AS Biology Exam Style questions and answers 2023 with
complete solution
When HIV infects a human cell, the following events occur.
-A single-stranded length of HIV DNA is made
-The human cell then makes a complementary strand to the HIV DNA
The complementary strand is made in the same way as a new complementary
strand is made during semi-conservative replication of human DNA
Describe how the complementary strand of HIV DNA is made. [3 marks]
-complementary nucleotides/ base pairs
-DNA polymerase
-nucleotides join together to form new strand/ phosphodiester bonds form
Constrast the structures of DNA and mRNA molecules to give three differences.
[3 marks]
1. DNA has a deoxybraiose sugar whereas mRNA has a ribose sugar
2. DNA is double stranded whereas mRNA is single-stranded
3. DNA is a long molecule whereas mRNA is smaller
-thymine in DNA and uracil in RNA
-DNA has base pairing and mRNA doesn't
-DNA has hydrogen bonding and mRNA doesn't
-DNA has introns/ non-coding sequences and mRNA doesn't
Describe the difference between the structure of a triglyceride molecule and the
structure of a phospholipid molecule [1 mark]
a fatty acid is replaced by a phosphate group
Describe how you would test for the presence of a lipid in sample of food [2
marks]
add ethanol, then add water
white emulsion shows lipid
Describe how a saturated fatty acid is different from an unsaturated fatty acid [1
mark]
saturated has no double bonds between carbons
A fat substitute cannot be digested in the gut by lipase. Suggest why. [2 marks]
fat substitute is not complementary
unable to bind to active site of lipase
Cells constantly hydrolyse ATP to provide energy.
Describe how ATP is resynthesised in cells. [2 marks]
, From ADP and phosphate;
2. By ATP synthase;
3. During respiration/photosynthesis;
Give two ways in which the hydrolysis of ATP is used in cells. [2 marks]
1. To provide energy for other reactions/named process;
2. To add phosphate to other substances and make them more reactive/change their
shape;
Describe the induced-fit model of enzyme action [2 marks]
1. (before reaction) active site not complementary to/does not fit substrate;
2. Shape of active site changes as substrate binds/as enzyme- substrate complex
forms;
3. Stressing/distorting/bending bonds (in substrate leading to reaction);
Human papilloma virus (HPV) is the main cause of cervial cancer. A vaccine has
been developed to protect girls and women from HPV. Describe how giving this
vaccine leads to production of antibody against HPV. [4 marks]
1. Vaccine/it contains antigen (from HPV);
2. Displayed on antigen-presenting cells;
3. Specific helper T cell (detects antigen and) stimulates specific B cell;
4. B cell divides/goes through mitosis/forms clone to give plasma cells;
5. B cell/plasma cell produces antibody;
The doctors carried out a statistical test to determine whether the antibody
concentrations were significantly different in girls given two doses of the vaccine,
compared with those given three doses. They determined the mean
concentrations of antibody 9 months after the first does of vaccine
What statistical test should the doctors have used? Give the reason for your
answer [1 mark]
t-test, because comparing two means
There is genetic diversity within HPV.
Give two ways doctors could use base sequences to compare different types of
HPV. [2 marks]
1. Compare (base sequences of) DNA;
2. Look for mutations/named mutations (that change the base sequence);
3. Compare (base sequences of) (m)RNA;
Endopeptidases and exopeptidases are involved in the hydrolysis of proteins.
Name the other type of enzyme required for the complete hydrolysis of proteins
to amino acids. [1 marks]
dipeptidases
Suggest and explain why the combined actions of endopeptidases and
exopeptidases are more efficient than exopeptidases on their own [ 2marks]
1. Endopeptidases hydrolyse internal (peptide bonds)
OR
Exopeptidases remove amino acids/hydrolyse (bonds) at end(s);
2. More ends or increase in surface area (for exopeptidases);
complete solution
When HIV infects a human cell, the following events occur.
-A single-stranded length of HIV DNA is made
-The human cell then makes a complementary strand to the HIV DNA
The complementary strand is made in the same way as a new complementary
strand is made during semi-conservative replication of human DNA
Describe how the complementary strand of HIV DNA is made. [3 marks]
-complementary nucleotides/ base pairs
-DNA polymerase
-nucleotides join together to form new strand/ phosphodiester bonds form
Constrast the structures of DNA and mRNA molecules to give three differences.
[3 marks]
1. DNA has a deoxybraiose sugar whereas mRNA has a ribose sugar
2. DNA is double stranded whereas mRNA is single-stranded
3. DNA is a long molecule whereas mRNA is smaller
-thymine in DNA and uracil in RNA
-DNA has base pairing and mRNA doesn't
-DNA has hydrogen bonding and mRNA doesn't
-DNA has introns/ non-coding sequences and mRNA doesn't
Describe the difference between the structure of a triglyceride molecule and the
structure of a phospholipid molecule [1 mark]
a fatty acid is replaced by a phosphate group
Describe how you would test for the presence of a lipid in sample of food [2
marks]
add ethanol, then add water
white emulsion shows lipid
Describe how a saturated fatty acid is different from an unsaturated fatty acid [1
mark]
saturated has no double bonds between carbons
A fat substitute cannot be digested in the gut by lipase. Suggest why. [2 marks]
fat substitute is not complementary
unable to bind to active site of lipase
Cells constantly hydrolyse ATP to provide energy.
Describe how ATP is resynthesised in cells. [2 marks]
, From ADP and phosphate;
2. By ATP synthase;
3. During respiration/photosynthesis;
Give two ways in which the hydrolysis of ATP is used in cells. [2 marks]
1. To provide energy for other reactions/named process;
2. To add phosphate to other substances and make them more reactive/change their
shape;
Describe the induced-fit model of enzyme action [2 marks]
1. (before reaction) active site not complementary to/does not fit substrate;
2. Shape of active site changes as substrate binds/as enzyme- substrate complex
forms;
3. Stressing/distorting/bending bonds (in substrate leading to reaction);
Human papilloma virus (HPV) is the main cause of cervial cancer. A vaccine has
been developed to protect girls and women from HPV. Describe how giving this
vaccine leads to production of antibody against HPV. [4 marks]
1. Vaccine/it contains antigen (from HPV);
2. Displayed on antigen-presenting cells;
3. Specific helper T cell (detects antigen and) stimulates specific B cell;
4. B cell divides/goes through mitosis/forms clone to give plasma cells;
5. B cell/plasma cell produces antibody;
The doctors carried out a statistical test to determine whether the antibody
concentrations were significantly different in girls given two doses of the vaccine,
compared with those given three doses. They determined the mean
concentrations of antibody 9 months after the first does of vaccine
What statistical test should the doctors have used? Give the reason for your
answer [1 mark]
t-test, because comparing two means
There is genetic diversity within HPV.
Give two ways doctors could use base sequences to compare different types of
HPV. [2 marks]
1. Compare (base sequences of) DNA;
2. Look for mutations/named mutations (that change the base sequence);
3. Compare (base sequences of) (m)RNA;
Endopeptidases and exopeptidases are involved in the hydrolysis of proteins.
Name the other type of enzyme required for the complete hydrolysis of proteins
to amino acids. [1 marks]
dipeptidases
Suggest and explain why the combined actions of endopeptidases and
exopeptidases are more efficient than exopeptidases on their own [ 2marks]
1. Endopeptidases hydrolyse internal (peptide bonds)
OR
Exopeptidases remove amino acids/hydrolyse (bonds) at end(s);
2. More ends or increase in surface area (for exopeptidases);
