AQA A LEVEL BIOLOGY PAPER 2
7402-2 MARK SCHEME MS
CERTIFICATION SCRIPT 2026
QUESTIONS WITH SOLUTIONS
GRADED A+
◍ Describe one way in which the structure of the DNA of a gene may be
changed as a result of a mutation.
Answer: - deletion/ substitution/ addition - of nucleotide / base
◍ Water removed from the reactants joining two molecules together forming a
chemical bond.
Answer: Condensation
◍ The addition of water to the reactants to break a chemical bond between 2
molecules.
Answer: Hydrolysis
◍ 1. Add Benedict's reagent. 2. Heat the solution in a water bath for 5 minutes
at 95 degrees Celsius. 3. Change from blue to brick red as CuO formed.
Answer: Test for Reducing Sugars (3)
◍ Smaller units from which larger molecules are made.
Answer: Monomer
◍ Example of mutagens.
Answer: - high energy ionised particles/ x-rays/ UV- tobacco tar - mustard
gas - chemical mutagen - high energy radiation - gamma rays
◍ Explain how exposure to a mutagenic agent may result in an inactive
enzyme being produced by a cell.
, Answer: - change in sequence of nucleotides - changes sequence of amino
acidsdifferent tertiary structure - inactive enzyme if shape of active site is
changed - ESC'S don't form
◍ 1. Add 2cm³ of food sample then add 2cm³ of dilute HCl and heat.2. Add
2cm³ of NaHCO3 then do test for reducing sugars..
Answer: Non-Reducing Sugars (2)
◍ Add drops of iodine to starch solution. Colour change to blue-black.
Answer: Test for Starch (1)
◍ 1. Mix Test solution with ethanol. 2. Shake for 1 minute then add water. 3.
Cloudy white emulsion.
Answer: Test for Lipids (3)
◍ 1. Obtain equal volumes of test solution and NaOH then add a few drops of
biuret solution (dilute copper (II) sulphate solution). 2. Colour change to
mauve/purple.
Answer: Test for Proteins (2)
◍ 1. Very high resolution. 2. Needs thin and dead specimen. 3. Artefacts can
occur (remnant left on object during prep, such as air bubbles)4. Uses
magnets to focus on specimen5. Uses electrons fired at sample.6. Is not in
colour.
Answer: Transmission Electron Microscope (5)
◍ 1. Inhibitor is similar in shape to substrate so it impermanently binds to the
active site. 2. Prevents ESC from forming, slowing rate.
Answer: Competitive inhibition (2)
◍ Explain how the mutation of a gene can result in an organism lacking a
particular enzyme.
Answer: - mutation changes sequence of nucleotide bases and therefore the
amino acid sequence. - frame shift - incorrect codons- incorrect amino acids
brought to ribosome - tertiary structure changes - non-functional protein
◍ Effect of deletion of a base?.
, Answer: - frame shift- changes sequence of amino acids- substitution alters
one codon - no effect if new triplet codes for same amino acid= degenerate
nature of genetic code
◍ Describe a plasmid.
Answer: - circular dna - contains only a few genes - separate from main
bacterial DNA
◍ Explain the function of a vector.
Answer: - transfers foreign dna/gene into bacteria/ host cell
◍ 1. Molecule will bind to allosteric site. 2. Binding causes a change in active
site. 3. Permanently preventing further ES
C. .
Answer: Non-competitive inhibition (3)
◍ Use your knowledge of monoclonal antibodies to suggest how this antibody
stops the growth of a tumour..
Answer: - antibody has specific tertiary structure - complementary shape to
receptor protein - mutation in intron
◍ Name two structures in a eukaryotic cell that cannot be identified using an
optical microscope.
Answer: - mitochrondrian - ribosome
◍ Describe how the RER is involved in the production of enzymes..
Answer: - ribosomes - to synthesise proteins
◍ 1. DNA helicase breaks the hydrogen bonds between the base pairs 2. 2
single strands formed as the double helix "unzips". 3. Free DNA nucleotides
in the nucleoplasm bond to the complementary bases on the strand. 4. DNA
polymerase forms phosphodiester bonds between adjacent DNA nucleotides
via condensation reaction with the hydrolysis of ATP, forming the
phosphate backbone.
Answer: DNA Replication: Semiconservative (4)
◍ 1. ATP stores or releases only a small amount of energy at a time, so no
, energy is wasted as heat.2. Small and soluble so easily transported3. Easily
broken down, so energy is released instantaneously4. Can be quickly
re-made5. Can make other molecules more reactive via phosphorylation6.
ATP can't pass out of cell, so the cell always has an immediate supply of
energy..
Answer: Describe 6 properties of ATP that make it a good energy source.
(6)
◍ Prevents the cell from drying out. Allows bacteria to stick to each other.
Answer: Slime capsule (2)
◍ Describe how the Golgi apparatus is involved in the secretion of enzymes..
Answer: - modifies proteins
◍ Used for attachment of a cell to a surface.
Answer: Fimbria
◍ purpose of: No air-sealing grease was applied to either surface of the leaf..
Answer: - means stomata open which allows normal c02 uptake
◍ purpose: The lower surface of the leaf was covered in air-sealing grease
thatprevents gas exchange..
Answer: - grease stops c02 uptake through stomata
◍ Involved in bacterial conjugation.
Answer: Pilli
◍ purpose: Both the lower surface and the upper surface of the leaf were
covered in air-sealing grease that prevents gas exchange..
Answer: - stops all co2 uptake - shows sealing is effective
◍ The stomata close when the light is turned off.Explain the advantage of this
to the plant..
Answer: - because water is lost through the stomata - closure prevents/
reduces water loss and decreases the wp gradient- maintains the water
content of cells
◍ Invagination of cell membrane. Site of cell respiration (prokaryotes).
7402-2 MARK SCHEME MS
CERTIFICATION SCRIPT 2026
QUESTIONS WITH SOLUTIONS
GRADED A+
◍ Describe one way in which the structure of the DNA of a gene may be
changed as a result of a mutation.
Answer: - deletion/ substitution/ addition - of nucleotide / base
◍ Water removed from the reactants joining two molecules together forming a
chemical bond.
Answer: Condensation
◍ The addition of water to the reactants to break a chemical bond between 2
molecules.
Answer: Hydrolysis
◍ 1. Add Benedict's reagent. 2. Heat the solution in a water bath for 5 minutes
at 95 degrees Celsius. 3. Change from blue to brick red as CuO formed.
Answer: Test for Reducing Sugars (3)
◍ Smaller units from which larger molecules are made.
Answer: Monomer
◍ Example of mutagens.
Answer: - high energy ionised particles/ x-rays/ UV- tobacco tar - mustard
gas - chemical mutagen - high energy radiation - gamma rays
◍ Explain how exposure to a mutagenic agent may result in an inactive
enzyme being produced by a cell.
, Answer: - change in sequence of nucleotides - changes sequence of amino
acidsdifferent tertiary structure - inactive enzyme if shape of active site is
changed - ESC'S don't form
◍ 1. Add 2cm³ of food sample then add 2cm³ of dilute HCl and heat.2. Add
2cm³ of NaHCO3 then do test for reducing sugars..
Answer: Non-Reducing Sugars (2)
◍ Add drops of iodine to starch solution. Colour change to blue-black.
Answer: Test for Starch (1)
◍ 1. Mix Test solution with ethanol. 2. Shake for 1 minute then add water. 3.
Cloudy white emulsion.
Answer: Test for Lipids (3)
◍ 1. Obtain equal volumes of test solution and NaOH then add a few drops of
biuret solution (dilute copper (II) sulphate solution). 2. Colour change to
mauve/purple.
Answer: Test for Proteins (2)
◍ 1. Very high resolution. 2. Needs thin and dead specimen. 3. Artefacts can
occur (remnant left on object during prep, such as air bubbles)4. Uses
magnets to focus on specimen5. Uses electrons fired at sample.6. Is not in
colour.
Answer: Transmission Electron Microscope (5)
◍ 1. Inhibitor is similar in shape to substrate so it impermanently binds to the
active site. 2. Prevents ESC from forming, slowing rate.
Answer: Competitive inhibition (2)
◍ Explain how the mutation of a gene can result in an organism lacking a
particular enzyme.
Answer: - mutation changes sequence of nucleotide bases and therefore the
amino acid sequence. - frame shift - incorrect codons- incorrect amino acids
brought to ribosome - tertiary structure changes - non-functional protein
◍ Effect of deletion of a base?.
, Answer: - frame shift- changes sequence of amino acids- substitution alters
one codon - no effect if new triplet codes for same amino acid= degenerate
nature of genetic code
◍ Describe a plasmid.
Answer: - circular dna - contains only a few genes - separate from main
bacterial DNA
◍ Explain the function of a vector.
Answer: - transfers foreign dna/gene into bacteria/ host cell
◍ 1. Molecule will bind to allosteric site. 2. Binding causes a change in active
site. 3. Permanently preventing further ES
C. .
Answer: Non-competitive inhibition (3)
◍ Use your knowledge of monoclonal antibodies to suggest how this antibody
stops the growth of a tumour..
Answer: - antibody has specific tertiary structure - complementary shape to
receptor protein - mutation in intron
◍ Name two structures in a eukaryotic cell that cannot be identified using an
optical microscope.
Answer: - mitochrondrian - ribosome
◍ Describe how the RER is involved in the production of enzymes..
Answer: - ribosomes - to synthesise proteins
◍ 1. DNA helicase breaks the hydrogen bonds between the base pairs 2. 2
single strands formed as the double helix "unzips". 3. Free DNA nucleotides
in the nucleoplasm bond to the complementary bases on the strand. 4. DNA
polymerase forms phosphodiester bonds between adjacent DNA nucleotides
via condensation reaction with the hydrolysis of ATP, forming the
phosphate backbone.
Answer: DNA Replication: Semiconservative (4)
◍ 1. ATP stores or releases only a small amount of energy at a time, so no
, energy is wasted as heat.2. Small and soluble so easily transported3. Easily
broken down, so energy is released instantaneously4. Can be quickly
re-made5. Can make other molecules more reactive via phosphorylation6.
ATP can't pass out of cell, so the cell always has an immediate supply of
energy..
Answer: Describe 6 properties of ATP that make it a good energy source.
(6)
◍ Prevents the cell from drying out. Allows bacteria to stick to each other.
Answer: Slime capsule (2)
◍ Describe how the Golgi apparatus is involved in the secretion of enzymes..
Answer: - modifies proteins
◍ Used for attachment of a cell to a surface.
Answer: Fimbria
◍ purpose of: No air-sealing grease was applied to either surface of the leaf..
Answer: - means stomata open which allows normal c02 uptake
◍ purpose: The lower surface of the leaf was covered in air-sealing grease
thatprevents gas exchange..
Answer: - grease stops c02 uptake through stomata
◍ Involved in bacterial conjugation.
Answer: Pilli
◍ purpose: Both the lower surface and the upper surface of the leaf were
covered in air-sealing grease that prevents gas exchange..
Answer: - stops all co2 uptake - shows sealing is effective
◍ The stomata close when the light is turned off.Explain the advantage of this
to the plant..
Answer: - because water is lost through the stomata - closure prevents/
reduces water loss and decreases the wp gradient- maintains the water
content of cells
◍ Invagination of cell membrane. Site of cell respiration (prokaryotes).
