AQA BIOLOGY PAPER 3 ACTUAL PRACTICE EXAM
WITH WELL ELABORATED AND MOST TESTED REAL
PRACTICE QUESTIONS AND 100% CORRECT
VERIFIED ANSWERS WITH DETAILED RATIONALES
PLUS EXPERT ANSWER KEY 2026-2027 Q&A 100%
GUARANTEED PASS A+ INSTANT DOWNLOAD PDF
1. Which of the following is a monomer used to build polysaccharides?
A) Amino acid
B) Nucleotide
C) Monosaccharide
D) Fatty acid
Monosaccharides such as glucose are the monomers that polymerise to
form polysaccharides like starch and glycogen.
2. The disaccharide lactose is composed of:
A) Glucose + glucose
B) Glucose + galactose
C) Glucose + fructose
D) Fructose + galactose
Lactose is a disaccharide formed from a glucose molecule and a galactose
molecule.
3. Which level of protein structure is stabilised by hydrogen bonds between the
carbonyl group of one amino acid and the amine group of another in the
same chain?
A) Primary
B) Secondary
C) Tertiary
D) Quaternary
, Secondary structure (alpha helices and beta-pleated sheets) is stabilised by
hydrogen bonds between backbone atoms (C=O of one residue and N-H of
another).
4. A hydrolysis reaction using water breaks which type of bond between two
monosaccharides?
A) Peptide bond
B) Ester bond
C) Glycosidic bond
D) Phosphodiester bond
Hydrolysis uses water to break the glycosidic bond between
monosaccharides.
5. Which property of water makes it an excellent solvent for metabolic
reactions?
A) High specific heat capacity
B) Polarity
C) Low density as a solid
D) High surface tension
Water is dipolar, with slightly positive hydrogen atoms and a slightly
negative oxygen atom, allowing it to dissolve ionic and polar substances.
6. In a DNA nucleotide, the phosphate group is attached to which carbon of the
pentose sugar?
A) 1'
B) 2'
C) 5'
D) 3'
The phosphate group is attached to the 5' carbon of the deoxyribose sugar
in a nucleotide.
7. Which of the following is NOT a difference between DNA and RNA?
A) RNA has uracil instead of thymine
B) RNA is single-stranded
C) RNA contains a ribose sugar
D) RNA is always found in the nucleus
Both DNA and RNA contain a pentose sugar; DNA contains deoxyribose
, while RNA contains ribose. This is a difference. However, RNA is not
always found in the nucleus; it is also found in the cytoplasm.
8. The semi-conservative model of DNA replication was proven by:
A) Meselson and Stahl
B) Watson and Crick
C) Hershey and Chase
D) Griffith
Meselson and Stahl used nitrogen isotopes to demonstrate that DNA
replication is semi-conservative.
9. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A) DNA polymerase
B) DNA helicase
C) DNA ligase
D) RNA polymerase
DNA helicase breaks the hydrogen bonds between complementary base
pairs, unwinding the double helix.
10.During translation, the ribosome moves along the mRNA in which direction?
A) 3' to 5'
B) 5' to 3'
C) Randomly
D) Both directions
The ribosome reads the mRNA codons from the 5' end to the 3' end.
11.Which of the following is a stop codon?
A) AUG
B) UAA
C) UAC
D) GUA
UAA, UAG and UGA are stop codons that do not code for an amino acid.
12.In prokaryotic cells, DNA is:
A) Linear and associated with histones
B) Circular and not associated with histones
WITH WELL ELABORATED AND MOST TESTED REAL
PRACTICE QUESTIONS AND 100% CORRECT
VERIFIED ANSWERS WITH DETAILED RATIONALES
PLUS EXPERT ANSWER KEY 2026-2027 Q&A 100%
GUARANTEED PASS A+ INSTANT DOWNLOAD PDF
1. Which of the following is a monomer used to build polysaccharides?
A) Amino acid
B) Nucleotide
C) Monosaccharide
D) Fatty acid
Monosaccharides such as glucose are the monomers that polymerise to
form polysaccharides like starch and glycogen.
2. The disaccharide lactose is composed of:
A) Glucose + glucose
B) Glucose + galactose
C) Glucose + fructose
D) Fructose + galactose
Lactose is a disaccharide formed from a glucose molecule and a galactose
molecule.
3. Which level of protein structure is stabilised by hydrogen bonds between the
carbonyl group of one amino acid and the amine group of another in the
same chain?
A) Primary
B) Secondary
C) Tertiary
D) Quaternary
, Secondary structure (alpha helices and beta-pleated sheets) is stabilised by
hydrogen bonds between backbone atoms (C=O of one residue and N-H of
another).
4. A hydrolysis reaction using water breaks which type of bond between two
monosaccharides?
A) Peptide bond
B) Ester bond
C) Glycosidic bond
D) Phosphodiester bond
Hydrolysis uses water to break the glycosidic bond between
monosaccharides.
5. Which property of water makes it an excellent solvent for metabolic
reactions?
A) High specific heat capacity
B) Polarity
C) Low density as a solid
D) High surface tension
Water is dipolar, with slightly positive hydrogen atoms and a slightly
negative oxygen atom, allowing it to dissolve ionic and polar substances.
6. In a DNA nucleotide, the phosphate group is attached to which carbon of the
pentose sugar?
A) 1'
B) 2'
C) 5'
D) 3'
The phosphate group is attached to the 5' carbon of the deoxyribose sugar
in a nucleotide.
7. Which of the following is NOT a difference between DNA and RNA?
A) RNA has uracil instead of thymine
B) RNA is single-stranded
C) RNA contains a ribose sugar
D) RNA is always found in the nucleus
Both DNA and RNA contain a pentose sugar; DNA contains deoxyribose
, while RNA contains ribose. This is a difference. However, RNA is not
always found in the nucleus; it is also found in the cytoplasm.
8. The semi-conservative model of DNA replication was proven by:
A) Meselson and Stahl
B) Watson and Crick
C) Hershey and Chase
D) Griffith
Meselson and Stahl used nitrogen isotopes to demonstrate that DNA
replication is semi-conservative.
9. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A) DNA polymerase
B) DNA helicase
C) DNA ligase
D) RNA polymerase
DNA helicase breaks the hydrogen bonds between complementary base
pairs, unwinding the double helix.
10.During translation, the ribosome moves along the mRNA in which direction?
A) 3' to 5'
B) 5' to 3'
C) Randomly
D) Both directions
The ribosome reads the mRNA codons from the 5' end to the 3' end.
11.Which of the following is a stop codon?
A) AUG
B) UAA
C) UAC
D) GUA
UAA, UAG and UGA are stop codons that do not code for an amino acid.
12.In prokaryotic cells, DNA is:
A) Linear and associated with histones
B) Circular and not associated with histones
