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A LEVEL BIOLOGY REVISION TEXT WITH
DETAILED ANSWERS
Describe how two-way chromatography is carried out
...
[2] - CorreCt Answers -Spreads spots/polypeptides out more/
make sure spot only contains one substance;

Explain how inhibitors affect the rate of enzyme-controlled reactions
...
[5] - CorreCt Answers -Rate of reaction
increases; Increasing temperature increases rate of movement of
molecules/ kinetic energy; Collide more often/substrate enters active site
more often/more enzyme-substrate complexes formed; Up to optimum;
Rate of reaction decreases; High temperatures cause denaturation/loss of
tertiary structure/3D structure; By breaking specified bonds (not peptide
bond); Active site altered/substrate cannot bind/fit/

An enzyme catalyses only one reaction
...
[2] - CorreCt Answers Active site / enzyme not complementary; Active site changes (shape) / is
flexible; (Change in enzyme allows) substrate to fit / E-S complex to form;

Describe one way that the lock and key model is different from the induced
fit model
...
[3] - CorreCt Answers -(change in pH) leads to breaking of bonds
holding tertiary structure/ changes charge on amino acids;
enzyme/protein/active site loses shape/denatured; substrate will not bind
with/fit active site; fewer/no ES complexes formed;

A protein molecule contains 150 amino acids
...
[3] CorreCt Answers -Prokaryotic cells do not have a nucleus / have genetic
material in cytoplasm; DNA in loop / ring; Not associated with proteins /
do not have chromosomes /chromatin / do not divide by mitosis; Smaller
ribosomes; No membrane-bound organelles; Such as mitochondria /

lysosomes / endoplasmic reticulum / Golgi / chloroplasts; Prokaryotic cells
may have mesosomes; Prokaryotic cells smaller; May be enclosed by
capsule;

What is the function of: a)Ribosome b)Smooth ER c)Golgi apparatus d)
Chloroplast e)Mitochondria [5] - CorreCt Answers -a)Protein synthesis
b)Lipid synthesis and transport c)Processing and packaging proteins for
secretion d)Photosynthesis e)Aerobic respiration to produce ATP

Explain the advantages and limitations of using a transmission electron
microscope [5] - CorreCt Answers -Advantages: Small objects can be seen;
TEM has high resolution as wavelength of electrons shorter; Limitations:
Cannot look at living cells as cells must be in a vacuum; must cut section /
thin specimen; Preparation may create artefact; Does not produce 3D or
colored image;

Why an electron microscope can be used to produce images [2] - CorreCt
Answers -EM gives high resolution due to short wavelength of electrons;

Explain how viruses cause damage to cells
...
[5] CorreCt Answers -Cell homogenisation to break open cells; 1
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Filter to remove (large) debris /

whole cells; 2
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Use isotonic solution to prevent
damage to mitochondria / organelles; Keep cold to prevent / reduce
damage by enzymes / use buffer to prevent protein / enzyme denaturation;
Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments /
heavy organelles; Re-spin (supernatant / after nuclei / pellet removed) at
higher speed to get mitochondria in pellet / at bottom
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[2] - CorreCt Answers -Nucleus; mitochondria;
chloroplast, Golgi, RER; SER; centrioles

Describe the fluid-mosaic structure of a cell surface membrane
...
to intrinsic and
extrinsic, unqualified, gains 1 mark);Detail of channel proteins / protein
shapes / glycoproteins;Presence of cholesterol between phospholipids
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(6/10 marks) - CorreCt
Answers -1
...
Small molecules/water/gases move through phospholipid
layer/bilayer;3
...
Some proteins are gated;5
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Carriers
identified as proteins;7
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Carriers associated with active transport/transport with ATP/pumps;9
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Correct reference to cytosis;

Describe the role of the enzymes of the digestive system in the complete
breakdown of starch
...
Amylase;2
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Maltase;4
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Hydrolysis;6
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(6/9 marks) 1
...
long / folds increase surface
area / time for absorption;3
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short diffusion pathway;5
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lacteal for absorption of
digested fats;7
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mitochondria
supply ATP / energy for active transport;9
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(4 marks) - CorreCt Answers -1
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monoglycerides / micelles/fatty acids move into
epithelial cells;3
...

chylomicrons move into lacteals / lymph;

Describe and explain the role of facilitated diffusion in the absorption of
digested food by the ileum
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movement
along / down concentration gradient;2
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monosaccharides or named / amino acids move into epithelial
cells;

Describe and explain the role active transport in the absorption of digested
food by the ileum
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movement against
concentration gradient;2
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reference to carrier
proteins;4
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reference to co-diffusion e
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glucose and NaCl;6
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Sugar-phosphate backbone: provides stability &
protects bases 2
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Complementary base pairing (A-T and G-C) makes
replication more accurate 4
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Many hydrogen bonds in the DNA molecule:
stable 6
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Helix/coiled:
compact;

Compare DNA Vs RNA (6/ 10marks) - CorreCt Answers -Similarities:
Contain phosphate Made up of nucleotides Contains organic bases (A, C
and G) (not T as it is replaced by U in RNA) Pentose sugar (3 max)
Differences RNA single stranded RNA has non-coding strands (introns)
removed Ribose sugar in RNA deoxyribose in DNA U in ribose replaces the
T 3 types of RNA, only one DNA Smaller than DNA (3 max)

Explain why specific base pairing is important in DNA replication
...
Explain how
...
DNA replicated; Reject: DNA replication in the wrong
stage 2
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(Ref to) two identical / sister
chromatids; 4
...
Note: sister chromatids move to opposite poles / ends = 2
marks for mp 3 and mp 4 Reject: meiosis / homologous chromosomes /
crossing over or events in wrong stage

Describe the features which would help you to recognise when a cell is in i)
metaphase of mitosis; ii) in anaphase of mitosis (4/6 marks) (i) - CorreCt
Answers -Chromosomes or chromatids on equator / in middle of cell; Of
spindle (once); No nuclear membrane (once only)
...


Describe what happens to the chromosomes during each of the following
stages of mitosis
...
Give reasons why
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Growth / increase in cell number; 2
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Genetically identical cells; 4
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(4 marks) - CorreCt Answers -Meiosis halves the number of
chromosomes; Restoration of diploid number at fertilisation; Introduces
variation;Correct reference to natural selection / survival;

Suggest how the proportion of dividing cells in a thin section could be
determined
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Describe how meiosis
causes this variation and explain the advantage of variation to the species
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Crossing-over; [IGNORE any wrong ref
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Independent / random assortment / orientation / segregation
of (homologous) chromosomes in meiosis I; 3
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Different adaptations / some better adapted; 5
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To reproduce; 7
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Allows for
changing environment / different environment / example described;

Describe what happens to chromosomes in meiosis
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Chromosomes shorten / thicken / condense; 2
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Crossing-over / chiasma formation; 4
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(At) equator / middle of cell;(*) 6
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(Homologous) chromosomes move to
opposite poles / chromosomes separate / move apart; (ALLOW 'are pulled
apart') 8
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- CorreCt
Answers -T lymphocytes

Name the lymphocyte present in the humoral response
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Describe how a microbe can be broken down by the process of Phagocytosis
- CorreCt Answers -Pathogen is engulfed by the phagocyte
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Lysosomes fuse
with this vesicle releasing digestive enzymes Lysosome enzymes hydrolyse
the proteins and lipids in the pathogen
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What is a monoclonal antibody? - CorreCt Answers -A hybrid cell from
tumour/cancer and B-lymphocyte form a hybridoma; Antibodies produced
are all the same / from one type of plasma cell; specific to / complementary
to / fits only one antigen;

Describe how B-lymphocytes respond when they are stimulated by
antigens
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(4/6
marks) - CorreCt Answers -DNA copy made (of viral RNA);Inserted into
host DNA / chromosomes;(Uses viral DNA to) make viral
proteins/particles;Makes viral RNA;(Host) cell makes new
viruses;"Budding off" / wrapped in cell membrane;

Define Mass Flow - CorreCt Answers -Mass flow is the bulk movement of
liquids (and gases) due to a pressure difference
...

When blood passes through the lungs the pressure is reduced
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The thickness of the aorta wall changes all the time during each cardiac
cycle
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(5 marks) - CorreCt Answers -1
...
Because ventricle/heart contracts / systole / pressure increases; 3
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Because ventricle relaxes / heart relaxes /diastole /
pressure falls; 5
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(3 marks) CorreCt Answers -artery has muscle artery has elastic tissue to withstand
pressure / capillary only one cell thick with pores for exchange

Describe and explain four ways in which the structure of a capillary adapts
it for the exchange of substances between blood and the surrounding tissue
- CorreCt Answers -1
...
Single cell
thick/thin walls, reduces diffusion distance;3
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Fenestrations, allows some larger molecules
through; 5
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Narrow lumen, reduces flow rate giving more
time for diffusion;7
...


Explain how tissue fluid is formed and how it may be returned to the
circulatory system
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(hydrostatic) pressure of blood
high at arterial end;2
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proteins/large molecules remain;4
...

water moves back into venous end of capillary (reject tissue fluid);6
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lymph system collects any excess tissue fluid;8
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- Atrium
muscles contract- Further increases pressure- Remaining blood forced into
ventricles2) Blood enters ventricle- increase in volume of blood increases
the pressure in the ventricles- Pressure in ventricle greater than in atriumatrioventricular valve closes
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- Blood enters aorta/ pulmonary artery- Blood is
pumped to body (left) or lungs (right)4) Ventricle muscles relax- Pressure
in ventricle is less than in aorta/ pulmonary artery- Semi lunar valves close

How is the cardiac cycle controlled? (6marks) - CorreCt Answers -(SAN)
myogenic; Electrical Impulse (spreads over atria and) produces atrial
contraction; Delay at AVN; Electrical impulse is prevented from passing to
the ventricles by non-conducting tissue Allowing atria to empty before
ventricles contract; Impulse to base of ventricles; Contraction of ventricles
from base up

Describe and explain the mechanism that causes forced expiration
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Contraction of internal intercostal muscles 2
...
Causes decrease in volume of chest/thoracic cavity; 4
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(5 marks) - CorreCt Answers -1 Many alveoli/ alveoli walls folded provide a

large surface area;2 Many capillaries provide a large surface area;3 (So) fast
diffusion;4 Alveoli or capillary walls/ epithelium/ lining are thin/one cell
thick/short distance between alveoli and blood; 5 Flattened/ squamous
epithelium6(So) short diffusion distance/ pathway;7 (So) fast diffusion;8
Ventilation / circulation; 9 Maintains a diffusion / concentration gradient;

Explain how two features of gills allow efficient gas exchange
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(4 marks) CorreCt Answers -1 Exoskeleton / cuticle / outer covering of insect; 2 is
waterproof;3 Insect has a small surface area to volume ratio; 4
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Respiring cells use
up oxygen; 2
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So oxygen diffuses down a concentration gradient from the
tracheae along the tracheoles to the respiring cells
...


Describe how the structure of haemoglobin makes it effective in the
transport of oxygen
...
(6 marks ) - CorreCt Answers -1
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high affinity of
haemoglobin in high partial pressure of oxygen 3
...
oxyhaemoglobin formed; 5
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respiration in
tissues gives high CÓ concentration / high temperature/ high H+
concentration / low pH 7
...

oxyhaemoglobin dissociation at higher partial pressure of carbon dioxide
...


Sketch the oxygen dissociation curve for both animals and explain the
advantage of the position of the mouse curve
...
(at the
tissues at low pp oxygen) the mouse haemoglobin is less saturated with
oxygen / has reduced affinity; oxyhaemoglobin dissociates more readily /
haemoglobin releases oxygen more readily / more oxygen released;
allowing greater demand /respiration rate;

Describe how a high pressure is produced in the phloem near
photosynthesising leaves (3 marks) - CorreCt Answers -Sucrose AT into
sieve tube, water potential becomes lower , water enters phloem by osmosis
from xylem and increased volume increases pressure

How could you measure water uptake in mm3 per minute by a plant? (3
marks) - CorreCt Answers -Potometer, as water moves up plant, an air
bubble is moved along scale, need to measure distance, diameter of
capillary tube and time
...


Give the names of experiments which support mass flow hypothesis CorreCt Answers -Ringing, radioactive tracers

Describe the mass flow hypothesis for the mechanism of translocation in
plants
...
In source / leaf sugars actively
transported into phloem; 2
...
Lowers water potential
of sieve cell / tube and water enters by osmosis; 4
...
Sugars used / converted in
root for respiration for storage
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(6 marks) CorreCt Answers -
...
Stomata open in light → more
water loss; 3
...
Hydrogen-bonding between water molecules /
cohesion ( / described) between water molecules; 5
...
(Xylem) pulled
inwards by faster flow of water / pulled in by tension;

Give three difference between prokaryotic DNA and eukaryotic DNA (3
marks) - CorreCt Answers -DNA of prokaryotes, is short, circular and not
associated with protein
...


Describe how mRNA is produced in the nucleus of a cell
...
Helicase; 2
...
Only one DNA
strand acts as template; 4
...

(Attraction) according to base pairing rule; 6
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Pre-mRNA spliced to remove introns
...
Frequency of
allele increases over time
...
(2 marks) - CorreCt Answers -Crossing over / chiasmata;
Random segregation / independent assortment; In meiosis I and meiosis
II;

When comparing variation in size between two groups of organisms, it is
often considered more useful to compare standard deviations rather than
ranges
...
(2 marks) - CorreCt Answers -Range influenced by
single 'outlier' (accept anomaly) / converse for S
...
; S
...
shows
dispersion/spread about mean; Range only shows highest and lowest
values/extremes; S
...
allows statistical use; Tests whether or not
differences are significant;

Describe how you would investigate the effect of antibacterial chemicals on
the growth of E coli (6 marks) - CorreCt Answers -Aseptic technique/sterile
agar plate, flame neck of culture bottle; Spread plate/controlled volume of
bacteria transferred to plate and spread equally across the surface;

Controlled volume of antibacterial chemical on to filter paper disc; Disc
plated on inoculated agar plate and incubated at 25 degrees C for 2 days;
Diameter of the zone of inhibition measured; Repeat measurements and
mean calculated; Student T test to investigate significance of any difference
between means
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(4 marks) - CorreCt Answers -1
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Stimulates / synchronises mating / production / release of
gametes;3
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Indication of
(sexual) maturity / fertility / receptivity / readiness to mate;5
...


Describe how you would calculate % change - CorreCt Answers -Change /
original x100

Which statistical test do you use if your data is categoric? (i
...
falls into
separate categories like pink and white flowers) - CorreCt Answers -Chi
squared

Which statistical test do you use you want to compare two mean values to
see if they are significantly different from each other or not? - CorreCt
Answers -Student's T test

Which statistical test do you use you want to see if there is a significant
correlation between two variables? - CorreCt Answers -Correlation
coefficient

Write a paragraph using the terms probability and chance if the different or
association from stats results at P 0
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- CorreCt Answers -The probability of the difference or
association being due to chance is less than 5% ; Therefore there is a
significant difference or association between the two means/variables

Write a paragraph using the terms probability and chance if the different or
association from stats results at P 0
...
- CorreCt Answers -The probability of the difference or
association being due to chance is less than 0
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Removal of plant/weeds/pests; 2
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few(er) habitats / niches;3
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(So) fewer food sources / less variety of food
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[3] - CorreCt Answers ,first reducing sugars test; boil with dilute HCl acid then Neutralise with
NaHCǑ, add benedict and heat to 95 degrees C brick red ppt forms if
reducing sugar is present

Describe a chemical test you could carry out to show that a piece of coconut
contains lipids
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[1] - CorreCt Answers -Molecule)
made up of many identical/similar molecules/monomers/ subunits;

Name the reaction which occurs when starch is broken down into maltose
...
[1] CorreCt Answers -H at top right end (instead of OH) / OH at bottom
(carbon 1)

Show two ways in which the structure of cellulose is different from the
structure of starch
...
[3] - CorreCt Answers -Formed from α glucose; Joined by
condensation/ by the removal of a water molecule/ glycosidic bonds;
Between (carbons) 1 and 4 (and 1 and 6); Coiled chain; compact; (Allows)
storage of large amount in a small space; Insoluble so has no effect on
osmosis/water potential; Branches; (Allows) rapid breakdown/release of
glucose / hydrolysis;

The structure of a phospholipid molecule is different from that of a
triglyceride
...
[2] - CorreCt Answers -triglyceride has three
fatty acids and phospholipid has two; no phosphate group present in
triglyceride but present in phospholipid
...
[3] - CorreCt Answers -Alternate β-glucose rotated 180o,

long straight chains, Many hydrogen bonds join (polysaccharide)
chains/molecules to each other / makes microfibrils / gives tensile
strength;

Which elements are found in proteins? [1] - CorreCt Answers -Carbon,
hydrogen, oxygen, nitrogen (sometimes sulphur)

Describe how you would use a biochemical test to show that a solution
contained protein
...
[3] - CorreCt Answers Sequence of amino acids changes; tertiary structure changes/folds in a
different way; bonds form in different places (not peptide);

Starting with mRNA in the nucleus of a cell, describe how a molecule of
protein is synthesised
...
To ribosome; 3
...
Specific tRNA molecule for specific amino
acid; 5
...
Peptide bonds form between amino acids; 7
...
Ribosome moves along mRNA;



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