AQA A level Biology Revision
A protein molecule contains 150 amino acids. What is the total number of peptide bonds in
this molecule? [1] - ANS-149
\An enzyme catalyses only one reaction. Explain why [2] - ANS-(Enzyme has) active site;
Only substrate fits (the active site);
\Calculate the possible number of different combinations of chromosomes following meiosis
(without crossing over) if parent cell contains 22 chromosomes (1 mark) - ANS-211 = 2048
formula 2n
\Compare DNA Vs RNA (6/ 10marks) - ANS-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)
\Define Mass Flow - ANS-Mass flow is the bulk movement of liquids (and gases) due to a
pressure difference.
\Define the term antigen - ANS-An antigen is a molecule (usually protein) that stimulates an
immune response resulting in the production of specific antibodies.
\Describe a chemical test you could carry out to show that a piece of coconut contains lipids.
[3] - ANS-(Crush in) ethanol / alcohol; Add (to) water (Order of adding is critical for this
point); Emulsion / white colour
\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 - ANS-1.Permeable
capillary wall/membrane;2. Single cell thick/thin walls, reduces diffusion distance;3.
Flattened (endothelial) cells, reduces diffusion distance;4. Fenestrations, allows some larger
molecules through; 5. Small diameter/ narrow, gives a large surface area to volume/ short
diffusion distance;6. Narrow lumen, reduces flow rate giving more time for diffusion;7. Red
blood cells in contact with wall/ pass in single file, gives short diffusion distance / more time
for diffusion;
\Describe and explain how an increase in temperature affects the rate of an enzyme
controlled reaction. [5] - ANS-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/
\Describe and explain how cell fractionation and ultracentrifugation can be used to isolate
mitochondria from a suspension of animal cells. [5] - ANS-Cell homogenisation to break
open cells; 1. Accept suitable method of breaking open cells. Filter to remove (large) debris /
whole cells; 2. Reject removes cell walls. 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.
\Describe and explain how the lungs are adapted to allow rapid exchange of oxygen
between air in the alveoli and blood in the capillaries around them. (5 marks) - ANS-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;
\Describe and explain the mechanism that causes forced expiration. (4 marks) - ANS-1.
Contraction of internal intercostal muscles 2. Relaxation of diaphragm muscles/Relaxation of
external intercostal muscles; 3. Causes decrease in volume of chest/thoracic cavity; 4. Air
pushed down pressure gradient;
\Describe and explain the role active transport in the absorption of digested food by the
ileum.(4/6 marks) - ANS-1. movement against concentration gradient;2. energy / ATP
required;3. reference to carrier proteins;4. monosaccharides or named / amino acids moved
into epithelial cells;5. reference to co-diffusion e.g. glucose and NaCl;6. monosaccharides or
named / amino acids move into blood
\Describe and explain the role of diffusion in the absorption of digested food by the ileum. (4
marks) - ANS-1. movement along / down concentration gradient;2. monoglycerides /
micelles/fatty acids move into epithelial cells;3. monoglycerides move from epithelium into
blood;4. chylomicrons move into lacteals / lymph;
\Describe and explain the role of facilitated diffusion in the absorption of digested food by the
ileum. (3 marks) - ANS-1. movement along / down concentration gradient;2. reference to
carrier / channel proteins;3. monosaccharides or named / amino acids move into epithelial
cells;
\Describe how a high pressure is produced in the phloem near photosynthesising leaves (3
marks) - ANS-Sucrose AT into sieve tube, water potential becomes lower , water enters
phloem by osmosis from xylem and increased volume increases pressure
\Describe how a microbe can be broken down by the process of Phagocytosis -
ANS-Pathogen is engulfed by the phagocyte. Forming a vesicle surrounding the pathogen
(called a phagosome). Lysosomes fuse with this vesicle releasing digestive enzymes
Lysosome enzymes hydrolyse the proteins and lipids in the pathogen. Waste materials are
ejected from the cell or presented on cell surface memebrane.
\Describe how B-lymphocytes respond when they are stimulated by antigens.(4 marks) -
ANS-divide by mitosis / form clones; produce plasma cells; (plasma cells) make antibodies;
(plasma cells) produce memory cells;
\Describe how farming effects biodiversity of animals (4 marks) - ANS-1. Removal of
plant/weeds/pests; 2. use of pesticides/ploughing2. few(er) habitats / niches;3. (So) lower
diversity of insects / fewer insect species / fewer insect types;3. (So) fewer food sources /
less variety of food.
\Describe how haemoglobin is involved in absorbing oxygen in the lungs and transporting it
to respiring tissues. (6 marks ) - ANS-1. diffusion of oxygen into haemoglobin in red blood
cells; 2. high affinity of haemoglobin in high partial pressure of oxygen 3. loads / becomes
saturated in lungs / at high ppÓ oxygen; 4. oxyhaemoglobin formed; 5. unloads / low affinity
in low partial pressure of oxygen; 6. respiration in tissues gives high CÓ concentration / high
temperature/ high H+ concentration / low pH 7. dissociation curve shifts to right / 8.
oxyhaemoglobin dissociation at higher partial pressure of carbon dioxide.
\Describe how mRNA is produced in the nucleus of a cell. (6 marks) - ANS-1. Helicase; 2.
Breaks hydrogen bonds; 3. Only one DNA strand acts as template; 4. RNA nucleotides
attracted to exposed bases; 5. (Attraction) according to base pairing rule; 6. RNA
polymerase joins (RNA) nucleotides together; 7. Pre-mRNA spliced to remove introns.
A protein molecule contains 150 amino acids. What is the total number of peptide bonds in
this molecule? [1] - ANS-149
\An enzyme catalyses only one reaction. Explain why [2] - ANS-(Enzyme has) active site;
Only substrate fits (the active site);
\Calculate the possible number of different combinations of chromosomes following meiosis
(without crossing over) if parent cell contains 22 chromosomes (1 mark) - ANS-211 = 2048
formula 2n
\Compare DNA Vs RNA (6/ 10marks) - ANS-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)
\Define Mass Flow - ANS-Mass flow is the bulk movement of liquids (and gases) due to a
pressure difference.
\Define the term antigen - ANS-An antigen is a molecule (usually protein) that stimulates an
immune response resulting in the production of specific antibodies.
\Describe a chemical test you could carry out to show that a piece of coconut contains lipids.
[3] - ANS-(Crush in) ethanol / alcohol; Add (to) water (Order of adding is critical for this
point); Emulsion / white colour
\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 - ANS-1.Permeable
capillary wall/membrane;2. Single cell thick/thin walls, reduces diffusion distance;3.
Flattened (endothelial) cells, reduces diffusion distance;4. Fenestrations, allows some larger
molecules through; 5. Small diameter/ narrow, gives a large surface area to volume/ short
diffusion distance;6. Narrow lumen, reduces flow rate giving more time for diffusion;7. Red
blood cells in contact with wall/ pass in single file, gives short diffusion distance / more time
for diffusion;
\Describe and explain how an increase in temperature affects the rate of an enzyme
controlled reaction. [5] - ANS-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/
\Describe and explain how cell fractionation and ultracentrifugation can be used to isolate
mitochondria from a suspension of animal cells. [5] - ANS-Cell homogenisation to break
open cells; 1. Accept suitable method of breaking open cells. Filter to remove (large) debris /
whole cells; 2. Reject removes cell walls. 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.
\Describe and explain how the lungs are adapted to allow rapid exchange of oxygen
between air in the alveoli and blood in the capillaries around them. (5 marks) - ANS-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;
\Describe and explain the mechanism that causes forced expiration. (4 marks) - ANS-1.
Contraction of internal intercostal muscles 2. Relaxation of diaphragm muscles/Relaxation of
external intercostal muscles; 3. Causes decrease in volume of chest/thoracic cavity; 4. Air
pushed down pressure gradient;
\Describe and explain the role active transport in the absorption of digested food by the
ileum.(4/6 marks) - ANS-1. movement against concentration gradient;2. energy / ATP
required;3. reference to carrier proteins;4. monosaccharides or named / amino acids moved
into epithelial cells;5. reference to co-diffusion e.g. glucose and NaCl;6. monosaccharides or
named / amino acids move into blood
\Describe and explain the role of diffusion in the absorption of digested food by the ileum. (4
marks) - ANS-1. movement along / down concentration gradient;2. monoglycerides /
micelles/fatty acids move into epithelial cells;3. monoglycerides move from epithelium into
blood;4. chylomicrons move into lacteals / lymph;
\Describe and explain the role of facilitated diffusion in the absorption of digested food by the
ileum. (3 marks) - ANS-1. movement along / down concentration gradient;2. reference to
carrier / channel proteins;3. monosaccharides or named / amino acids move into epithelial
cells;
\Describe how a high pressure is produced in the phloem near photosynthesising leaves (3
marks) - ANS-Sucrose AT into sieve tube, water potential becomes lower , water enters
phloem by osmosis from xylem and increased volume increases pressure
\Describe how a microbe can be broken down by the process of Phagocytosis -
ANS-Pathogen is engulfed by the phagocyte. Forming a vesicle surrounding the pathogen
(called a phagosome). Lysosomes fuse with this vesicle releasing digestive enzymes
Lysosome enzymes hydrolyse the proteins and lipids in the pathogen. Waste materials are
ejected from the cell or presented on cell surface memebrane.
\Describe how B-lymphocytes respond when they are stimulated by antigens.(4 marks) -
ANS-divide by mitosis / form clones; produce plasma cells; (plasma cells) make antibodies;
(plasma cells) produce memory cells;
\Describe how farming effects biodiversity of animals (4 marks) - ANS-1. Removal of
plant/weeds/pests; 2. use of pesticides/ploughing2. few(er) habitats / niches;3. (So) lower
diversity of insects / fewer insect species / fewer insect types;3. (So) fewer food sources /
less variety of food.
\Describe how haemoglobin is involved in absorbing oxygen in the lungs and transporting it
to respiring tissues. (6 marks ) - ANS-1. diffusion of oxygen into haemoglobin in red blood
cells; 2. high affinity of haemoglobin in high partial pressure of oxygen 3. loads / becomes
saturated in lungs / at high ppÓ oxygen; 4. oxyhaemoglobin formed; 5. unloads / low affinity
in low partial pressure of oxygen; 6. respiration in tissues gives high CÓ concentration / high
temperature/ high H+ concentration / low pH 7. dissociation curve shifts to right / 8.
oxyhaemoglobin dissociation at higher partial pressure of carbon dioxide.
\Describe how mRNA is produced in the nucleus of a cell. (6 marks) - ANS-1. Helicase; 2.
Breaks hydrogen bonds; 3. Only one DNA strand acts as template; 4. RNA nucleotides
attracted to exposed bases; 5. (Attraction) according to base pairing rule; 6. RNA
polymerase joins (RNA) nucleotides together; 7. Pre-mRNA spliced to remove introns.
