AQA AS LEVEL BIOLOGY
PAPER 2 MAY 2025
QUESTION PAPER
1. Explain how the structure of a phospholipid molecule makes it suitable
for forming membranes.
Answer:
Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails. This
causes them to arrange into a bilayer in aqueous environments, with heads facing outwards and
tails facing inwards, forming a selectively permeable membrane.
2. Describe the role of enzymes in the digestion of proteins.
Answer:
Proteases break down proteins into peptides and then into amino acids by hydrolyzing peptide
bonds. This allows absorption in the small intestine.
3. What is meant by the term ‘active transport’? How is it different from
facilitated diffusion?
Answer:
Active transport moves substances against their concentration gradient using ATP and carrier
proteins. Facilitated diffusion also uses carrier proteins but moves substances down their
concentration gradient and does not require ATP.
4. Describe how the structure of DNA enables it to replicate accurately.
Answer:
DNA has complementary base pairing (A with T, G with C), allowing each strand to serve as a
,template. Hydrogen bonds between bases are weak and allow strand separation, while the
sequence of bases ensures accurate replication by DNA polymerase.
5. Explain the effect of a mutation in a gene on the protein produced.
Answer:
A mutation may change the DNA base sequence, leading to a different mRNA codon. This
could change an amino acid in the polypeptide, possibly altering protein structure and function.
Some mutations are silent and have no effect.
6. Describe the role of mRNA in protein synthesis.
Answer:
mRNA carries the genetic code from DNA in the nucleus to ribosomes in the cytoplasm, where
it is translated into a polypeptide chain.
7. Explain how water moves from the roots to the leaves in the xylem.
Answer:
Water moves via transpiration pull, cohesion between water molecules, and adhesion to xylem
walls. Evaporation from leaves creates a negative pressure that draws water up the plant.
8. Compare and contrast the structure of prokaryotic and eukaryotic cells.
Answer:
Both have a plasma membrane and ribosomes. Prokaryotes lack membrane-bound organelles
and a nucleus, while eukaryotes have both. Prokaryotes often have circular DNA, eukaryotes
have linear DNA in the nucleus.
9. Explain how antibodies destroy pathogens.
Answer:
Antibodies bind to antigens on pathogens, neutralizing them and marking them for
phagocytosis. Some antibodies cause agglutination, making it easier for phagocytes to engulf
pathogens.
10. What is the role of the diaphragm in ventilation?
, Answer:
During inhalation, the diaphragm contracts and flattens, increasing thoracic volume and
reducing pressure, drawing air into the lungs. During exhalation, it relaxes and domes upward,
decreasing volume and increasing pressure to expel air.
11. What is the function of the Golgi apparatus in a cell?
Answer:
The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or use
within the cell. It also forms lysosomes.
12. Explain the role of ATP in cells.
Answer:
ATP provides energy for cellular processes by releasing energy when its high-energy
phosphate bonds are broken through hydrolysis.
13. What is a monosaccharide? Give two examples.
Answer:
A monosaccharide is the simplest form of carbohydrate; examples include glucose and
fructose.
14. How does temperature affect enzyme activity?
Answer:
As temperature increases, enzyme activity rises due to more kinetic energy until an optimum is
reached. Beyond this, enzymes denature, and activity declines.
15. Describe the structure and function of ribosomes.
Answer:
Ribosomes are made of rRNA and proteins. They are the site of protein synthesis, translating
mRNA into amino acid chains.
16. What is osmosis?
PAPER 2 MAY 2025
QUESTION PAPER
1. Explain how the structure of a phospholipid molecule makes it suitable
for forming membranes.
Answer:
Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails. This
causes them to arrange into a bilayer in aqueous environments, with heads facing outwards and
tails facing inwards, forming a selectively permeable membrane.
2. Describe the role of enzymes in the digestion of proteins.
Answer:
Proteases break down proteins into peptides and then into amino acids by hydrolyzing peptide
bonds. This allows absorption in the small intestine.
3. What is meant by the term ‘active transport’? How is it different from
facilitated diffusion?
Answer:
Active transport moves substances against their concentration gradient using ATP and carrier
proteins. Facilitated diffusion also uses carrier proteins but moves substances down their
concentration gradient and does not require ATP.
4. Describe how the structure of DNA enables it to replicate accurately.
Answer:
DNA has complementary base pairing (A with T, G with C), allowing each strand to serve as a
,template. Hydrogen bonds between bases are weak and allow strand separation, while the
sequence of bases ensures accurate replication by DNA polymerase.
5. Explain the effect of a mutation in a gene on the protein produced.
Answer:
A mutation may change the DNA base sequence, leading to a different mRNA codon. This
could change an amino acid in the polypeptide, possibly altering protein structure and function.
Some mutations are silent and have no effect.
6. Describe the role of mRNA in protein synthesis.
Answer:
mRNA carries the genetic code from DNA in the nucleus to ribosomes in the cytoplasm, where
it is translated into a polypeptide chain.
7. Explain how water moves from the roots to the leaves in the xylem.
Answer:
Water moves via transpiration pull, cohesion between water molecules, and adhesion to xylem
walls. Evaporation from leaves creates a negative pressure that draws water up the plant.
8. Compare and contrast the structure of prokaryotic and eukaryotic cells.
Answer:
Both have a plasma membrane and ribosomes. Prokaryotes lack membrane-bound organelles
and a nucleus, while eukaryotes have both. Prokaryotes often have circular DNA, eukaryotes
have linear DNA in the nucleus.
9. Explain how antibodies destroy pathogens.
Answer:
Antibodies bind to antigens on pathogens, neutralizing them and marking them for
phagocytosis. Some antibodies cause agglutination, making it easier for phagocytes to engulf
pathogens.
10. What is the role of the diaphragm in ventilation?
, Answer:
During inhalation, the diaphragm contracts and flattens, increasing thoracic volume and
reducing pressure, drawing air into the lungs. During exhalation, it relaxes and domes upward,
decreasing volume and increasing pressure to expel air.
11. What is the function of the Golgi apparatus in a cell?
Answer:
The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or use
within the cell. It also forms lysosomes.
12. Explain the role of ATP in cells.
Answer:
ATP provides energy for cellular processes by releasing energy when its high-energy
phosphate bonds are broken through hydrolysis.
13. What is a monosaccharide? Give two examples.
Answer:
A monosaccharide is the simplest form of carbohydrate; examples include glucose and
fructose.
14. How does temperature affect enzyme activity?
Answer:
As temperature increases, enzyme activity rises due to more kinetic energy until an optimum is
reached. Beyond this, enzymes denature, and activity declines.
15. Describe the structure and function of ribosomes.
Answer:
Ribosomes are made of rRNA and proteins. They are the site of protein synthesis, translating
mRNA into amino acid chains.
16. What is osmosis?
