habitat diversity
...
A species consists of individual organisms that are similar in appearance, anatomy,
biochemistry and genetics
...
The range
of organisms in a habitat contributes to the species diversity
...
A habitat is more diverse if the
species are more evenly represented
...
The
degree to which the species are represented is known as the species evenness
...
This can create
breeds in a species e
...
in dogs
...
You can
sample a habitat, i
...
select a small portion and study it carefully, then multiply up to estimate
the number in the whole habitat
...
This can be
done by using randomly
generated numbers for
coordinates and then
using a GPS to find that
exact position
...
May
deliberately sample an
area that contains a
particular species
...
Systematic
When samples are taken
at fixed intervals across
Advantages
Ensures data
is not biased
by selective
sampling
...
Disadvantages
May not cover all
areas equally
...
Data may be
biased; presence of
large/colourful
species may entice
researcher, leading
to overestimate of
biodiversity
...
are sampled
and species
are not underrepresented
...
Line and belt
transects are systematic
techniques
...
be recorded, others
might be missed
leading to
underestimation of
biodiversity
...
to record
key to identify plants
camera to record specimens
When visiting a site to measure biodiversity it is best to use a range of techniques
...
Any sampling should cause as little disturbance as possible
...
A quadrat is a square frame used to define the size of a sample area
...
It may be possible to estimate the percentage cover of each species
...
You lower the frame into the quadrat and record any plants touching the needles
...
Therefore, each plant touching a needle has 1% cover
...
You stretch a long string across the habitat and take
samples along the line
...
You could also use a quadrat at set
intervals along the line (interrupted belt transect)
...
You can also use a continuous belt transect
...
This provides quantitative data in a band across the habitat
...
Ecologists often rely on these signs
to estimate population sizes
...
This provides a more accurate way to calculate the population size
...
Any small animals such as insects will get caught in the
net
...
You can collect from trees by placing a sheet of paper under a branch and shaking it
...
It consists of a small container
buried in the soil
...
The trap should
contain water or paper to stop the animals crawling out
...
You place
leaf litter in a funnel and a light above the litter drives the animals downwards as it
dries out and warms up
...
A light trap can be used to attract insects in the dark; they fly towards the light and
eventually fall into the collecting vessel under the light that contains alcohol
...
Small mammals can be
trapped using a Longworth trap
...
capture a sample of animals
mark each individual in some way; the number captured is C1
release marked animals and leave traps for another period of time
the number captured on the second occasion is C2
the number of already marked animals captured on the second occasion is C3
total population = ( C1 x C2 ) / C3
However the estimate can be affected by animals that learn the trap is harmless and contains
food, or animals who do not like the experience and avoid traps after the first capture
...
Locus – position of a gene on a chromosome
...
Simpson’s index of biodiversity – a measure of the diversity of a habitat
...
Species richness – measure of how many different species are present
...
A habitat in which there are even numbers of individuals in each species is likely to
be more diverse than one which individuals of one species outnumber all others
...
To
measure species evenness, you need to carry out a quantitative survey
...
To survey the frequency of plants, record % cover of each plant species
...
To measure population of small animals such as insects in living in the soil, the
only way is to use handfuls of soil and sift through it
...
Simpson’s index of diversity is a measure of the diversity of a habitat
...
It is calculated by:
D = 1 – [∑(n/N)2]
where n is the number of individuals of a species (or % cover for plants) and N is the total
number of all individuals of all species (or total % cover)
...
Here, a small change to the environment may affect
one species
...
The habitat tends to be more
stable and able to withstand change
...
In this case, a small
environmental change that affects one of these species could destroy the whole habitat
...
Isolated populations, such as zoo animals, may be small, therefore their genetic diversity is
limited
...
Genetic diversity is found where there is more than one allele for a
locus
...
It means
there are more genetic differences between the gametes produced by members of the
population
...
This does not give a good measure of the value of the
population as a genetic resource
...
Some loci have more than two alleles
and are called polymorphic gene loci
...
Climate change – significant, long-lasting changes in weather patterns
...
The human population is having a greater and greater effect on other species:
we have learned to use the environment to our advantage
we alter ecosystems to provide ourselves with food
we destroy and fragment habitats
we are using more of Earth’s resources
we pollute the atmosphere
We often harm other species (directly or indirectly) and this can lead to extinction
...
By clearing vegetation we
reduce the size of habitats and population sizes of species living in those habitats
...
This means the species has less capacity to adapt
to changing conditions through evolution
...
A
monoculture is a crop consisting of one strain of the species (limited genetic diversity)
...
Selective breeding reduces genetic diversity because
farmers select traits such as rapid growth
...
Genetic diversity declines
...
Loss of these varieties
reduces the genetic diversity of the species (genetic erosion)
...
Species with less variation due to loss of genetic
diversity are less able to adapt to changes in temperature and rainfall
...
However there are
obstructions to migration:
major human developments
agricultural land
large bodies of water
mountain ranges
Domesticated plants/animals are at risk as they have little variation due to selective breeding
...
The efficiency of agriculture will decline and less food
will be available
...
The rate of extinction is rising dramatically
...
For example, when the
dinosaurs became extinct
...
Soil depletion – loss of soil fertility caused by removal of minerals by continuous
cropping
...
All organisms in a habitat are linked in
a food chain/web
...
When one species is affected by human activity and its numbers decline, this will
affect other species
...
The decline of a keystone species will have a dramatic effect on the
habitat
...
Many plants are keystone species
...
g
...
They may have a small population but the dams
have a huge effect on the habitat
...
Genetic resource:
Wild animals and plants have evolved to hold answers to problems caused by climate
change
...
By breeding from wild strains and species, we may be able to breed new crop
varieties that can cope with the new conditions created by climate change
...
Plants have evolved a wide range of molecules that combat diseases, and fungi have
evolved molecules that help them compete with bacteria in the soil
...
It is important to maintain the genetic diversity of wild species because of
their potential
...
One of the most immediate effects that loss of
biodiversity has on food production is depletion of soil
...
This is due to crops taking
minerals out of the soil so when the crop is harvested, the minerals are removed from
the ecosystem
...
The effects of soil depletion were shown in the 1930s in America
...
Aesthetic reasons to maintain diversity:
People experience feelings of joy when observing nature
...
Landscapes are formed by action of climatic factors on the land
...
Diverse tropical forests protect the soil from factors
such as rainfall that could erode and wash away exposed soils
...
The trees take up water and the organic matter in the
soil holds water
...
The water that
collects in forested hills will slowly drain away and supply water elsewhere
...
Deforestation has
been linked to severe flooding
...
Rainfall drains more quickly and there is more run-off
...
The soil is deposited where the
water flow is reduced and further reduces the drainage
...
Conservation in situ – carrying out active management to maintain the biodiversity in
the natural environment
...
Wildlife reserves – areas set aside for the conservation of species or habitats
...
It involves minimising
the human impact on the natural environment and protecting it
...
However, it can be difficult to persuade countries
that legislation is necessary
...
Wildlife reserves are designated areas established for the conservation of habitats and
species
...
The principles for choosing a wildlife reserve must include:
o Comprehensiveness – how many species are represented in the area and what
are the current environmental conditions?
o Adequacy – is the area large enough to provide for long term survival of all
the species, populations and communities represented?
o Representativeness – is there a full range of diversity within each species and
each set of environmental conditions?
Conservation does not mean excluding human activity
...
In the past reserves have been set up that do not meet
these needs, and there has been conflict due to:
o protected animals coming out of the reserve to raid crops
o people continuing to hunt protected animals for food
o illegal harvesting of timber and other plant products
o tourists feeding protected animals or leaving litter
Various bodies in the UK conserve and enhance the natural environment:
o National Parks – areas of protected countryside that everyone can visit
...
o Sites of Special Scientific Interest (SSSIs) – the country’s best wildlife and
geological sites
...
o Marine conservation zones – areas important to conserve the biodiversity of
nationally rare and threatened habitats and species in our seas
...
In the UK, numbers of otters are
increasing in new reed beds
...
This was a start towards recreating the
rich mammal community that existed in the region before European colonisation
...
Zoos play an important role in conservation
...
Modern
reproductive technologies such as freezing sperm, eggs or embryos can preserve genetic
material
...
Some zoos carry out research on domestic species similar to
the target species
...
Advantages of ex situ conservation:
organisms are protected from predation and poaching
health of individuals can be monitored and medical assistance given as required
populations can be divided so if a disaster strikes one, the other survives
genetic diversity of the population can be measured
selective breeding can be carried out to increase genetic diversity
modern reproductive technology such as IVF can be used to increase chances of
reproductive success
...
The conservation of
plants is easier than that of animals:
as part of their life cycle, most plants naturally have a dormant stage (the seed)
as seeds are produced in large numbers they can be collected from the wild without
causing disturbance to the ecosystem or damaging the wild population
the seeds can be stored and germinated in protected surroundings
seeds can be stored in huge numbers without taking up much space
plants can be bred asexually
the botanic garden can increase the numbers of individual plants quickly through
techniques such as tissue culture which provides a supply for research or for
reintroduction to the wild
However, there are problems:
funding a botanic garden can be difficult; fewer people are willing to sponsor plants
(instead of animals)
collecting wild seeds causes disturbance
collected samples may not have a representative level of genetic diversity
seeds collected from one are may be genetically different from those collected
elsewhere and may not succeed in a different area
seeds stored for any length of time may not be viable
plants bred asexually will be genetically identical, reducing genetic diversity
conclusions from research based on a small sample may not be valid for the whole
species
A seed bank is a collection of seed samples
...
These will include examples of the rarest species
...
However, the
seeds are used to provide a wide range of benefits to humanity, such as providing seeds for
food crops, building materials for communities and disease-resistant crops for agriculture
...
To prolong their viability, seeds are stored in dry or freezing conditions
...
For every 1%
decrease in seed moisture level, the life span doubles
...
Scientists at the Millennium Seed Bank carry out
germination tests each year
...
Germination rates are monitored and
research into physiology of seed dormancy and germination is carried out
...
CITES – the Convention on International Trade in Endangered Species
...
The loss of habitats and increasing number of endangered species needs a worldwide
solution
...
The aim is to ensure
international trade in specimens of wildlife does not threaten their survival
...
trade does not endanger the survival of populations in the wild
o ensure trade in wild plants for commercial purposes is prohibited
o ensure trade in artificially propagated plants is allowed, subject to permit
o ensure some less endangered wild species may be traded subject to a permit
International trade policies can be hard to enforce; where there is demand for a
product there will be attempts to supply it
...
It is dedicated to promoting sustainable development
...
It states that the partner states must adopt ex situ conservation facilities to
complement in situ measures
...
Different parks specialise in breeding different animals
...
Time, expense and
distress to rare animals can be reduced by importing genetic material, i
...
transporting
sperm, eggs or embryos and using artificial insemination or IVF techniques
...
Plant-breeding programmes can be enhanced by sharing stored specimens
...
These
partners duplicate the collections in case of disaster
...
Many governments make
agreements with local land owners and tenants, designed to enhance the biodiversity and
conservation value of land at a local level
...
Farmers and land managers were paid to
enhance and conserve landscapes
...
The aims were:
o improve natural beauty and diversity of the countryside
o enhance, restore and re-create targeted landscapes, their wildlife habitats and
historical features
o improve opportunities for public access
The Environmental Stewardship Scheme replaced it in 2005
...
The aim is to provide funding and advice to help them conserve, enhance and
promote the countryside by:
o looking after wildlife, species and their habitats
o ensuring land is well managed and retains its traditional character
o protecting historic features and natural resources
o ensuring traditional livestock and crops are conserved
o providing opportunities for people to visit and learn about the countryside
Classification and Evolution 4
...
Classification – the process of placing living things into groups
We classify living things because:
it is convenient
it makes the study of living things more manageable
it makes it easier to identify organisms
it helps us see the relationships between species
The current system of classification:
Domain – the highest taxonomic rank; there are three domains – archaea, eubacteria
and eukaryotae
...
Phylum – major subdivision of kingdom, contains all the groups of organisms that
have the same body plan e
...
backbone
...
g
...
Order – subdivision of the class using additional information e
...
meat eating and
vegetation eating animals
...
g
...
Genus – a group of closely related species
...
The Chordata have a nervous system with a central bundle of nerves running along their
back, protected by a series of bones called the vertebral column – these are vertebrates
...
As you descend into lower taxonomic groups it becomes increasingly difficult to separate
closely related species and to place a species accurately
...
Binomial means ‘two names’
...
g
...
The genus name is always given a capital letter
...
g
...
sapiens
...
Carl Linnaeus devised the binomial system
...
Using a common name
doesn’t work well because:
the same organism may have a different common name in different parts of a country
different common names are used in different countries
translation of languages or dialects may give different names
the same common name may be used for different species in other parts of the world
The biological definition of a species is: ‘a group of organisms that can freely interbreed to
produce fertile offspring’ however this definition does not work for organisms that reproduce
asexually and is hard to apply to organisms that are only known as fossils
...
Members of a species occupy the same niche in an ecosystem
...
In early attempts at classification,
Aristotle classified all living things as either plant or animal, and then subdivided the animals
into three groups:
live and move in water
live and move on land
move through the air
This was based on similarities he observed; some animals have fins, some have legs and
some have wings
...
In the 17th century, microscopes revealed further details inside cells
...
Also, fungi used to be classified as a plant because their hyphae grow into the surrounding
substrate in the same way as roots
...
They digest
organic matter and absorb the nutrients like animals
...
These kingdoms are
now based on observable features of anatomy but at a microscopic level
...
It is possible two unrelated species could adapt in
similar ways and look very similar (convergent evolution)
...
Evidence from biological molecules can help determine how closely related two species are
...
Organisms with very different versions of the molecules are less closely
related
...
However, it is not
identical in all species
...
DNA is another biological molecule found in all living organisms
...
These occur at random
...
The more similar, the more closely
related the species
...
Carl Woese suggested the three-domain classification system based on detailed study of the
ribosomal RNA gene
...
This division
was based on the fact that Bacteria are fundamentally different from the Archaea and the
Eukaryotae
...
Phylogeny – the study of the evolutionary relationships between organisms
...
This may
help make conservation more successful
...
The time when the two
species started to evolve separately is a branch point on the evolutionary tree
...
Phylogeny is the study of evolutionary relationships between species
...
Using the evolutionary tree, we can see certain evolutionary relationships that indicate how
closely related species are:
1
...
we have a common ancestor in the recent past
3
...
humans and gorillas can be classified in the same taxonomic group
5
...
the common ancestor shared by the thrush and snake is more recent than the common
ancestor shared by the thrush and mammals
7
...
similarly, the snake is more closely related to the thrush than the frog or trout
9
...
Darwin proposed the idea of natural selection
...
Many species were like
those found on South American mainland
...
Darwin concluded that one species had arrived on
the islands from the mainland and then had evolved to form many different species
...
Their first
publications were joint papers about evolution by natural selection
...
As all the offspring are different, some may be better adapted than others and are
more likely to survive and reproduce, passing on their characteristics to the next generation
...
The greater the number of
similarities between the gene sequences, the more closely related the species
...
Comparison of
human DNA with that of other organisms shows:
1
...
6% is different from that of gorillas
6
...
During sexual reproduction
mitochondria contained in the egg are passed to the offspring, therefore mDNA is passed on
from the mother
...
mDNA mutates more
frequently than nuclear DNA so there is lots of variation in the sequence of mDNA between
people in different parts of the world
...
Continuous variation – variation where there are two extremes and a full range of
values in between
...
Environmental variation – variation caused by response to environmental factors such
as light intensity
...
Interspecific variation – differences between species
...
Variation – differences between individuals
...
These differences are
known as intraspecific variation
...
Continuous variation:
most individuals close to the mean
number of individuals at the extremes is low
often regulated by more than one gene
can be influenced by the environment
Examples: height, length of leaves, length of stalk, number of flagella on bacterium
...
Discontinuous variation:
members of a species may be evenly distributed or not
usually regulated by a single gene
not influenced by the environment
Examples: gender, blood group, presence of flagella or not
...
Inherited/genetic variation - genes we inherit from parents define characteristics
...
g
...
Combined effects – many characteristics are affected by both causes of variation:
in the past century, humans have grown taller as a result of a better diet, however you
are unlikely to grow tall if your family are short because the height you can reach is
limited by your genes
not all our genes are active at any one time, e
...
at puberty many changes occur in the
body because different genes are becoming active
changes in the environment can directly affect which genes are active
Correlation coefficient – a measure of how closely two sets of data are correlated
...
Standard deviation – measure of the spread around a mean
...
Standard deviation is a measure of variation:
low SD indicates the data has a narrow range and the points are closely grouped to the
mean; this can indicate reliability
high SD indicates the data points have a larger range and are less well grouped; this
may indicate lower reliability
The Student’s t-test is used to compare two means, and tests whether the difference between
them is significant
...
Degrees of freedom are defined as the number of values in a statistical calculation that are
free to vary
...
In the t-test there
are two data sets so the number of degrees of freedom is (n1 + n2) – 2
...
We consider the 5% significance level
...
A correlation coefficient is used to consider the relationships between two sets of data
...
We can use a table of critical values to assess whether the value or r s indicates correlation
...
Adaptation – a characteristic that enhances survival in the habitat
...
Behavioural adaptations – ways behaviour is modified for survival
...
Variation that helps an organism survive is an adaptation
...
A well-adapted organism will be able to:
find enough food or photosynthesise well
find enough water
gather enough nutrients
defend itself from predators and diseases
survive the physical conditions of its environment such as temp
...
Marram grass must be adapted to take up as much water as possible and to avoid
losing that water
...
Any structure that enhances the survival of an organism is an adaptation
...
Enables the plant to absorb a lot of water when it is
available; helps to stabilise the sand dunes
...
Lower epidermis covered in hairs
Reduces air movement so water vapour is retained
close to the lower epidermis
...
Low density of stomata
Fewer stomata mean less water vapour is lost
...
A behavioural adaptation is an aspect of the behaviour of an organism that helps it survive
...
This helps reduce transpiration
...
A physiological/biochemical adaptation ensures correct functioning of cell processes
...
Despite separate evolution and being unrelated, marsupial moles and placental moles share
many characteristics and look very similar
...
How natural selection works:
mutation creates alternative versions of a gene (alleles)
this creates genetic variation between the individuals of a species (intraspecific)
once variety exists, the environment can select; when resources are scarce, the
environment will select those variations that give an advantage – there is a selection
pressure
individuals with advantageous characteristics will survive and reproduce
they pass on their genes so the next generation will have a higher proportion of
individuals with the successful characteristic
over time, the group will become well adapted to its environment (adaptation)
An insecticide applies a very strong selection pressure on insects
...
If it has some form of resistance, it may survive
...
The
resistance quickly spreads through the population
...
Mosquitoes have developed
resistance and have evolved to produce an enzyme that can break down the
pyrethroids
...
Insect populations have become resistant
...
As a result,
the shape is no longer complementary to the shape of the pesticide molecules
...
When insects become resistant to pesticides it can cause the pesticide to accumulate in the
food chain
...
However, DDT has been banned now in many areas
...
When they are taken, most of
the bacteria are killed, however there may be a few who are resistant
...
Some bacteria have gained a particularly wide range of resistance
...
Medical
researchers are struggling to develop new and effective drugs but the bacterial populations
become resistant to them
Title: Biology AS Level OCR A Revision Notes (full AS course - new spec for 2017)
Description: Full AS course for OCR Biology A - Revision Notes (new spec) with diagrams :)
Description: Full AS course for OCR Biology A - Revision Notes (new spec) with diagrams :)