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(g) The ultrastructure of eukaryotic cells and the functions of the different cellular components
Nucleus  controls cell activity, transmits genetic information & houses all of the cell’s genetic
material in the form of DNA, which contains the instructions for protein synthesis
...
It doesn’t have a membrane around it
...
It separates
the content of the nucleus from the rest of the cell
...
At these points, some dissolved substances & ribosomes can pass
through
...
Substances, such as some steroid hormones, may enter the nucleus, from the
cytoplasm via these pores
...
When the cell
is not dividing, chromatin is spread out or extended
...
These make up nearly all the organism’s genome
...

Rough Endoplasmic Reticulum (RER)  It is coated with ribosomes
...
It provides a large surface area for ribosomes, which assemble amino
acids into proteins
...

Smooth Endoplasmic Reticulum (SER)  associated with the synthesis, storage & transport of
lipids & carbohydrates
...
SER contains enzymes that catalyse
reactions involved with lipid metabolism, such as: synthesis of cholesterol, synthesis of
lipids/phospholipids needed by the cell, synthesis of steroid hormones
...
It modifies proteins
received from the RER & then packages them into vesicles so they can be transported
...
The proteins are packaged into vesicles that
are pinched off &then stored in the cell or moved to the plasma membrane, either to be
incorporated into the plasma membrane or exported outside the cell
...
They do not have a membrane
...
They’re a spherical shape &
they are self-replicating – more can be made if the cell’s energy needs increase
...
Also, lysosomes can engulf
old cell organelles &foreign matter, digest them &return the digested components to the cell for
reuse
...


Plasma membrane  controls the entry & exit of substances into & out of the cell
...
Centrioles are
involved in the organisation of microtubules that make up the cytoskeleton
...
E
...
wave mucus along trachea or make sperm swim
...

Explain why organelles such as mitochondria do not always look the same size and shape
...


(i)
1)
2)
3)
4)
5)
6)
7)

The interrelationship between the organelles involved in the production and
secretion of proteins
The gene containing the instructions for the production of the hormone is copied onto a
piece of mRNA
...
The types of protein fibres are:
• Microfilaments (small solid strands made of actin, 7nm diameter)
• Microtubules (protein cylinders made of tubulin molecules, 25nm diameter)
Their functions include:
• Supporting organelles
• Strengthening the cell and maintaining cell shape
• Transporting materials within in the cell (e
...
the spindle during mitosis)
• Cell movement (cilia and flagella)
Microtubules do not move, but they provide an anchor for protein to move along
...
g
...
Using ATP it ‘swivels’,
pushing the organelle along
...

Flagella and cilia are each made from a cylinder containing 9 microtubules
...
When a molecule of dynein ‘swivels’ it pulls one microtubule past the
next, causing the cilium to bend
...
They are bacteria and are much smaller than Eukaryotic
cells
...

• ATP production takes place in specialised infolded regions of the cell surface membrane
• Some have Flagella

Plant cells have a cell wall
...
This is kept rigid by the
pressure of the fluid inside the cell, so supports the cell and therefore the entire plant
...
This maintains the cell stability by making the cell turgid as it increases the
pressure inside the cell
...

Nucleus - Larges organelle
...
RER is
studded with ribosomes, SER is not
...
Some are in the cytoplasm and some are bound to the RER
Mitochondria - Spherical or sausage shaped
...

Lysosomes - Spherical sacs
...

Chloroplasts - Only in plant cells
...
Contain Thylakoids
...
Pair of them next to Nucleus in Animal cells
...


(a) How hydrogen bonding occurs between water molecules, and relate this, and other
properties of water, to the roles of water for living organisms
A range of roles that relate to the properties of water, including solvent, transport medium,
coolant and as a habitat AND roles illustrated using examples of prokaryotes and
eukaryotes
...
This is because the oxygen atom pulls the shared electrons towards it, meaning
that water is slightly negatively charged and the oxygen are positively charged at the hydrogen ends, so
they can form hydrogen bonds with each other
...

Property of water
Solvent

Importance
Metabolic processes in all
organisms rely on
chemicals being able to
react together in solution
...


Examples
70-95% of cytoplasm is
water
...

Cohesion also makes long,
thin water columns very
strong and difficult to
break
...
Ice is less
dense than water so it
floats which insulates the
water and prevents it
freezing completely
...

Large bodies of water
have fairly constant
temperatures
...
Water
has high specific heat
capacity, which means
that a lot of energy is
needed to warm it up
...


Transport of water in the
xylem relies on water
molecules sticking to each
other as they are pulled up
the xylem in the
transpiration stream
Some small organisms
make use of surface
tension to ‘walk on water’
Organisms such as polar
bears live in an
environment of floating ice
packs
...

Many land-based
organisms use evaporation
as a cooling mechanism,
for example in panting or
sweating

Hydrogen bonds
If the solute is slightly
charged or ionic, they will
interact with water
molecules
...

This is because hydrogen
bonds pull the water in at
the surface
...
As
water cools, its density
increases until the
temperature drops to 4˚C,
the density increases
again, so ice floats on
water
...

The evaporation of water
uses a relatively large
amount of energy, so
water evaporating from
the surface ‘removes’ heat
energy from the surface

Metabolic

Water takes part as a
reactant in some chemical
processes

Evapouration

A lot of energy is needed
to cause evaporation,
which is used to cool the
surfaces of living things
...
Water has high
latent heat capacity
...

Explain the difference between specific heat capacity and latent heat capacity (b) what role
does each play in the survival of living things?
(b) The concept of monomers and polymers and the importance of condensation and
hydrolysis reactions in a range of biological molecules
Concept of monomers and polymers:
Polymers – long chains of repeated units
...

Monomers – are one of the smaller similar molecules that join together to form a polymer
...


Many molecules are polymers
...
There are 3 biologically important groups of polymers found in
living organisms: nucleic acids, polysaccharides and proteins
...
They are made up of:
1) Five-carbon or pentose sugar
...

2) Phosphate group
3) Nucleotide base
...
The nucleotides that make up
DNA contain one of the bases A,C,G or T
...

Complex carbohydrates such as starch and cellulose are polysaccharides – a group of polymers
make up of monosaccharides
...
There are 20 different amino acids used to build
proteins
...

Type of molecule
Carbohydrates (C,O,H)
Proteins (C,O,H,N,S)
Nucleic acids (C,O,H,N,P)

Monomer
Monosaccharides (e
...
glucose)
Amino acids
Nucleotides

Condensation, hydrolysis &polymerisation :

Polymer
Polysaccharides (e
...
starch)
Polypeptides & proteins
DNA & RNA




Condensation – a reaction that releases a molecule of water
Hydrolysis – splitting a large molecule into 2 smaller molecules by the addition of water

A condensation reaction occurs when 2 molecules are joined together with the removal of water
...
The bond can be broken again by adding a water molecule – this is called
hydrolysis
...
The reaction involves the breaking & formation of covalent bonds
...
They are soluble & sweet reducing sugars
...
g
...

Hexose sugars – hexose monosaccharides contain 6 carbons e
...
glucose
...
The structures of a-glucose & b-glucose are shown
below
...
This difference has a large effect on the way they bond
together and the polysaccharides produced
...


Disaccharides are 2 monosaccharides bonded together
...
Disaccharides are soluble & sweet
...

Disaccharide formation – formed by a condensation reaction between 2 monosaccharides
...
This forms a 1,
4 glycosidic bond & releases water
...
This means that the remaining O joins to the C on the other glucose,
making a disaccharide
...
The –H
returns to the O and the –OH returns to the C4
...
Starch is actually a combination of 2 molecules,
amylose & amylopectin
...
The subunits are joined by 1, 4
glycosidic bonds
...
The hydroxyl group on carbon 2 of each subunit is
hidden inside the coil
...

Amylose is used for the storage of glucose subunits & energy in plant cells
...
It is insoluble, which means the molecules do not affect the water
potential of the cells
...
They can be used as building
blocks to build other substances or as a substrate in respiration to release stored energy
...
Some of the glucose subunits also have 1, 6 glycosidic
bonds as well as the 1, 4 glycosidic bonds
...

Amylopectin occurs in plants & has a few branches
...
Glycogen has more 1, 6 glycosidic bonds, making it more branched
...
It has the same
advantages as amylose; it’s insoluble and compact
...
The subunits are joined by a 1, 4
glycosidic bond
...

The hydroxyl groups on carbon 2 of each subunit are exposed, allowing hydrogen bonds to form
between adjacent cellulose molecules
...

Cellulose is strong & completely insoluble
...


Amylose
 Made up of a-glucose
 Straight chain
 Tends to coil up
 Plant storage polysaccharide

Cellulose
 Made up of b-glucose (in a chain,
alternate glucose subunits are inverted)
 Forms straight chains
 The b-glycosidic bond can only be
broken down by a cellulose enzyme,
which herbivores have, but humans do
not
 Forms plant cell walls

Glucose + fructose  sucrose
Glucose +glucose  maltose
Glucose +galactose  lactose
Disaccharides can be converted back to monosaccharides by hydrolysis
...

Explain why cellulose is insoluble
...


Insoluble in water so
does not affect the
water potential of the
cell

Because it is so
highly branched it
can be broken
down to glucose
very quickly

Hundreds of the polypeptide chains lie
side by side forming hydrogen bonds
with each other- very strong
...
The elimination of 1 water
molecule is shown
...


Phospholipid - Glycerol plus two fatty acids and a phosphate group
A phospholipid is a molecule containing 1 glycerol molecule, a phosphate group and two fatty acid
chains
...


Phospholipids are similar to triglycerides, but 1 of the fatty acid chains is replaced by a phosphate
group
...

The phosphate group is complex and includes choline, which is water soluble
...
This group makes the ‘head’ end of the phospholipid able to mix
with water – it is hydrophilic
...

This is the basis of all cell membranes
...
They include
triglycerides, phospholipids, glycolipids and cholesterol
...

Lipids
They contain large amounts of carbon and hydrogen & smaller amounts of oxygen
...

3 most important lipids in living things: triglycerides, phospholipids and steroids
...
They are examples of
macromolecules
...
It is an alcohol, which means it has free –OH groups
...




Glycerol, a 3-carbon molecule with 3 OH groups

Fatty acids
Have a carboxyl group (-COOH) on one end, attached to a hydrocarbon tail, made of only carbon &
hydrogen atoms
...
The carboxyl group ionises into H+
and a –COO- group
...







If a fatty acid is saturated (above image) this means that there are no C=C bonds in the
molecule
...

A single C=C bond makes fatty acid monounsaturated
...
g
...
More than one C=C
bond makes it polyunsaturated e
...
linoleic acid
...
Because these kinds push the molecules apart slightly, it makes
them more fluid
...
If there are more unsaturated fatty acids, melting point is lower
...
A condensation reaction
happens between the –COOH group of the fatty acid & the –OH group of the glycerol
...
Because it’s a condensation
reaction, a water molecule is produced, and the covalent bond formed is known as an ester bond
...

The formation of a triglyceride (shown below)
...

Triglyceride
 Compact energy store
 Insoluble in water
 Does not affect cell
water potential

Phospholipid
 Part hydrophilic, part
hydrophobic, so ideal
basis for cell surface
membranes

Cholesterol
 Small, thin molecules
that can fit into the
lipid bilayer giving
strength & stability
...

The first step is to hydrolyse the ester bonds, & then both glycerol & the fatty acids can be broken
down completely to carbon dioxide & water
...
Mammals store fat in adipose cells under the skin
...
This is because lipids have a higher portion of hydrogen
atoms than carbohydrates, and almost no oxygen atoms
...
Lipid in
nerve cells act as an electrical insulator
...

Buoyancy – because fat is less dense than water, it is used by aquatic mammals to help them stay
afloat
...
The peptidoglycan cell wall of some bacteria is covered in a lipid-rich outer coat
...
There are 20 different amino acids used in
proteins, but all have the same basic structure
...
Each amino acid contains elements carbon, hydrogen, oxygen &
nitrogen
...

All proteins consist of long, unbranched chains of amino acids, which are held together by peptide
bonds
...
A peptide bond is formed by condensation
...

2 amino acids together make a dipeptide
...


A peptide bond is the bond between 2 amino acids
...

A dipeptide is formed when 2 amino acids are joined together by a peptide bond
...


(l) The synthesis and breakdown of dipeptides and polypeptides, by the formation and
breakage of peptide bonds
Amino acids are joined together by covalent bonds called peptide bonds
...
Enzymes catalyse these reactions
...
They also break down protein hormones so that
their effects are not permanent
...
2 amino
acids are joined together (dipeptide)
...
A protein may consist of a single polypeptide chain or more than 1 chain bonded
together
...

Primary structure - The sequence of amino acids found in a protein molecule
...

Secondary structure (with reference to hydrogen bonding) – this is formed when the chain of amino
acids becomes folded/coiled
...

Tertiary structure (with reference to hydrophobic and hydrophilic interactions, disulfide bonds and
ionic interactions) – this is formed when the coiled & pleated chains can be folded further to
produce the final three-dimensional shape of the molecule
...
These bonds include:




hydrogen bonds between polar R groups
ionic bonds between R groups with opposite chargers
Covalent disulfide bonds between two sulphur-containing R groups
...
Others are hydrophilic & twist outwards so that they are on the outside of the molecule
...
However, some proteins consist of more than one
polypeptide chain – e
...
haemoglobin has 4 polypeptide chains & collagen has 3
...


(n) The structure and function of globular proteins including conjugated protein
To include haemoglobin as an example of a conjugated protein (globular protein with a prosthetic
group), a named enzyme and insulin
A conjugated protein is a globular protein with a prosthetic group
...
These proteins are
more water soluble
...
Their shape & activity are sensitive to temperature changes: higher temperatures can cause
distortion of their shape
...
Each of these has its own tertiary structure, but when fitted together they form one
haemoglobin molecule
...
The interactions between the polypeptides give the molecule a very specific shape
...
Groups
like this are called prosthetic groups
...
The haem group contains an iron ion
...


The function of haemoglobin is to carry oxygen from the lungs to the tissues in the form of
oxyhaemoglobin
...
When it binds, haemoglobin turns from a purple red colour to bright red
...
One oxygen molecule can
attach to each haem group, so a haemoglobin molecule can carry four oxygen molecules
...
They
tend to form fibres that have structural functions and examples include collagen, keratin & elastin
...
It is not easily stretched
...
It is found in tendons, which
hold muscle to bone, and in bone, where it is hardened by calcium phosphate
...
It is strong & is used for protecting delicate parts of
the body
...
The cells in
the outer layer of skin also contain keratin, which makes them impermeable to water
...
Tropoelastin is coiled like a spring &
can stretch & recoil
...

(p) The key inorganic ions that are involved in biological processes
To include the correct chemical symbols for the following cations and anions: Cations  calcium
ions (Ca2+), sodium ions (Na+), potassium ions (k+), hydrogen ions (H+), ammonium ions (NH4+)
...


PAGE 32 IN NOTES BIOLOGY BOOK! PAGE
72 IN BIOLOGY TEXTBOOK!

(q)






How to carry out and interpret the results of the following chemical tests :
Biuret test for proteins
Benedict’s test for reducing and non-reducing sugars
Reagent test strips for reducing sugars
Iodine test for starch
Emulsion test for lipids

Molecule tested for

Test name

Details of test

Positive result

Protein

Biuret test

Dissolve in water
...


Colour change from
blue to purple
...
g
...

Colour change from
blue to brick red
...
g
...
Add
benedict’s reagent
...

Test the substance for
reducing sugars to
ensure that none are
present, and then
dissolve in water
...

Neutralise the solution
by adding a few drops
of dilute sodium
hydroxide
...

Dissolve in water
...


Lipids

Emulsion test

Dissolve in alcohol
...
Add water to the
filtrate
...


Colour changed from
yellow to deep
blue/black if starch is
present
...


(r) Quantitative methods to determine the concentration of a chemical substance in a
solution
When testing for reducing sugars such as glucose, the colour change may not be complete: the
colour may show a change from blue to green or yellow before going orange or red
...
This
is what causes an incomplete colour change
...
e
...
Create a range of colours using
known concentrations of reducing sugars to create a set of colour standards
...
This will deposit the colour precipitate at the bottom of the tube,
leaving a blue solution of unused Benedict’s reagent
...
The intensity of the blue colour in the solution can be measured using a
colorimeter
...
Use your
graph to determine the concentration of the unknown solution reading from the absorbance
measurement across the concentration
...

A solution with low concentration of glucose contains less glucose than one with high concentration
...
If there is a lot of glucose present, it will
react with more of the Benedict’s reagent, leaving less or none remaining
...
There are 2 key components, known as the stationary phase & the mobile phase
...
The paper is
made of cellulose
...
In each case, there are free –OH groups pointing outwards, in contact with the
mobile phase
...
At a simple level, we can use water (for polar
molecules) or ethanol (for non-polar molecules)
...


(ii) Practical investigations to analyse biological solutions using paper or thin layer
chromatography

PAGE 78-79 IN TEXTBOOK

(a) The structure of a nucleotide as the monomer from which nucleic acids are made
To include the difference between RNA and DNA nucleotides, the identification of the purines and
pyrimidines, the type of pentose sugar
...
They are
phosphate esters of pentose sugars, where a nitrogenous base is linked to the C1 (carbon 1 atom) of
the sugar residue, & a phosphate group is linked to either the c5 or c3 of the sugar residue, by
covalent bonds formed by condensation reactions
...
A nucleotide has 3 components:




A phosphate group
A pentose sugar
An organic base

Feature
Pentose sugar
Purines (2 rings)
Pyrimidines (1 ring)

RNA
Ribose
Adenine & guanine
Cytosine & uracil

DNA
Deoxyribose
Adenine & guanine
Thymine & cytosine

The structure of RNA
RNA is a polynucleotide
...
The sugar involved is
ribose, not deoxyribose
...
There are three
types of RNA:




MRNA – which carries the code held in the genes to the ribosomes where the code is used to
manufacture proteins
TRNA- which transport amino acids to the ribosomes
RNA – which makes up the ribosome

The structure of DNA
DNA is also a polynucleotide
...
They
pair according to their complementary shapes
...
The 2 polynucleotide strands lie in opposite directions, which are known an
antiparallel
...
The
whole molecule twists to form a helix, hence the name ‘double helix’
...
This is why A cannot bind to C & T
and why T cannot bind to G
...
The bonds are formed by
condensation & are called phosphodiester bonds
...
These bonds
form between the sugar of 1 nucleotide & the other phosphate group of another, making a sugarphosphate ‘backbone’
...


(c) The structure of ADP and ATP as phosphorylated nucleotides
...

ADP and ATP are phosphorylated nucleotides
...


Structure of ATP:

d) (i) the structure of DNA (deoxyribonucleic acid)

Structure of ADP:

(d) (ii) practical investigation into the purification of DNA by precipitation
To include how hydrogen bonding between complementary base pairs (A to T, G to C) on two
antiparallel DNA polynucleotides leads to the formation of a DNA molecule, and how the twisting
of DNA produces it’s ‘double-helix’
...
The hydrogen bonds between the bases are broken apart & the DNA
‘unzips’ to expose the bases
...
DNA polymerade catalyses the formation of covalent bonds between the
phosphate of one molecule & the sugar of the next
...
These are ‘proof-read’ by DNA polymerase to prevent mistakes
...

The genetic code is near universal, because in almost all living organisms the same triplet of DNA
bases codes for the same amino acids
...

The genetic code is described as degenerate, because, for all amino acids, except methionine &
tryptophan, there is more than 1 base triplet
...

The genetic code is also non-overlapping, as it is read starting from a fixed point in groups of 3 bases
...

(g) Transcription and translation of genes resulting in the synthesis of polypeptides
To include, the roles of RNA polymerase, messenger MRNA, TRNA, RNA
...
2) translation – converting the code to a sequence of amino acids
...
This is a copy of the DNA coding
strand
The mRNA peels away from the DNA and leaves the nucleus from the nuclear pore
The mRNA attaches to a ribosome




Then tRNA molecules bring amino acids to the ribosome in the correct order, according to
the base sequence on the mRNA
The amino acids are joined together by peptide bonds to give a protein with a specific
tertiary structure

Transcription and translation
-

-

A gene unwinds & unzips
...
A bonds with T; C
with G; G with C; and U with A, on one strand of the unwound DNA
...

The length of RNA that is complementary to the template strand of the gene is produced
...

The mRNA now 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 nuclear envelope, and then come together to form he ribosome
...
Ribosomes are made of ribosomal RNA &
protein in roughly equal parts
...

They are single-stranded polynucleotides, but can twist into a hairpin shape
...
At the loop of the hairpin is
another triplet of bases, called an anticodon that is complimentary to a specific codon (triplet) of
bases on the mRNA
...
Different versions of a
particular gene are called alleles
...
Mutations are random
and spontaneous
...
Some can be advantageous – a white coat in an animal during winter when snow is on
the ground
...


(a) The role of enzymes in catalysing reactions that affect metabolism at a cellular and whole
organism level

Enzymes are called globular biological catalysts because they speed up metabolic reactions in living
organisms
...





Catalysts speed up chemical reactions & remain unchanged at the end of the reaction, able
to be used again
A small amount of catalyst can catalyse the conversion of a large number of substrate
molecules into product molecules
The number of reactions that an enzyme molecule can catalyse per second is known as its
turnover number

(b) The role of enzymes in catalysing both intracellular and extracellular reactions
To include catalase as an example of an enzyme that catalyses intracellular reactions and amylase
and trypsin as examples of enzymes that catalyse extracellular reactions
...
Alternatively, enzymes may be extracellular (working outside cells),
such as the digestive enzymes amylase and trypsin, which are released into the digestive system
...

Specificity,
The active site of an enzyme is a specific shape, depending on the reaction that it catalyses, meaning
that other molecules won’t fit into the active site
Active site:
The area on an enzyme to which the substrate binds
Lock and key hypothesis:
The theory of enzyme action in which the enzyme active site is complementary to the substrate
molecule, like a lock and key
Induced-fit hypothesis:
The theory of enzyme action in which the enzyme molecule changes shape to fit the substrate
molecule more closely as it binds to it
Enzyme-substrate complex:
The intermediary formed when a substrate molecule binds to an enzyme molecule
Enzyme-product complex:

The intermediate structure in which product molecules are bound to an enzyme molecule
Lowering of activation energy:
Enzymes reduce the activation enthalpy so the reaction can proceed at a much lower temperature

(d) (i) The effects of pH, temperature, enzyme concentration and substrate concentration on
enzyme activity

pH:
-

Low pH = lots of H+ ions
H+ ions have a positive charge
Either extreme of H+ ion concentration can interfere with the hydrogen and ionic bonds
holding the tertiary structure together
...

But heat also makes the molecules vibrate
...

In enzymes there are large numbers of these bonds holding the tertiary structure, and
especially the active site, in place
...
At higher concentrations, all of the active sites become filled, so the rate of
reaction remains the same

(d) (ii) practical investigations into the effects of pH, temperature, enzyme concentration and
substrate concentration on enzyme activity
pH:
A starch-agar plate is made up by mixing starch with agar
...
It forms a semi-rigid gel in the plate
...
Into
each well place the same volume of a different pH buffer solution
...
Into the well without the amylase, add an equal
volume of distilled water as a control
...
Flood the plate with an
iodine solution and rise with water
...
Place an equal number of discs in each of seven tissues and place one in each of a range of
water baths from 20-80˚C
...
Allow to equilibrate
...

Close the clip
...
Time how long it takes for the bubble to move 5cm
...

(e) The need for coenzymes, cofactors and prosthetic groups in some enzyme-controlled
reactions
To include Cl – as a cofactor for amylase, Zn2+ as a prosthetic group for carbonic anhydrase and
vitamins as a source of coenzymes
...
Their presence allows enzyme
substrate complexes to form more easily
...
They may bind just before, or at the same time, as the substrate binds
...
Unlike the
substrate, coenzymes are recycled back to take part in the reaction again
...
Some coenzymes are permanent parts of the enzymesprosthetic groups
...

(f) The effects of inhibitors on the rate of enzyme controlled reactions
To include competitive and non-competitive and reversible and non-reversible inhibitors with
reference to the action of metabolic poisons and some medicinal drugs, and the role of product
inhibition
Competitive inhibitor molecules:
Have a similar shape to that of the substrate molecule
...
These complexes do not lead to the formation of products
because the inhibitor is not identical to the substrate
...
Where the number of substrate molecules is increased,
the level of inhibition decreases because a substrate molecule is more likely than an inhibitor
molecule to collide with the active site
...
They bind for a short period of time and then leave
...

Non-competitive inhibitors:
Do not compete with substrate molecules for a place in the active site
...
The attachment of non-competitive
inhibitors distorts the tertiary structure of the enzyme molecule, leading to the shape of the active
site changing
...
The level of inhibition depends on
the number of inhibitor molecules present
...
Changing the
substrate concentration will have no effect on this form of inhibition
...
The inhibition is irreversible, and any enzyme
molecule bound by inhibitor molecules are effectively denatured
...

Cells and partially permeable barriers

Because cell membranes form a barrier and separate the cell contents from the cell’s exterior
environment, or separate organelles from cytoplasm, they need to allow some molecules through,
into or out of the cell
...

Permeability refers to the ability to let substances pass through
...
The properties of the component molecules of the cell membrane
determine is permeability – i
...
which molecule it allows through
...

Regulates transport of materials into & out the cell
May contain enzymes involved in specific metabolic pathways
Has antigens, so that the organism’s immune system can recognise the cell as being ‘self’
and not attack it
May release chemicals that signal to other cells
Contains receptors for such chemical signals, and so is a site for cell communication or
signalling, hormones & drugs may bind to membrane-bound receptors
May be the site of chemical reactions

Within cells
The membranes around many organelles present in the eukaryotic cells separate the organelle
contents from the cell cytoplasm, so that each organelle is a discrete entity and able to perform its
function
...






Mitochondria have folded inner membranes called cristae
...

The inner membranes of chloroplasts, called thylakoid membranes, house chlorophyll
...

There are some digestive enzymes on the plasma membrane of epithelial cells that line the
small intestine, and these catalyse some of the final stages in the breakdown of certain types
of sugars
...
A fluid
mosaic model consists of:







A bilayer of phospholipid molecules
Cholesterol which regulates the fluidity of the membrane, making it more stable
Glycolipids & glycoproteins that function in cell signalling or cell attachment
Protein molecules that float in the phospholipid bilayer
...
Others are embedded in
the membrane – these are called intrinsic proteins
...

The fluid mosaic model is the accepted structure of membranes in a cell

Phospholipids
Phospholipids form a barrier that limits movement of some substances into and out of the cell, or
into and out of the organelles, so the membrane is partially permeable
...
Water-soluble molecules
and ions cannot easily dissolve and cross the membrane
...

Cholesterol
Cholesterol fits between the tails of the phospholipid molecules
...
It also holds the phospholipid tails together,
for mechanical stability
...

Glycolipids and glycoproteins
The carbonate group on the protein or lipid molecules always has a specific shape and is used to
recognise the cell – to identify it as ‘self’ or ‘foreign’
...

Drugs and hormones can bind to these membrane-bound receptors
...
For example, asthmatics take salbutamol, which fits the receptors on
smooth muscle in the airways to cause relaxation
...
The
shape of the glycoprotein or glycolipid may be complementary to the shape of a signalling molecule
in the body
...
g
...
If the correct
binding site is not present, the cell cannot respond to the signalling molecule
...

Proteins

Proteins have a variety of functions, such as enzymatic activity and cell signalling
...
For example, some proteins may form:



Pores that allow the movement of molecules that cannot dissolve in the phospholipid bilayer
Carrier molecules that allow facilitated diffusion active pumps

(c) (i) factors affecting membrane structure and permeability
To include the effects of temperature and solvents
Increasing the temperature means that the molecules have more kinetic energy
...

Temperature

Membranes are partially permeable, fluid and stable at normal body temperature
...
This increases the permeability
of the membranes to certain molecules
...
This is because as the phospholipids move about, they leave temporary
gaps between them, providing space for small molecules to enter the membrane
...
Eventually, the proteins in the membrane
will denature
...

Solvents
Solvents such as alcohol dissolve fatty substances
...

(d) (i) the movement of molecules across membranes
To include diffusion and facilitated diffusion as passive methods AND active transport, endocytosis
and exocytosis as processes requiring ATP as an immediate source of energy
...
Cells therefore need to receive raw material or
reactants for these reactions
...
Therefore, they need oxygen and glucose
...
Some
substances can pass across cell membranes without using any of the cell’s metabolic energy
...

Passive transport (diffusion and facilitated diffusion including the role of membrane proteins):
Passive transport is the transport of a molecule without using energy
...

Large and charged molecules need to be transported across the phospholipid bilayer, they can’t just
diffuse across
...

Active transport: The movement of molecules or ions across membranes, using ATP to drive ‘protein
pumps’ within the membrane
Endocytosis: When large quantities of a material are brought into the cell
...

Exocytosis: When large quantities of a material are moved out of the cell
...

(e) (i) the movement of water across membranes by osmosis and the effects that solutions of
different water potential can have on plant and animal cells

Osmosis can be explain in terms of a water potential gradient across a partially-permeable
membrane
Water potential – is the measure of the concentration of free water molecules
...
As solutes (sugars/salts) are added to a solution, the water
potential gets lower
...
e
...

Water molecules will move from a solution with a higher water potential to a solution with a lower
(more negative) water potential
...

Osmosis
Osmosis is the movement of water molecules from a region of higher water potential to a region of
lower water potential across a partially permeable membrane
...

There is a water potential gradient from high outside the cell to lower inside the cell
...

A cell placed in a strong salt solution has higher (less negative) water potential than the surrounding
solution
...

(eii) practical investigations into the effects of solutions of different water potential on plant and
animal cells
The effects of osmosis on animal and plant cells:
Solution
Cell type
Animal

Pure water
An animal cell has no cell wall
...

The vacuole is full of watery sap
and the cytoplasm pushes the
plasma membrane out against
the cell wall
...


(ii)

Strong salt
An animal cell has no cell wall
...
Its
appearance is known as
crenelated
...

It will become flaccid
...
The
cytoplasm will also shrink and
the plasma membrane pulls
away from the cell wall
...


Practical investigations into factors affecting membrane structure and permeability

The effect of temperature on beetroot cell membranes
1) Wear eye protection
2) Inside beetroot cells, within the large vacuole that is bound by a tonoplast membrane, are
nitrogenous, water-soluble pigments called betacyanins, a type of betalain
...

4) The amount of leakage of the red pigment is proportional to the degree of damage to the
beetroot plasma and tonoplast membranes, and can be measured using a colorimeter, but
measuring the absorbance of green light (Wavelength range 530-550 nm)
Effect of solvents on phospholipids
Organic solvents such as acetone & ethanol will damage cell membranes as they dissolve lipids
...
The molecules
vibrate as they acquire more kinetic energy, breaking the hydrogen bonds
...
Vibration of the protein molecules
does not break the peptide bonds between the amino acids
...
Mitosis
is a small part of the cycle
...
During interphase, the cell also increases in
size, produces new organelles & stores energy for another division
...






S phase (synthesis); DNA replicates, when all chromosomes have been duplicated, each one
consists of a pair of identical sister chromatids
...
Cytokinesis (cytoplasmic division)

Explain why the cell must copy the DNA before mitosis
Explain why the cell must produce new organelles and store energy during interphase
(c) The main stages of mitosis
(d) Sections of plant tissue showing the cell cycle and stages of mitosis
(e) The significance of mitosis in life cycles
To include the changes in the nuclear envelope, chromosomes, chromatids, centromere,
centrioles, spindle fibres and cell membrane
To include the examination of stained sections and squashes of plant tissue and the production of
labelled diagrams to show the stages observed
To include growth, tissue repair and asexual reproduction in plants, animals and fungi
...

3) Replacement of old cells
4) Asexual reproduction: single-celled protoctists such as Amoeba and Paramecium divide by
mitosis to produce new individuals
...
g
...
Fungi, such as single-celled yeasts,
can produce asexually by mitosis
...
Aphids may sometimes produce eggs, by mitosis, that
doesn’t not need fertilising
...
Cells grow during interphase and mitosis repairs
tissues, not cells
...

- In animal cells, the plasma membrane folds inwards and ‘nips in’ the cytoplasm
...

Two new daughter cells are now formed
...

INVESTIGATION - making a root-tip squash to examine cells in stages of mitosis
Once plant cells have divided and differentiated and have a vacuole and rigid cellulose cell
wall, they cannot divide
...
Cells of root tips can be stained with acetic orcein (which stains chromosomes) and
observed under a microscope, to see the stages of mitosis
...
Members of a homologous pair of chromosomes pair up
during meiosis
...

In your body cells there are 46 chromosomes
...
These can form matching pairs – 1 material
and 1 paternal chromosome containing the same genes at the same places on the
chromosome
...
Although they
have the same genes, they may contain different alleles (variants) for the genes
...

Genetic variation within a population increases it chances of survival when the environment
changes, as some individuals will have characteristics that enable them to be better adapted
to the change
...
For sexual reproduction to
occur, they must produce haploid gametes, so zygote is produced and the normal
chromosome number is maintained through the generations
...

The diploid cells undergoing meiosis are in specialised organs called gonads – ovaries and
testes
...

Meiosis is an alternative form of cell division
...
These
cells contain 1 chromosome from each pair of homologous chromosomes
...
In meiosis,
the chromosomes pair up in their homologous pairs
...

- In the first meiotic division, the four stages are: prophase 1, metaphase 1, anaphase 1 and
Telophase 1
...
This
takes place in a plane at right angles to that of meiosis 1
...


How meiosis produces genetic variation






Crossing over during prophase 1 shuffles alleles (not an example of mutation)
Independent assortment of chromosomes in anaphase 1 leads to random
distribution of maternal and paternal chromosomes of each pair
Independent assortment of chromatids in anaphase 2 leads to further random
distribution of genetic material
Haploid gametes are produced, which can undergo random fusion with gametes
derived from another organism of the same species
...

Erythrocytes and neutrophils both originate as undifferentiated stem cells in bone marrow
...
They are filled with haemoglobin, the shape of the cell changes to
become a biconcave disc so that it is capable of transporting oxygen from the lungs to tissues
...
The lysosomes contain enzymes so that the
neutrophil can ingest invading microorganisms
...

In xylem, the meristem cells elongate and the walls become elongated and waterproofed by
deposits of lignin, which kills the cell contents
...
They are suited to transporting water and minerals up the plant,
and also support the plant
...
Next to each sieve plate is a companion cell which is very
metabolically active and used in moving the products of photosynthesis up and down the plant
...

Erythrocytes (red blood cells) carry oxygen in the blood:





Biconcave disc shape ( to provide a large surface area to take up oxygen quickly)
No nucleus = more room for haemoglobin (to bind to the oxygen)
Small and flexible (to fit through tiny capillaries)

Neutrophils (engulf and digest foreign matter or old cells):









Flexible shape (to enable movement through tissues)
Lobed nucleus (to help movement through membranes)
Many ribosomes (to manufacture digestive enzymes)
Many lysosomes ( to hold digestive enzymes and to break down the engulfed particles)

Many mitochondria (to release the energy needed for activity)
Well-developed cytoskeleton (to enable movement)
Membrane-bound receptors (to recognise materials that need to be destroyed

Epithelial cells (act as surfaces):








May be ciliated (to move mucus)
May be cuboid (to provide a barrier)
Often squamous ( to cover a large area)
Often tin (to provide short diffusion distance)
Some have microvilli to increase surface area
Many glycolipids and glycoproteins in cell-surface membrane (to hold cells together or for
cell signalling)

Sperm cells (carry the paternal chromosomes to the egg):




Many mitochondria (to release the energy needed for rapid movement)
Specialised lysosome in sperm head which contains an enzyme specialised to break down
the egg wall





Flagellum (to enable rapid movement)



Root hair cells (absorb water and mineral ions from the soil):



Root hair cells are epidermal cells on the outer layer of young plant roots



The hair-like projection greatly increases the surface area for absorption of water and
mineral ions, such as nitrates, from the soil into which it projects



Mineral ions are actively transported into the root hair cells, lowering the water potential
within them, causing water to follow by osmosis, down the water-potential gradient
...

These cells will also produce ATP, as this is needed for active transport
...
However, they cannot carry out photosynthesis, as they do not have the enzymes
needed for the second stage of the process:













Light energy is used to produce ATP
The ATP actively transports potassium ions from surrounding epidermal cells into the guard
cells, lowering their water potential
...

The guard cells swell, but at the tips the cellulose cell wall is more flexible, and it is more
rigid where it is thicker
...

As these stomata open, air can enter the spaces within the layer of cells beneath the
palisade cells
...
As they
use it for photosynthesis, this will then maintain a steep concentration gradient
...

When the stomata are open, water vapour also exists from them
...
In light they absorb water to become turgid and allow
exchange of gases
...

They may be similar to each other or they may perform slightly different roles
...


-

Xylem contains vessels that carry water and xylem fibres for support
Phloem contains two types of cell – sieve tube elements which form sieve tubes, and
companion cells
...

The cooperation between cells, tissues, organs and organ systems
Movement: the muscular & skeletal system must work together for movement to
take place, but this can only happen if the nervous system ‘instructs’ muscles to coordinate
their actions
...
They use energy, so they require a supply of
nutrients and oxygen from the circulatory system, which in turn receives the chemicals from
the digestive and ventilation systems
...
They maintain the capacity to
undergo mitosis and differentiate into a range of cell types
...

Stem cells are renewing source of undifferentiated cells for the growth and repair of tissues
and organs
...
Stem cells have the ability to use all
their genes
...

-

-

Ciliated epithelia: column shaped, exposed surface covered with cilia, moved in
synchronised waves, found on surface of tubes (e
...
bronchi, oviduct), waft mucus in
lungs, egg in oviduct
Xylem: composed of xylem vessel cells and parenchyma cells, parenchyma cells fill
the gaps between xylem vessels to provide support
Phloem: comprises of sieve tubes and companion cells, companion cells are highly
metabolically active, moving products of photosynthesis up and down the phloem
Squamous epithelial tissue: Flattened cells that form a thin, smooth, flat surface
...


(k) The production of erythrocytes and neutrophils derived from stem cells in bone
marrow
The production of blood cells
Stem cells in the blood marrow divide and differentiate to form both red and white
blood cells
...
They have no
nucleus and very few organelles, providing more space for haemoglobin molecules which
are synthesised during development before the other organelles are lost
...

(l) The production of xylem vessels and phloem sieve tubes from meristems
The production of xylem vessels and phloem sieve tubes

Xylem and phloem are transport tissues in plants
...
These cells are expanded by the uptake of water and the development of a
vacuole
...

Xylem
Lignin is deposited in their cell walls to strengthen and waterproof the wall
...
These form tubes with wife lumens to carry water and dissolved minerals
...

Phloem
Phloem consists of two types of cell that work together:
1) Sieve tube elements lose their nucleus and most of their organelles
...

2) Companion cells retain their organelles and can carry out metabolism to obtain
and use ATP to actively load sugars into the sieve tubes
...

Plasmodesmata are connections between cells where the cytoplasm is continuous
...

Stem cells can be sourced from different tissues:
1)
2)
3)
4)

Embryonic stem cells, which are present in a young embryo
Blood from the umbilical cord
Adult stem cells found in developed tissues such as bone marrow
Scientists can also induce certain tissue cells to become stem cells

Stem cells can be used in the following ways in research and medicine
Repair of damaged tissues
Stem cells have been used to treat certain conditions and continued research suggests that
many uses can be found:
1)
2)
3)
4)

Stem cells in bone marrow are used to treat diseases of the blood, such as leukaemia
Stem cells have been used to repair the spinal cord of rats
Stem cells have been used to treat mice with type 1 diabetes
Stem cells in the retina can be made to produce new light-sensitive cells

5) Stem cells directed to become nerve tissue could be used to treat neurological
conditions such as Alzheimer’s disease and Parkinson’s disease
...

Developmental biology
Scientists use stem cells to gain a better understanding of how multicellular organisms
develop, grow and mature
...




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