Summary of each specification point for Edexcel B2.

1. B2 Topic 2

2. B2.1 – Plant and Animal Cells
7 Organelles Function
Cell Membrane Controls movement into and out of the cell.
Nucleus Contains DNA. Controls the cell
Cytoplasm Where chemical reactions take place.
Mitochondria Where respiration occurs.
Cell Wall Made of CELLULOSE. Supports the cell.
Vacuole Contains CELL SAP. Helps support the plant by keeping the cell rigid
Chloroplast Contains CHLOROPHYLL. Absorbs LIGHT. Where photosynthesis takes place
Plant and animal cells can be
studies in greater detail using a
light microscope.
Light passes through a thin slice of
the specimen. Lenses magnify the
specimen many times.

3. B2.2 – Inside Bacteria
4 Organelles Function
Chromosomal DNA A giant loop of DNA containing most of the genetic material.
Plasmid DNA Small loops of DNA that carry extra information.
Flagella Long whip like structures that aid movement.
Cell Wall Provides support but is more flexible than a plant. Not made
of cellulose.
2 types of DNA
Microscopes have improved in last 350 years.
Light microscopes can magnify 1500x.
Electron microscopes can magnify 2000000x.
Electron microscopes produce very clear
images.
Electron microscopes show more detail of the
specimen.

4. B2.3 - DNA
Key Definition
A gene is a section of DNA that codes
for a specific protein.
DNA is made up of two strands
coiled to form a double helix.
The two strands are linked by
complementary bases held together
by weak hydrogen bonds.
Adenine (A) pairs with Thymine (T)
Cytosine (C) pairs with Guanine (G)

5. B2.4 – Extracting DNA
1. Chop onion or peas into chunks.
2. Grind in a pestle and mortar.
3. Mix together with washing up liquid, salt and water and
stir.
4. Incubate the mixture at 60 degrees Centigrade for 15
minutes in a water bath.
5. Filter the mixture through filter paper into a boiling tube.
6. Take ice cold alcohol and pour it slowly down the side of
the boiling tube. The alcohol will form a transparent layer
on top of the liquid, as the alcohol is less dense.
7. You will see the DNA between the two liquid layers.

6. B2.5 – DNA Discovery
London - Maurice Wilkins & Rosalind Franklin using X-rays to
study DNA structure. From the patterns made they could work
out how the atoms were arranged.
Cambridge – Watson & Crick were building a model of DNA using
data from other scientists. They were given a copy of Franklins
photographs which enabled them to crack the code. Franklin
didn’t know they had the photo.
Watson and Crick published their paper with the structure of
DNA but didn’t acknowledge the photograph they used
Watson and Crick were awarded the Nobel Prize with Maurice
Wilkins but Rosalind Franklin had already died so did not get the
prize.

7. B2.5 – DNA Discovery
The Human Genome Project –
International Project.
3 billion bases that make up the
human genome were sequenced.
It took 13 years and scientists
collaborated using IT to store and
share data.
All humans have 99.9% of their
DNA in common.
5 Implications of the HGP
1. Improved genetic testing for
disorders.
2. New ways of finding new
genes that may increase risk
of certain diseases.
3. New treatments and cures
for diseases.
4. New ways of looking at
changes in the genome over
time.
5. Personalised medicines that
work with a particular
genotype.

8. B2.6 – Genetic Engineering
Know this process!
Definition - The process of removing a gene from one organism and inserting it into
the DNA of another.

9. B2.6 – Genetic Engineering
Example Advantages Disadvantages
Beta carotene in
golden rice to
reduce vitamin
A deficiency in
humans
1. Beta carotene used to make vitamin
A
2. Vitamin A will reduce death and
blindness.
1. Could cross breed with wild rice and
contaminate wild rice DNA
2. Levels of beta carotene in Golden
Rice might not be high enough to
make a difference
3. Can be expensive to buy
4. Produces sterile seeds so farmers
have to buy them every year
The production
of human insulin
by GM bacteria
1. Can be used by vegans
2. Supply not affected by animal
diseases
3. Supply not affected by demand for
meat
4. Can be made in vast quantities
5. Cheaper
1. Bacteria produce insulin slightly
differently so may not work for
some people
The production
of herbicide
resistant crops
1. Reduces amount of crop spraying 1. Herbicide resistant weeds can
develop
2. Cross pollination with wild plants
3. Potential loss of biodiversity

10. B2.7 – Mitosis and
Meiosis
Mitosis
• The production of two
daughter cells with identical
sets of chromosomes in the
nucleus as the parent cell.
• Results in the formation of
two genetically identical
diploid cells.
• Occurs during growth and
repair and asexual
reproduction
Meiosis
• The production of four
daughter cells, each with
half the number of
chromosomes as the parent
cell.
• Results in the formation of
genetically different haploid
gametes.
• Occurs when making
gametes only.
Definitions
Haploid – Having one set of chromosomes.
Diploid – Having two sets of chromosomes.
Gamete – the sex cells (sperm and egg)
At fertilisation, haploid gametes join to form a diploid zygote.

11. B2.8 - Clones
How to produce a clone
1. Remove a diploid nucleus
from a body cell
2. Enucleate an egg cell
3. Insert diploid nucleus into
enucleated egg cell.
4. Stimulate the diploid
nucleus to divide by mitosis.
5. Implant into surrogate
mother.
Cloning – An example of asexual
reproduction.
Enucleate – Remove the nucleus

12. B2.8 - Clones
Advantages of
Cloning
Disadvantages of
Cloning
Risks of Cloning
1. Can make a
genetically
identical copy of
an animal with
desirable
characteristics.
2. Can be used to
make copies of
GM animals to
guarantee all
offspring have
the trait.
1. Cloned animals
often die young.
2. Cloned animals
often age more
quickly.
3. Complicated
process.
1. Very few
embryos develop
properly resulting
in deformities.

13. B2.9 – Stem Cells
Advantages of Stem Cell
Research
Disadvantages of Stem Cell
Research
Risks of Stem Cell Research
1. Embryonic stem cells can
develop into almost every
type of human cell.
2. Bone marrow stem cells
can be used to treat
lukaemia.
3. Adult stem cells may be
used in future instead of
embryonic stem cells.
1. Embryonic stem cells can
come from leftover
embryos from fertility
treatments.
2. Risk of rejection if not
from a patients own stem
cells.
3. Could lead to tumours
forming.
1. Technology could be used
illegally.
2. Risk of the unknown – long
term effects may not be
shown for years.
Key definitions
Stem Cell - An unspecialised cell that can divide to produce more stem cells or
different types of specialised cell.
Differentiate – Become specialised.
Embryonic Stem Cell – Can differentiate into almost any cell type.
Adult Stem Cell – Can differentiate into only a few cell types.
Specialised Cell – a cell with a particular function e.g. neurone, red blood cell.

14. B2.10–ProteinManufacture

15. B2.10 Protein Manufacture
Transcription
1. DNA double helix unzips.
2. The complementary mRNA strand is made in the nucleus and
passes out through a pore.
Translation
1. mRNA attaches to the ribosome.
2. A triplet of bases on the mRNA (codon) code for a specific amino
acid.
3. tRNA transfers amino acids to the ribosome.
4. Amino acids link together to form polypeptides.
RNA is single stranded but DNA is double stranded.
RNA contains Uracil (U) instead of thymine (T)
Each amino acid is
coded for by 3
specific bases. DNA
is a triplet code.

16. B2.11 - Mutations
1. Each protein has its own specific number and
sequence of amino acids.
2. This is coded for by the DNA.
3. Therefore, each protein is a different shape and
has a different function e.g. an enzyme.
4. Mutations change the sequence of the bases,
and therefore the shape of the protein.
5. Most mutations are harmful.
6. Radiation and some chemicals in cigarette
smoke are mutagens and cause mutations.
Mutation – A change in the sequence of bases in the
genetic code.

17. B2.12 - Enzymes
These are examples of enzyme catalysed reactions:
1. DNA Replication – One enzyme unzips the two strands
of DNA, the other joins the new bases together to
make the new double stranded molecule.
2. Protein Synthesis – RNA Polymerase makes the mRNA
strand from the DNA template.
3. Digestion – Many enzymes break larger molecules
down into smaller ones in digestion. This happens
outside of the body. Stain digesting enzymes in
washing powders break down stain in clothes.
Microorganisms excrete enzymes onto food to break
them down outside the body and then absorb the
products.
Enzymes are biological catalysts. They speed up reactions.

18. B2.13 – Enzymes and Temperature
Factors that affect enzyme activity:
1. Temperature
2. pH
3. Substrate Concentration.
Enzymes are SPECIFIC to their substrate. They only catalyse
specific reactions in specific conditions. They have a specific
shaped active site.
Enzyme activity can be measured by measuring the speed at
which a product is made e.g. a gas, or the speed at which a
substrate is used up e.g. stain digestion.

19. B2.14 – Enzyme Action
As temperature
increases, so does
enzyme activity, up to
40oC. After 40oC the
active site is denatured
and the reaction stops.
As substrate concentration
increases, so does enzyme
activity, up to a point where the
number of active sites becomes
limiting. The only way to speed
up the reaction after this is to
increase the number of active
sites.
Enzymes will only work
at a specific pH. Either
side of this optimum
pH, the enzyme will
denature and not
work.
Enzymes can never be killed. They can
only be denatured, which is where the
shape of the active site changes.

20. B2.14 – Enzyme Action
Enzymes work like a lock and key
Lock and Key Enzyme and Substrate
One key will only fit one lock. One substrate will only fit one enzyme.
The key fits the lock. The substrate fits the active site
The key unlocks the lock. The substrate is changed in the enzyme
Wrong key won’t fit the lock. Wrong substrate won’t fit the active site.

21. B2.15 Aerobic Respiration.
• All organisms are made of cells
• Energy released by respiration
• Cells that move more need more energy.
• Exercise = more energy needed.
Key Terms:
Respiration - the release of energy from
food molecules that act as fuel for the cell.
Diffusion - when substances move from an
area of high concentration to an area of low
concentration.
Glucose + Oxygen = Carbon Dioxide + Water
Aerobic respiration = uses oxygen to release energy from glucose.
How does it get delivered?
• Glucose and oxygen diffuse from capillaries to respiring cells
• Carbon dioxide diffuses from respiring cells to capillaries
• Capillaries - smallest vessel that carries blood between cells/ one cell thick
• Substances move by diffusion down a concentration gradient = the diffusion
pathway.

22. • Respiring cells = oxygen and glucose levels fall as they are used up in
aerobic respiration/ Carbon dioxide levels increase.
• Gas exchange = the transfer of gases.

23. B2.16 investigating The effects of
exercise.
• Exercise = increase heart rate and has to pump
blood faster to the muscles.
• Causes breathing rate to increase and get deeper.
Why?
• Cells need more oxygen and glucose as they need
more energy.
• Cells produce more carbon dioxide as a result
which needs to be removed.

24. B2.17 Anaerobic respiration
• Anaerobic respiration = respiration without oxygen
• Glucose is broken down to supply energy to the muscles
• Releases less energy then aerobic and produces Lactic Acid
• Amount of blood pumped around the body depends on the stroke volume and the
heart rate.
• Exercise = increase in heart rate and stroke volume.
• Lactic Acid needs to be broken down = oxygen used to break it down into carbon
dioxide and water.
• The requirement of this oxygen to break down the lactic acid is called excess post-
exercise oxygen consumption (EPOC)
Glucose  lactic acid
Cardiac output = stroke
volume x heart rate.

25. B2.18 Photosynthesis.
• Photosynthesis = plants make their own food
• Uses light energy to produce glucosefrom carbon dioxide and water
• Glucose stored as starch
• Starch = lots of glucose molecules joined together.
• Digestion breaks down starch = glucose
• Chlorophyll = green found in chloroplasts absorbs light for
photosynthesis.
• Variegated leaves = the green parts of a leaf contain the chlorophyll.
Carbon dioxide + water  glucose + oxygen
Light and chlorophyll

26. 2.20 Factors that effect the rate of
photosynthesis.
3 factors that effect photosynthesis.
• Carbon dioxide
• Light
• Temperature
• All 3 are needed at optimum amount for photosynthesis to be at its best.
• The limiting factor is the one that is in short supply…..you may have lots of CO2 the right
temperature but little light this means photosynthesis will be slow.
Limiting factor =
something can affect
the rate of
photosynthesis.

27. Adaptations of a leaf.
Upper epidermis = tightly packed cells = lots of
chloroplasts = lots of photosynthesis.
Air spaces = provide large surface for cells to
exchange with gases in the air.
Lower epidermis = contain stomata.
Stomata = open and close to allow gases into
the leaf. Located underside of the leaf.
Open in response to light.
Allow Carbon dioxide in and lets out oxygen
and water vapour.
3 Adaptations
Has stomata for gas exchange
(carbon dioxide, oxygen,
water vapour)
Contains chlorophyll in
chloroplasts to absorb light.
Large surface area to absorb
most amount of light.

28. Root HairCell
• Job of root = anchor plant
and take up nutrients.
• Root hair found on surface
of root.
• Role – to absorb water
and dissolved minerals.
• Adaptation = large surface
area.
B2.21 Water Transport
• Roots absorb nitrates and mineral ions
dissolved in water by Active transport.
This needs energy from respiration
• Water transported by xylem
• Nutrients transported by phloem
Key Definitions
• The loss of water from the leaves drives
transpiration.
• Transpiration – the movement of water
through a plant and the loss of water
throught he leaves.
• Osmosis = movement of water from an area
of low concentration to an area of high
concentration through a partially permeable
membrane.

29. B2.22 Investigating Osmosis
Osmosis
Water can move across cell membranes because
of osmosis. For osmosis to happen you need:
two solutions with different concentrations and
a partially permeable membrane to separate them

30. B2.23 Organisms and their
environment
Key Terms
• Environment = an organisms
surroundings including the soil, air,
water and other organism in the area.
• Biodiversity = the different plants and
animals in an area.
• Ecosystem = an area in which all the
living organisms and all the non living
organism form a relationship in order
to survive.
• Habitat = where the plants and
animals are found/living.
• Population = the number of animals in
a given area.
• Sampling = looking at small proportion
of the plants and animals.
Sampling techniques =
• 1) Pooter = used to catch animals.
• 2) Sweep net = can catch flying
animals.
• 3) Pond net = to catch aquatic
animals.
• 4) pit fall traps = buried in the
ground…the organisms fall in.
• 5) quadrats = used to sample the
population size of plants = random
sampling or systematic sampling. =
placing the quadrat at regular
intervals along a line.

31. B2
Topic 3 Common Systems

32. B2.25 Fossils and evolution
Keywords
• Fossil record – The collection of fossils identified from different periods of time that can be
interpreted to form a hypothesis about the evolution of life on Earth.
• Fossil – The preserved traces or remain of an organism which lived a very long time ago
• Pentadactyl – five fingered organism
Facts:
• The moon is 30 ‘earths’ away
• The sun is 11,000 ‘earths’ away
Fossils
• Fossils from different periods of time show organisms have changed gradually = evolution.
• Fossil record has gaps
– Soft tissues decay not forming fossils
– Hard parts of organisms could have been destroyed
– Many fossils are buried too deep to be found
• Scientists using incomplete data sometimes make mistakes
• More fossils = more accurate conclusions
Evidence for Evolution
• Internal bones of all vertebrate’s limbs are similar
• Fossils of limbless vertebrates have the same five fingered structure
• All vertebtates evolved from one common ancestor
• Evolution of the limbs is due to adaptation to how the organisms lived and moved,

33. B2.26 Growth
Keywords
• Percentile – The value of a variable below which a certain percentage of observations fall.
• Stem Cell – An unspecialised cell that can divide to produce more stem cells or different kinds of specialised cells
• Differentiate – Specialise, develop into different kinds of cell, as in cells that become nerve, muscle or bone cells
• Elongation – getting longer
Facts
• Growth is when an organisms
increases in size, length and
mass
• To monitor growth of babies we
check
– Head circumference
– Weight
– Height
• Each child is compared to a chart
to determine which percentile of
the population they are in.
• Growth involves 2 things
– Increase in the number
of cells
– Increase in the size of
cells
Growth in Plants
• Grow all through their lives
• Cells divide in the Meristem – behind the tip of the root and shoot
• Cells also elongate
• Older meristem cells differentiate to become specialised for example:
– Palisade leaf cell
– Root hair cell
Growth in Animals
• Cell division
• Animals stop growing when they become adults
• Stem cells are undifferentiated
• Stem cells can specialise into all other cells
• Adults have very few stem cells (only in blood and
skeletal tissues)
• Most animals cannot regrow limbs or body parts.

34. Components
• Plasma
– Fluid part of blood
– Transports carbon dioxide, hormones and waste
– Pale yellow
• Red blood cells
– No nucleus = more room for haemoglobin
– Made in the bone marrow.
– Contain red pigment haemoglobin which carries oxygen
Oxygen + Haemoglobin Oxyhaemoglobin
– Oxygen is carried in the blood to the tissues for aerobic respiration
– Biconcave disc = large surface area to volume ratio for faster diffusion of oxygen
• White blood cells
– An important part of the immune system
– Some produce antibodies (proteins that bind to microbes and destroy them)
– Others surround and destroy foreign cells
– All have a nucleus
– Made in the bone marrow
– All have a nucleus
• Platelets
– Tiny fragments of cells (no nuclei)
– Clump together to form clots
– Protect the body by stopping bleeding and forming a scab to stop microbes entering.
B2.27 Blood

35. B2.28 The heart
• Deoxygenated blood (low
oxygen levels)
• Pumped to the lungs (by
right ventricle) to collect
oxygen
• Oxygenated blood
returns to heart (Left
side)
• Pumped to the body cells
and tissues (by left
ventricle)
• Left and right side work
together at the same
time
• Valves prevent backflow
of blood
• Tendons stop valves
turning inside out
Septum
Thicker wall as it
pumps blood all
around the body

36. B2.29 The circulatory system
3 types of blood vessel:
Arteries
• Carry blood away from the heart
• Have thick muscular walls
• Have small internal lumen
• Blood under high pressure
Veins
• Carry blood to the heart
• Thin walls
• Larger internal lumen
• Blood under low pressure
• Valves to prevent blood flowing
backwards
Capillaries
• Wall is one cell thick
• Very low blood pressure
• Allows diffusion between blood
and tissues

37. B2.30 The
digestive
system
churns
Peristalsis
• Muscles contract
in waves to move
food along the
alimentary canal (
a muscular tube
running from
your mouth to
your anus)

38. B2.31 Breaking
down food
Keywords
Enzyme – a protein molecule made by living cells that speeds up the rate of a
reaction
Emulsion – a mixture in which particles of one liquid are suspended in another
liquid.
Digesting proteins Digesting
Carbohydrates
Digesting Fats
Enzyme
involved
Proteases (e.g.
pepsin)
Carbohydrases (e.g.
amylase)
Lipases
Broken down
into…
Amino acids Simple sugars
(glucose)
Glycerol and Fatty acids
Where it occurs Stomach first then
small intestine
Mouth and small
intestine
Small Intestine
Additional
features
Pepsin has an
optimum pH of 2
(perfect for
stomach acid)
Amylase is
denatured by
stomach acid
• Bile from the gall bladder
breaks down large fat globules
into droplets with a larger
surface area to help lipase.
• We say bile emulsifies the fat.
• Bile also neutralises the
stomach acid.

39. B2.32 Villi
Inside the Small Intestine
1. Digested food passes into blood by diffusion
2. Bigger surface areas = more diffusion
3. Finger-like folds called Villi increase surface area of small intestine
Features of a Villus to speed up diffusion
1. Good network of capillaries moving absorbed nutrients
2. Low concentration of food
3. Steep concentration gradient maintained
4. Wall is a single cell layer (shorter distance
to diffuse)
Keywords
Villi – finger like projections in the small intestine.
Diffusion – movement of particles from an area of high concentration to
an area of low concentration down a concentration gradient.

40. B2.34 Probiotics and Prebiotics – Functional foods
Prebiotics
• Substances the body cannot digest
• They act as food for the beneficial bacteria
• Oligosaccharides are a common form of prebiotic (contained in tomatoes, onions and asparagus)
• Also found in specially made dairy foods and sold as capsules
• Increasing evidence supports their positive effect on health
Plant Stanol Esters
• Oily substances in plants
• Stop the small intestine absorbing cholesterol
• Lowers blood cholesterol
• Use in many foods like yogurt and spreads.
Probiotics
• Live bacteria – friendly or beneficial
• Bifidobacteria or Lactobacillus
• They produce lactic acid in your gut and companies claim they improve health
• NOT ENOUGH EVIDENCE to support the claims they are effective