Biology
Revision
B2
BIOLOGY UNIT B2 Topic 1 The building blocks of cells Revision Notes
A cell is the smallets unit of life able to control its own activities, but it relies on the rest of the
organism (if multicellular) or the surroundings (if unicellular) to provide it with raw materials i.e.
nutrients and removal
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1.1 Be able to describe the function of the components of a
bacterial cell including chromosomal DNA, plasmid DNA,
flagella and cell wall (see diagram and notes below).
o Bacterial cells are much smaller than plant or animal
cells with some quite distinct and different features.
o Chromosomal DNA: One long strand of DNA
comprises the single chromosome that controls the
cells functions and the cell division of replication.
 The chromosomal DNA moves freely around
the cytoplasm and is not confined in a distinct
nucleus as in plant and animal cells.
o Plasmid DNA: Plasmids are small hoops of extra DNA
that are separate from the chromosomal DNA.
 Plasmids contain genes that help tolerance
against drugs and can be passed from one
bacteria to another.
 This is how the dangerous bacteria MSRA have
evolved.
o Flagella: The flagellum is a long thin tail like structure that projects out of the body of
the cell, and can rotate to move the bacteria along.
 Some bacterial cells have more than one flagella (flagellum).
 Each flagellum is effectively driven by a tiny biochemical electric motor with
moving parts, mostly made of proteins!
 It is quite a remarkable piece of biochemical engineering - bioengineering!
o Cell wall: The cell contents i.e. the cytoplasm, DNA etc. are all held together within
the cell wall surface membrane which controls the passage of substances in and out
of the cell.
o Cytoplasm: Cytoplasm is a jelly like fluid in which most of the cells chemical
reactions take place with the aid of enzyme catalysts.
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1.2 Be able to describe the function of the
components of a plant cell including chloroplast, large
vacuole, cell wall, cell membrane, mitochondria,
cytoplasm and nucleus (see diagram and notes
below) and know the differences between plant and
animal cells.
o Plant cells are much larger than bacterial
cells, with important differences from animal
cells.
o Chloroplast: The chloroplasts contain the
green chlorophyll molecules which are
involved in the energy absorbing process of
photosynthesis.
 sunlight energy + carbon dioxide +
water ==> sugars e.g. glucose +
oxygen
 Therefore chloroplasts are the site of
food production.
o Large vacuole: The large vacuole in plant cells contains cell sap, a dilute solution of
salts and sugars.
o Cell wall: The rigid cell wall in plant cells is made of cellulose and gives the cell
membrane and contents extra support giving plants their rigidity - their stable 3D
structure.
o Cell membrane: The cell contents i.e. the cytoplasm, nucleus, vacuole, mitochondria,
chloroplasts etc. are all held together by the cell surface membrane which controls
the passage of substances in and out of the cell.
o Mitochondria: The energy releasing chemistry of respiration occurs in the
mitochondria.
 e.g. glucose + oxygen ==> carbon dioxide + water + energy
 Mitochondria are power house of the cells and provides the chemical energy
for any of the cells functions.
o Cytoplasm: Cytoplasm is a jelly like fluid in which most of the cells chemical
reactions take place.
o Nucleus: The cell nucleus contains all the DNA of the genes in the chromosomes
which control the cells functions and the cell division of replication. The nucleus
controls the activities of the cell by sending instructions to the cytoplasm.
o Starch grains: Stored food for respiration
1.3 Be able to describe the function of the
components of an animal cell including cell
membrane, mitochondria, cytoplasm and nucleus
(see diagram and notes below).
o Animal cells are much larger than bacterial
cells, with important differences from plant
cells.
o Cell membrane: The cell contents i.e. the
cytoplasm, nucleus, vacuoles,
mitochondria etc. are all held together by
the cell membrane which controls the
passage of substances in and out of the
cell.
o Mitochondria: The energy releasing
chemistry of respiration occurs in the
mitochondria.
 e.g. glucose + oxygen ==> carbon
dioxide + water + energy
 Mitochondria are power house of the cells and provides the chemical energy
for any of the cells functions.
o Cytoplasm: Cytoplasm is a jelly like fluid in which most of the cells chemical
reactions take place.
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Nucleus: The cell nucleus contains all the DNA of the genes in the chromosomes
which control the cells functions and the cell division of replication. The nucleus
controls the activities of the cell by sending instructions to the cytoplasm.
o Glycogen granules: Stored food for respiration.
o Small vacuoles:
1.4 Be able to describe how plant and animal cells can be studied in greater detail with a light
microscope.
o Microscopes enable you to objects (like microorganisms) which you cannot see with
the naked eye.
o Microscopes using the visible part of the electromagnetic spectrum (visible light) were
invented in the late 16th century and the optical lens systems have been improved
through the following centuries even until today.
o With these light microscopes you can see individual cells and smaller details such as
nuclei and mitochondria in all cells, and chloroplasts in plant cells.
1.5 Be able to demonstrate an understanding of how changes in microscope technology have
enabled us to see cells with more clarity and detail than in the past, including simple
magnification calculations.
o In the 20th century, with advances in atomic physics, the electron microscope was
invented which works off beams of electrons instead of visible light.
o This has enabled the magnification produced by a microscope to be considerable
increased to the point where you can see even smaller structures such as the internal
details of mitochondria, chloroplasts and plasmids (hoops of DNA).
o magnification = length of image / length of object
1.6 Know that a gene is a section of a molecule of DNA and that it codes for a specific
protein.
1.7 Be able to describe a DNA molecule as
o a) two strands coiled to form a double helix
o b) strands linked by a series of complementary base pairs joined together by weak
hydrogen bonds:
 (i) adenine (A) with thymine (T)
 (ii) cytosine (C) with guanine (G)
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1.8 Appreciate how to extract DNA from cells
1.9 Be able to explain how the structure of DNA was discovered, including the roles of the
scientists Watson, Crick, Franklin and Wilkins
1.10 HT only: Be able to demonstrate an understanding of the implications of sequencing the
human genome (Human Genome Project) and of the collaboration that took place within this
project
1.11 Be able to demonstrate an understanding of the process of genetic engineering,
including the removal of a gene from the DNA of one organism and the insertion of that gene
into the DNA of another organism
o This is exemplified by the production of insulin from bacteria.
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1. An appropriate bacteria is selected that will give a good yield of insulin.
2.The bacterial plasmids are extracted from the bacteria.
3. A section of the plasmid DNA is cut by enzymes.
4. The human gene responsible for insulin production is cut from the human
chromosomal DNA with enzymes.
o 5. Other enzymes are used to insert ('splice') the insulin gene in to the bacterial
plasmid DNA.
o 6. The modified plasmids are put back into the bacteria cells.
o 7. The bacteria rapidly reproduce when grown in a fermenter.
o 8. The insulin is extracted and the waste bacterial cells destroyed.
1.12 Discuss an understanding of the advantages and disadvantages of genetic engineering
to produce GM organisms, including:
o a) beta carotene in golden rice to reduce vitamin A deficiency in humans
o b) the production of human insulin by genetically modified bacteria
o c) the production of herbicide-resistant crop plants
1.13 Be able to describe the division of a cell by mitosis as the production of two daughter
cells, each with identical sets of chromosomes in the nucleus to the parent cell, and that this
results in the formation of two genetically identical diploid body cells.
o Cell division my mitosis (diagram above, notes below)
o 1.14 Know that mitosis occurs during growth, repair and asexual reproduction.
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1.15 Know that, at fertilisation, haploid gametes combine to form a diploid zygote (see below).
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1.16 Be able to describe the division of a cell by meiosis as the production of four daughter
cells, each with half the number of chromosomes, and that this results in the formation of
genetically different haploid gametes.
o Cell division my meiosis diagram above, notes below
o 1.17 Know that cloning is an example of asexual reproduction that produces genetically
identical copies
1.18 HT only: Be able to demonstrate an understanding of the stages in the production of
cloned mammals, including:
o a) removal of diploid nucleus from a body cell
o b) enucleation of egg cell
o c) insertion of diploid nucleus into enucleated egg cell
o d) stimulation of the diploid nucleus to divide by mitosis e implantation into surrogate
mammals
1.19 Be able to demonstrate an understanding of the advantages, disadvantages and risks of
cloning mammals
1.20 Know that stem cells in the embryo can differentiate into all other types of cells, but that
cells lose this ability as the animal matures
1.21 Be able to demonstrate an understanding of the advantages, disadvantages and risks
arising from adult and embryonic stem cell research
1.22 Be able to describe how the order of bases in a section of DNA decides the order of
amino acids in the protein
1.23 HT only: Be able to demonstrate an understanding of the stages of protein synthesis,
including transcription and translation:
o a) the production of complementary mRNA strand in the nucleus (diagram below).
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 b) the attachment of the mRNA to the ribosome
c) the coding by triplets of bases (codons) in the mRNA for specific amino acids
d) the transfer of amino acids to the ribosome by tRNA
e) the linking of amino acids to form polypeptides
Points b) to e) are illustrated and explained below
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o 1.24 Be able to describe each protein as having its own specific number and sequence of
amino acids, resulting in different-shaped molecules that have different functions, including
enzymes
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1.25 Be able to demonstrate an understanding of how gene mutations change the DNA base
sequence and that mutations can be harmful, beneficial or neither ('neutral').
1.26 Be able to describe enzymes as biological catalysts.
o A catalyst is substance that speeds up a chemical reaction by lowering the activation
energy of the reaction, that is the threshold energy the reactants must have before
they can change to products on collision. A true catalyst is not used up in the
reaction, but may temporarily change in the course of the reaction, and subsequently
be regenerated to act again. Most chemical reactions ('biochemistry') in living
organisms are catalysed by enzymes, hence their descriptions as 'biological
catalysts'.
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The 'key and lock' mechanism diagram shown above illustrates the function and
regeneration of biochemical catalysts we call enzymes (which often have a complex
protein structure). The catalyst structure is the same at the start and the end of the
reaction, but the permanent chemical change is the reactant substrate molecule
changing into the two new molecules - the reaction products.
1.27 Be able to demonstrate an understanding that enzymes catalyse chemical reactions
occurring inside and outside living cells, including:
o a) DNA replication
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The diagram above gives an extremely simplified summary of how DNA can
self-replicate, with the help of several enzymes.
 Essentially the original DNA double helix is unwound ('unzipped') by one
enzyme E1 to form two template strands.
 Other enzymes e.g. E2, can then select the matching base component (A
<=> T or C <=> G), pairing them up and then zipping up to form the two new
replica double helix strands of DNA completing the replication process.
o b) protein synthesis
o c) digestion
1.28 Be able to describe the factors affecting enzyme action, including:
o a) temperature
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 b) substrate concentration
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c) pH
When the concentration of substrate is high, all the active sites on the
enzymes are occupied and the rate of reaction reaches a maximum and
stays constant.
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The first diagram is typical of many enzymes operating in near neutral
solutions (~pH 7)
 The second diagram shows the wide range of pH that different enzymes can
operate in
 e.g pepsin breaks down proteins in the very acid conditions of the stomach.
 Blood has a pH of ~7.4 and carbonic anhydrase (optimum pH ~7) is found in
red blood cells. This enzyme enables the efficient conversion of carbon
dioxide and water into the carbonic acid and the hydrogen carbonate ion
('bicarbonate ion') and operates in near neutral conditions.
 Trypsin is a protease enzyme from the pancreas that breaks down proteins
(peptides) in the alkaline conditions (~pH 8.5) of the smaller intestine, so its
optimum rate of reaction is around that value.
1.29 Know that enzymes are highly specific for their substrate
1.30 Be able to demonstrate an understanding of the action of enzymes in terms of the ‘lockand-key’ hypothesis
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o 1.31 Be able to describe how enzymes can be denatured due to changes in the shape of the
active site
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o 1.32 Revise any investigations you did on the factors that affect enzyme activity.
BIOLOGY UNIT B2 Topic 2 Organisms and energy Revision Notes
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2.1 Know that respiration is a process used by all living organisms that releases the energy in
organic molecules.
2.2 Be able to explain how the human circulatory system facilitates respiration, including:
o a) glucose and oxygen diffuses from capillaries into respiring cells
o b) carbon dioxide diffuses from respiring cells into capillaries.
2.3 Be able to define diffusion as the movement of particles from an area of high
concentration to an area of lower concentration.
2.4 Be able to demonstrate an understanding of how aerobic respiration uses oxygen to
release energy from glucose and how this process can be modelled using the word equation
for aerobic respiration.
o glucose + oxygen ==> water + carbon dioxide (+ energy)
2.5 Revise any investigations on the effect of exercise on breathing rate and heart rate.
2.6 Be able to explain why heart rate and breathing rate increase with exercise.
2.7 Be able to calculate heart rate, stroke volume and cardiac output, using the equation
cardiac output 5 stroke volume 3 heart rate
2.8 Be able to demonstrate an understanding of why, during vigorous exercise, muscle cells
may not receive sufficient oxygen for their energy requirements and so start to respire
anaerobically
2.9 Be able to demonstrate an understanding of how anaerobic respiration releases energy
from glucose and how this process can be modelled using the word equation for anaerobic
respiration
2.10 Know that the process of anaerobic respiration releases less energy than aerobic
respiration
2.11 Be able to describe how a build-up of lactic acid requires extra oxygen to break it down.
o Know this is called excess post-exercise oxygen consumption or EPOC (formerly
known as oxygen debt)
2.12 Be able to explain why heart rate and breathing rate remain high after exercise
2.13 Be able to describe how the structure of a leaf is adapted for photosynthesis, including:
o a) large surface area
o b) containing chlorophyll in chloroplasts to absorb light
o c) stomata for gas exchange (carbon dioxide, oxygen and water vapour)
2.14 Be able to demonstrate an understanding of how photosynthesis uses light energy to
produce glucose and how this process can be modelled using the word equation for
photosynthesis
o water + carbon dioxide (+ sunlight) ==> glucose + oxygen
2.15 Be able to demonstrate an understanding of how limiting factors affect the rate of
photosynthesis, including:
o a) light intensity
o b) CO2 concentration
o c) temperature
2.16 Revise any investigations on how factors, including the effect of light intensity, CO2
concentration or temperature, affect the rate of photosynthesis
2.17 Be able to explain how the loss of water vapour from leaves drives transpiration
2.18 Be able to explain how water, glucose and mineral salts are transported through a plant,
including: a mineral uptake in roots by active transport b the role of the xylem and phloem
vessels
2.19 Be able to describe how root hair cells are adapted to take up water by osmosis
2.20 Be able to define osmosis as the movement of water molecules from an area of higher
concentration of water to an area of lower concentration of water through a partially
permeable membrane
2.21 Revise any investigations on osmosis you did.
2.22 Revise any investigations on the relationship between organisms and their environment
using fieldwork techniques
2.23 Revise any investigations on the distribution of organisms in an ecosystem, using
sampling techniques including:
o a) pooters
o b) sweep nets/pond nets
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c) pitfall traps
d) quadrats
and measure environmental factors including:
 e) temperature
 f) light intensity
 g) pH
BIOLOGY UNIT B2 Topic 3 Common systems Revision Notes
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3.1 Be able to evaluate the evidence for evolution based on the fossil record
3.2 Be able to explain why there are gaps in the fossil record, including:
o a) because fossils do not always form
o b) because soft tissue decays
o c) because many fossils are yet to be found
3.3 HT only: Be able to explain how the anatomy of the pentadactyl limb provides scientists
with evidence for evolution
3.4 Be able to describe growth in terms of increase in size, length and mass
3.5 Be able to interpret growth data in terms of percentile charts
3.6 Be able to explain how cell division, elongation and differentiation contribute to the growth
and development of a plant
3.7 Be able to explain how cell division and differentiation contribute to the growth and
development of an animal
3.8 Know the structure and function of the following parts of the blood, including:
o a) red blood cells
o b) white blood cells
o c) plasma
o d) platelets
3.9 Be able to describe the grouping of cells into tissues, tissues into organs, and organs into
organ systems
3.10 Be able to explain how the structure of the heart is related to its function, including:
o a) the four major blood vessels associated with the heart (pulmonary artery,
pulmonary vein, aorta, vena cava)
o b) left atrium and ventricle to pump oxygenated blood
o c) right atrium and ventricle to pump deoxygenated blood
o d) valves to prevent backflow (names not required)
o e) left ventricle has a thicker muscle wall than the right ventricle
o f) the direction of blood flow through the heart
3.11 Be able to describe how the circulatory system transports substances around the body,
including:
o a) arteries transport blood away from the heart
o b) veins transport blood to the heart
o c) capillaries exchange materials with tissues
3.12 Be able to describe the functions of the parts of the digestive system, including:
o a) mouth
o b) oesophagus
o c) stomach
o d) small and large intestines
o e) pancreas
o f) liver
o g) HT only: gall bladder
3.13 Be able to explain the role of the muscular wall of the alimentary canal in peristalsis
3.14 Be able to explain the role of digestive enzymes, including:
o a) carbohydrases, including amylase, which digest starch to simple sugars
o b) proteases, including pepsin, which digest proteins to amino acids
o c) lipase, which digests fats to fatty acids and glycerol
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3.15 HT only: Be able to explain the role of bile in neutralising stomach acid and emulsifying
fats
3.16 HT only: Be able to explain how the structure of villi (large surface area, single layer of
cells and capillary network) allows efficient absorption of the soluble products of digestion
3.17 Revise any investigations on the effect of different concentrations of digestive enzymes,
using and evaluating models of the alimentary canal
3.18 Be able to evaluate the evidence for the claimed benefits of the use of functional foods
as part of a healthy diet, including:
o a) probiotics containing Bifidobacteria and lactic acid bacteria Lactobacillus
o b) prebiotic oligosaccharides
o c) plant stanol esters