Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Cells and Cell Structure

Biology - Unit 2

Organelle

Function

Nucleus

An organelle found in many living cells containing the genetic info
...
It takes place because of the random movement of particles in a gas or in a
solution
...
e
...

Diffusion allows substances to move in and out of a cell
...

Oxygen required for respiration passes through cell membranes by diffusion
...
Muscular Tissue - which contracts to move whatever its attached to
2
...
Epithelial Tissue - which covers some parts of the body e
...
the inside of the gut
Tissues are Organised into Organs

- An organ is a group of different tissues that work together to perform a certain function
- Stomach organ is made up of these tissues:
1
...

3
...

2
...

4
...


Glands (e
...
pancreas and salivary glands) which produce digestive juices
Stomach and Small Intestine - digest food
Liver - produces bile
Small Intestine - absorbs soluble food molecules
Large Intestine - absorbs water from undigested food, leaving faeces

- The process by which cells become specialised for a particular job is called differentiation
- Differentiation occurs during the development of a multicellular organism
- These specialised cells then form tissues, organs and organ systems
Plant Organs
- Plants are made or organs like stems, roots and leaves
- These organs are made of tissues
Example:
1
...
Xylem and Phloem - they transport things like water, mineral ions and sucrose around the
plants
3
...
In order to do this plants use photosynthesis
...


Carbon dioxide + water —- (+ light energy) —-> glucose + oxygen
The cells in algae and the leaves of a plant are full of small green parts called chloroplasts
...


- During photosynthesis light energy is absorbed by the
chlorophyll in the chloroplasts
...

Oxygen is a by- product of photosynthesis - it is released
into the air so we can then breathe it in
...


PHOTOSYNTHESIS
IS NOT AEROBIC
RESPIRATION

The Rate of Photosynthesis may be limited by:

- Shortage of light
- Low temperature
- Shortage of carbon dioxide
Not Enough Light

- Light provides the energy needed for photosynthesis
- As the light level is raised, the rate of photosynthesis increases steadily - but only up to a certain
point

- Beyond that it won’t make any difference because then it’ll either be the temperature or the
CO2 level which is the limiting factor
Too Little Carbon Dioxide

- Carbon Dioxide is needed for photosynthesis
- It will only increase photosynthesis up to a certain point
Temperature

- Usually temperature is the limiting factor because it is too low - the enzymes for photosynthesis
work slow at low temperatures

- If it gets too hot the enzymes will denature
- This happens at 45oC
Artificially Creating the Environment Needed for Plants to Grow
Advantages of Greenhouses

Disadvantages of Greenhouses

Farmers can produce perfect plants all year round and also
produce them quicker

It is expensive to heat and ventilated a greenhouse

Plants have more quality photosynthesis time with artificial
light

It is expensive to keep a light on all day long

More CO2 produced so more production of photosynthesis

Parrafin burners (produce carbon dioxide) produce harmful
gases for the environment

Easier to keep plants free from pests and disease and the
farmer can add fertiliser to the soil so the plant gets all the
mineral ions needed

Glucose
How Plants use Glucose:

1

For Respiration
1) Plants manufacture glucose in their leaves during photosynthesis
2) They use some of this for respiration
3) This releases energy which them to convert the glucose into other useful substances, which
they can use to build new cells and grow
4) To produce some of these new substances, they also need to gather a few minerals from the
soil

2

Making Cell Walls
Glucose is converted into cellulose for making strong cell walls, especially in a rapidly growing plant

3

Making Proteins
Glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are
then made into proteins

4

Stored in Seeds
Glucose is turned into lipids (fats and oils) for storing in seeds
Sunflower seeds, for example, contain a lot of oil
Seeds are also stored as starch

5

Stored as Starch

- Glucose is turned into starch and stored in the roots, stems and leaves, ready for use when
photosynthesis isn't happening - like in the winter

- Starch is insoluble which makes it better for storing than glucose - a cell with lots of glucose in
would draw in loads of water and swell up

Organisms and Their Environment & Distribution of Organisms
Physical Factors that may affect organisms are:
- Temperature
- Availability of nutrients
- Amount of light
- Availability of water
- Availability of oxygen and carbon dioxide
An organism might live on one area over another due to differences in environmental factors
between the two areas
...

There area couple ways to measure and study the distribution of organisms:
- Measure how common an organism is in different sample areas by using a quadrat, and then
comparing them

- Study how the distribution changes across an area e
...
by placing quadrats along a transect
Validity
- For your results to be valid they have to be reliable
- You need to control the variables in order to keep the results valid
- If you control all of the variables that could be affecting the distribution, you'll know whether a
difference in distribution is caused by the environmental factors or not
- Another way to improve the validity is to use random samples e
...
randomly putting down a
quadrant or transect, if all your samples are in the same spot and everywhere else is different
then your results wont be different
Reliability

- To keep them reliable you need to make sure your results are repeatable and reproducible
- You need to use a large sample size, e
...
use as many quadrats and transects as possible in your
-

sample area
Bigger samples are more representable of the whole population - this makes them more
reproducible

Mean - total number of organisms
number of quadrats
Median - middle value when they are lined up in size
Mode - most common value
Sample size is related to both validity and reproducibility

Proteins
- Proteins are made up of long chains of amino acids
- These long chains can be folded into specific shapes so that other molecules can fit into the
protein

- There are 20 different types of amino acids
Proteins act as:- Structural components of tissues such as muscles
- Hormones
- Antibodies
- Catalysts
Catalysts increase the speed of a chemical reaction, it isn't changed or used up in the reaction
...
Protein allows muscle contraction to occur by acting as a structural component
2
...
Proteins allow you to fight illness by creating antibodies with a precise 3D shape
...
Protein makes haemoglobin which allows you to carry oxygen around your body - keeping you
alive
A catalyst (protein enzyme) speeds up the rate of a chemical process’ in the body of an animal or
plant
...


Enzymes
Enzymes are biological catalysts that are made by cells
Enzymes are proteins that are made up from long chains of amino acids
On the surface of enzymes have special indentations called active sites
The shape of the active site specifically ‘fits’ a substrate
Enzymes are specific to one substrate

The enzymes fits into the substrate
exactly

The substrate fits into an active site
Substrate splits into products which leaves the
active site

ENZYME + SUBSTRATE -> ENZYME/SUBSTRATE COMPLEX -> ENZYME + PRODUCT (S)
Temperature and its Effect
- Changing the temperature alters the rate of an enzyme - catalysed reaction
- Higher temperatures increase the rate at first
- If it gets too hot, some of the bonds holding the enzymes together will break, this destroys the
enzymes specific shape and so it won’t work anymore - it is said to have denatured
pH Level and its Effect
- If the pH is too low or too high then it will interfere with the bonds holding the enzymes
together
- This changes the shape and the enzymes denature

- All enzymes have an optimum temperature that the work best at, often this is neutral pH 7, but
not always e
...
pepsin is an enzyme used to break down proteins in the stomach

- It works best at pH 2 - it’s well suited to acidic conditions

Enzymes in Digestion
Digestion -> the break down of large insoluble food molecules to small soluble molecules which
can be absorbed into the blood
...
Mechanical - chewing, churning, biting
2
...
Bile
is released into the small intestine via the bile duct
...

Bile emulsifies the fats
...


Salivary Gland - Produce amylase enzymes in
Saliva
Liver - Bile is produced
...

In the Home:
- Biological detergents may contain protein - digesting and fat - digesting enzymes (proteases and
lipase)
- Biological detergents are more effective at low temperatures than other enzymes
- They are ideal for getting rid of stains like food or blood
In Industry:
- Protease is used to ‘pre-digest’ baby foods
- Carbohydrases are used to convert starch into sugar syrup
- Isomerase is used to convert glucose syrup into fructose syrup, which is much sweeter and
therefore can be used in smaller quantities in slimming foods
- Enzymes are also used to bring about reactions at normal temperatures and pressures that
would otherwise require expensive, energy-demanding equipment
- However they are costly to produce

Advantages

Disadvantages

They're specific so only catalyse (speed up) the
reaction you want them to

Some people can develop allergies to enzymes (e
...

biological washing powders)

Using lower temperatures and pressures means
lower cost as it saves energy

Enzymes can be denatured by a small temperature
increase

Enzymes work for a long time, so after the initial
cost of buying them, they can be used continuingly
without being used up

They are susceptible to poisons and changes in pH this means the conditions they work in must be
tightly controlled

They are biodegradable so cause less environmental They can be expensive to produce
pollution
Contamination of enzymes with other substances
can affect the reaction

Experiments to take notice of:

- Effects of pH and temperature on enzymes (too high and their bonds will break, they'll lose their
shape and denature)

- Testing for breakdown of starch to sugar with amylase using iodine solution
- Testing for the breakdown of proteins to amino acids using egg whites (decrease in mass),
photographic film

- Testing for breakdown of lipids into fatty acids and glycerol by lipase usually measured as a
decrease in pH
Digestive enzymes are described as extra - cellular because they act on the food outside the cells
that produce them

Aerobic Respiration
- Respiration is not the same thing as breathing
- Breathing is more properly called ventilation
- Instead, respiration is a chemical process in which energy is released from food substances, such
as glucose - a sugar

- Aerobic respiration needs oxygen to work
...

Aerobic respiration - Higher Tier
For the higher paper you must recall the symbol equation for aerobic respiration:
C6H12O6 + 6O2 → 6CO2 + 6H2O

- Amino acids are made from combining sugars with nitrate ions and other mineral ions from the
-

soil
...

This process uses energy (glucose) from respiration
...

These may be used in cells as an energy store
...

However glucose is used to build up glucose into more complex carbohydrates like
CELLULOSE
...


Anaerobic Respiration - In Animals
- When you do vigorous exercise your body sometimes can’t supply enough oxygen to your
muscles, they start doing anaerobic respiration instead of aerobic respiration

- Aerobic respiration doesn't require oxygen
- It is the incomplete breakdown of glucose, which produces lactic acid
- This is not the best way to convert glucose to energy because lactic acid builds up inside of the
muscles, which gets painful

- It causes muscle fatigue, the muscles gets tired and stops contracting efficiently
- Anaerobic respiration doesn’t release as much energy as
aerobic respiration

Glucose → Lactic acid (+ Energy Released) <-- HUMAN
This type of respiration may be used when, for example, an animal
is being chased by a predator
...

Oxygen Debt - Higher Tier

- Anaerobic respiration produces an oxygen debt
...
(Get rid of
the lactic acid)
The existence of an oxygen debt explains why we continue to
breathe deeply and quickly for a while after exercise
...


- There were no ‘in-between’ pale lilac flowers
...

• An allele is two different form of a gene
• He had a pea plant with one gene
• This gene had two possible forms called alleles, one was a dominant allele and the other
recessive
...
g
...
g
...
g
...

Genotype means what alleles you'll have
Phenotype means the actual characteristics
Two Homozygous Hamsters:
b = Recessive
B = Dominant

Two Heterozygous Hamsters:
b = Recessive
B = Dominant

Stem Cells
Embryonic Stem Cells are the only ones that an be made to differentiate into any type of cell
...
Umbilical cord blood
2
...
Adult bone marrow

Adult stem cells can develop into a limited number of cells
...

How can Stem Cells be used?

- Stem cells may be able to regrow the nerves which cause paralysis
- Replace Damaged Tissue - may be able to treat a range of conditions in the body e
...
heart
failure, spinal injury, diabetes and Parkinson disease
...

• The cell nucleus contains chromosomes, these chromosomes are made of DNA - along the
length of the chromosomes are genes
...

• We need this special type of cell division because it haves the chromosome number in gametes
so that we have one pair for the child
...

This type of cell division forms gametes
...
This type of cell division forms new cells
...

Replacement tissues:
In Mammels: Under skin, in gut, in
bone marrow
...

Repair of damaged tissues
...
Anthers,
ovules
...


Production of Gametes: Sperm
and Ova
...


Resulting cells are

Genetically Identical

Genetically Different

Number of cell division

1

2

Number of cells at the end
division

2

4

Used in

Asexual Reproduction

Sexual Reproduction

Variation

No (They are clones - genetically
identical)

Yes - they are all different

Female

Male (2n)

Meiosis

Meiosis

Ovum (n)

Sperm (n)

Fertilisation

Zygote (2n)

Mitosis

Embryo

Mitosis
The copies are
joined and next
to each other

Cell Membrane
Cytoplasm
Nucleus
Nucleus before chromosomes
become visible
...


Original and copied
chromosomes separate to move
to opposite ends of the cell

The chromosomes are now visible
...
They are found
in pairs which look the same
...
Two daughter
cells have been formed whose nuclei contain
4 chromosomes genetically identical to the
original 4 of the parent cell

Mitosis

- When a body cell divides by mitosis copies of the genetic material are made, then the cell
divides once to form two identically body cells

- Mitosis occurs during growth or to produce replacement cells
- Body cells have two sets of chromosomes - gametes (sex cells) only have one
Asexual Reproduction and Mitosis

- Some organisms also reproduce by mitosis e
...
strawberry plants form runners in this way,
which can become new plants

- This is an example of asexual reproduction
- The offspring have exactly the same genes as parents - so theres no variation

Meiosis
Meiosis

- Cells in reproductive organs - testes and ovaries in humans - divide to form gametes
- This type of cell division to form gametes is called meiosis
- During sexual reproduction, two cells called gametes (sex cells) combine to form a new
individual

- Gametes only have one copy of each chromosomes, this is so that you can combine one sex
-

cells from the ‘mother’ and one sex cell from the father and still end up with the right number
of chromosomes in body cells
For example, human body cells have 46 chromosomes, the gametes have 23 chromosomes each,
so when and egg and sperm combines, you get 46 chromosomes
The new individual will have a mixture of two sets of chromosomes, cells will divide by meiosis,
it only happens in reproductive organisms

Egg
To make new cells which only have
half original number of chromosomes,
cells divide by meiosis
...
g
...

In the first division in meiosis (there
are two divisions) the chromosomes
pairs line up in the centre of the cell

The pairs are then pulled apart, so
each new cell only has one copy of
each chromosome
...
Its a lot like
mitosis
...


After the two gametes
join at fertilisation meiosis the cells grow
by repeatedly dividing
by mitosis
...


The Difference?
Mitosis

Meiosis

Asexual - only one parent needed

Sexual - two parents needed

Occurs for body cells so they can grow and to
repair and produce replacement cells

Occurs when reproductive cells (testes and
ovaries) divide to form gametes that can be
used in fertilisation

Genetic Variation
There can be different versions of the same gene, for example for different characteristics
The different versions of the same gene are called alleles
Sexual Reproduction gives rise to variation because, when gametes fuse, one pair of each allele
comes from each parent
There are 22 pairs of chromosomes in every human body cell
The 23rd pair of chromosomes carry the genes that determine whether you are male or female
All men have an X and Y Chromosome: XY
The Y Chromosome causes male characteristics
All women have to X Chromosomes: XX
The XX combination allows female characteristics to develop
Each characteristic is controlled by a single gene - each gene may have different forms of alleles
(for example the eye colour gene contains blue eye alleles, brown eye allele etc
...

Each person has different and unique DNA - this can be used to identify individuals in a process
called DNA fingerprinting
...
If the two alleles are the same we say
that the individual is ‘homozygous’ for that gene
...

The dominant allele is always shown in uppercase letters
...

• This removes debris and bacteria
...

Symptoms:
Chest infections
Bacterial infections
Lung damage
Frequent coughing
Wheezing
Shortness of breath
Salty sweat
The thick mucus also blocks the duct between the pancreas and duodenum
This prevents the enzymes passing from the pancreas to the duodenum
Consequently food cannot be digested - tablets have to be taken daily

-

How is Cystic Fibrosis Inherited?
• It is inherited through your genes
• It is caused by chromosome 7
• It is caused by a recessive allele of a gene so the parents can have the gene without knowing
• Sufferers have the genotype aa
• People can be symptomless carriers
• Symptom carries would Aa
• 1 in 20 individuals are carriers
Cystic Fibrosis - c
Not cystic Fibrosis - C

The only way to find out is via genetic testing
...


Dd

A

B

Dd

C

D

E

dd

Dd/DD

dd

G

F
Dd

Dd

H
dd

Embryos can be screened for the alleles that case these and other genetic disorders

Speciation
Why Scientists cannot be certain about how life started on Earth:

- There are various hypothesis but no true evidence to support them
- Lack of evidence - scientists believe the first organisms were soft tissued, soft tissue tends to
decay away completely so fossils cannot be recorded

- There is a lack of valid and reliable results

Speciation is the development of new species:
• A species is a group of organisms that can reproduce and give fertile offspring
• Speciation is the development of new species
• Species occur when populations of the same species become so different that they can no
longer breed together to produce fertile offspring

Old and New Species
Fossils are the remains of an organisms or part of an organism such as bone or shell or the
impression of an organism in rocks from many years ago
...
What the organism looked like
2
...
Generally speaking older fossils are built
into deeper down rocks in the layers
...


Shelled animals
dies and falls to
the bottom of the
sea
...


Minerals replaces
the calcite in the
shell
...


Fossils are Formed in Various Ways:
- From the hard parts of animals that do not decay easily
- From parts of organisms that have not decayed because one or more conditions needed for
decay were absent
- When parts of the organisms are replaced by other materials as they decay
- As preserved traces of organisms, e
...
footprints, burrows
Fossils are found:-

- In quarries
- Warm places
- The top of the mountains
How was the baby mammoth fossilised?
The mammoth was preserved by the cold in the ice and snow because the microbes could not
survive the harsh cold conditions
...
Wooly mammoths
have been found here in almost perfect conditions
...
The resin excludes
oxygen, which would normally allow decay to take place
...
Pete bog man was found preserved in a bog
...
Stellar’s Sea Cow - They were hunted to oblivion for their meat and leather
...
Dodo - Destruction of the forest and habitats
...
Animals food supply could also
run out
...
New Predators - Competition to be at the top of the food chain results in animals killing each
other and new predators killing animals that originally didn't have any threats
...
New Diseases - New diseases came along to wipe out species that already existed
...

Reproduction is presented if there is a physical barrier between species e
...
A river or sea
...

Environmental conditions are different on either side of the Colorado River
...

Mutations will occur which may convert a selective advantage in the different conditions
...

New species May Arise as a Result of:
Isolation - two populations of a species becoming separated e
...
geographically
Genetic Variation - each population has a wide range of alleles that control their characteristics
Natural Selection - In each population, the alleles that control the characteristics which help the
organism to survive are selected
Speciation - The population becomes so different that successful interbreeding is no longer
possible



---