9700 Biology November 2025 Question Paper 23

1 Many substances can move through cell surface membranes between the cytoplasm of animal cells and the extracellular environment.

(a) A student made a drawing to summarise the movement of substances across the cell surface membranes of mammalian red blood cells.

Fig. 1.1 shows the drawing made by the student: • Each arrow indicates the movement of a substance through the membrane. • The number of each of the 4 shapes represents the relative concentrations of each substance in the cytoplasm and in the blood plasma. A B ATP ADP + Pi cytoplasm of red blood cell blood plasma C D Fig. 1.1

The student carried out research and made a list of some of the substances found in red blood cells as shown in Fig. 1.2. sodium ions oxygen haemoglobin carbon dioxide potassium ions calcium ions chloride ions carbonic anhydrase hydrogencarbonate ions glucose amino acids Fig. 1.2 , ,

Table 1.1 shows information about the 4 types of movement of substances across the cell surface membranes of red blood cells as shown in Fig. 1.1.

Complete Table 1.1 using the information in Fig. 1.1 and Fig. 1.2. Table 1.1 letter from Fig. 1.1 type of movement name of part of membrane involved example of a substance that moves across the membrane (from Fig. 1.2) A simple diffusion phospholipids B facilitated diffusion calcium ions C facilitated diffusion D

[5]

(b) Some viruses infect plants through the surfaces of damaged leaves. These plant viruses can travel from one leaf cell to another without having to pass through any cell surface membranes.

Explain how some plant viruses can travel from one cell to another without passing through cell surface membranes [2]

[Total: 7] , ,

2 Collagen is a fibrous protein found in many tissues in animals. Fig. 2.1 shows the composition of a collagen fibre. 5μm 50nm 1.5nm collagen fibre

• a bundle of collagen fibrils collagen fibril collagen molecule 3 polypeptides 300nm Fig. 2.1

(a) (i) Describe the arrangement of the 3 polypeptides in each molecule of collagen [2]

(ii) With reference to Fig. 2.1, explain how the molecules of collagen are arranged and held together in a collagen fibril [3] , ,

(b) Collagen fibres and elastic fibres are found in the structures of the gas exchange system of mammals.

(i) Suggest two properties of collagen that contribute to the function of cartilage in the trachea in the gas exchange system [2]

(ii) State the function of elastic fibres in the alveoli in the lungs [1] , ,

(c) Table 2.1 shows the DNA triplets in the two strands of DNA in part of a gene that codes for one of the polypeptides in collagen. Table 2.1 non- transcribed strand GGT CCA ATG GGT CCC CGA GGT CCC CCA GGT template strand CCA GGT TAC CCA GGG GCT CCA GGG GGT CCA amino acid gly

Table 2.2 shows the triplets of bases in DNA and the amino acids for which they code.

The table can be used to determine the sequence of the amino acids in a polypeptide. Table 2.2 second base first base third base T T TTT phe ser pro thr ala leu tyr cys stop trp arg ser arg gly stop his gln asn lys asp glu leu ile met val TTC TTA TTG C CTT CTC CTA CTG C TCT TCC TCA TCG A ATT ATC ATA ATG ACT ACC ACA ACG G GTT GTC GTA GTG GCT GCC GCA GCG CCT CCC CCA CCG A TAT TAC TAA TAG CAT CAC CAA CAG G TGT TGC TGA TGG CGT CGC CGA CGG AAT AAC AAA AAG AGT AGC AGA AGG GAT GAC GAA GAG GGT GGC GGA GGG T C A G T C A G T C A G T C A G

(i) Complete Table 2.1 to show the amino acids coded by the DNA nucleotide sequence in Table 2.1. [1] , ,

(ii) The sequence of amino acids that you have worked out is representative of the whole of the collagen polypeptide.

Explain how the sequence of amino acids makes the polypeptide suitable as a component of a collagen molecule [3]

(iii) Two mutations, P and Q, can have an effect on the primary structure of the polypeptide. • Mutation P is a deletion of the first nucleotide pair in the DNA nucleotide sequence shown in Table 2.1. • Mutation Q is a substitution of G with T as the first base in the DNA nucleotide sequence shown in Table 2.1.

State the effects of the mutations, P and Q, on the primary structure of the polypeptide. mutation P mutation Q [2]

[Total: 14] , ,

3 (a) Describe the induced-fit hypothesis of enzyme action [3]

(b) Many marine organisms can become attached to hard surfaces such as rocks or the surfaces of ships. These organisms are known as fouling organisms.

The larva of the acorn barnacle, Amphibalanus amphitrite, is an example of a fouling organism. One of these barnacle larvae is shown in Fig. 3.1. magnification ×160 Fig. 3.1

The larvae of A. amphitrite use a protein to attach themselves to the surfaces of ships.

It is expensive to remove fouling organisms from ships. Scientists have developed substances to prevent the attachment of larvae. However, some of these substances are toxic and have been responsible for a decrease in marine biodiversity.

Scientists investigated the effect of using an immobilised protease, subtilisin A, to prevent the attachment of the larvae of A. amphitrite to surfaces.

The scientists used 4 different concentrations of subtilisin A which had been immobilised onto the surface of a polymer film. As a control they used denatured subtilisin A immobilised onto the surface of the same polymer. Glass slides were also used as a control. , ,

The larvae were released into 6 tanks of artificial sea water: • 4 tanks, each with a polymer surface and a different concentration of immobilised subtilisin A • 1 tank with a polymer surface and denatured immobilised subtilisin A • 1 tank with glass slides instead of a polymer surface.

The number of larvae that attached to the different surfaces in the tanks was counted after 24 hours and again after 48 hours.

The number of larvae attached in each tank was expressed as the percentage of the total number of larvae released in each tank. The results are shown in Fig. 3.2. 0 1 2 3 4 10 20 30 40 50 percentage of larvae attached to surfaces polymer surface with denatured immobilised subtilisin A polymer surface with immobilised subtilisin A of increasing concentration glass slides (no polymer) 60 70 Key after 24 hours after 48 hours Fig. 3.2

(i) With reference to the data in Fig. 3.2, discuss whether subtilisin A is effective in preventing the attachment of the larvae [4] , ,

(ii) The scientists extended their investigation by applying the polymer with immobilised subtilisin A to the outside of the bottom of small ships.

Two factors that need to be taken into consideration in this type of investigation are the temperature and pH of the sea water.

Outline two other factors that need to be taken into consideration when investigating the suitability of immobilised subtilisin A as an anti-fouling agent for ships [2]

[Total: 9] , , Question 4 starts on page 12. , ,

4 (a) Fig. 4.1 shows a phosphorylated nucleotide which is one of the monomers that is used to synthesise DNA during replication. O CH2 NH2 N N O OH H P O P O P O –O O O O– O– O– N N adenine Fig. 4.1

(i) State the meaning of monomers of DNA [1]

(ii) State how ATP differs in structure from the phosphorylated nucleotide shown in Fig. 4.1 [1]

(iii) State the process occurring in all cells that results in the production of ATP [1] , ,

(b) Fig. 4.2 shows a short length of a DNA molecule. One of the strands of the DNA molecule is labelled Y. N O O CH3 CH2 CH2 CH2 3ʹ 5ʹ 5ʹ O O N O O P O –O P O H H H H H O –O O P O 3ʹ O O– O P O O O– N N O O N H H N N N N O CH2 O N N H O N N N N X Y Fig. 4.2

(i) Complete Fig. 4.2 by drawing dotted lines to represent all the hydrogen bonds between the two strands of the DNA molecule. [2]

(ii) State the name of the bond X [1]

[Total: 6] , ,

5 Inhibitors are substances that prevent biological processes in a variety of different ways.

Table 5.1 shows some antibiotics, their modes of action and the diseases which they are used to treat. Table 5.1 antibiotic mode of action disease erythromycin binds to ribosomes to inhibit translation cholera penicillin enzyme inhibitor tetanus rifampicin inhibits the function of RNA polymerase in transcription tuberculosis

(a) Suggest why erythromycin can inhibit translation in the bacterium that causes cholera and not inhibit translation in humans who are infected with this pathogen [2]

(b) State why penicillin does not act on human cells [1]

(c) Explain one way in which rifampicin may inhibit the action of RNA polymerase in transcription [1]

[Total: 4] , ,

6 (a) A student studied the structure of a mammalian heart.

The student took a photograph of the left side of a dissected heart as shown in Fig. 6.1. Fig. 6.1

Identify two features of the left side of the heart visible in Fig. 6.1 and explain how each feature is adapted to the function of the heart. feature explanation feature explanation [4] , ,

(b) Cardiac muscle is described as myogenic. This means the electrical activity controlling the rhythm of a regular heartbeat begins within the muscle tissue of the heart.

Describe how electrical activity within the heart controls each heartbeat [4]

(c) Tissue fluid is formed from blood plasma as it flows through capillaries.

Fig. 6.2 is a diagram of a capillary and some adjacent tissue cells in a capillary network. Fig. 6.2

(i) Describe two functions of tissue fluid [2] , ,

(ii) With reference to Fig. 6.2, describe how tissue fluid is formed [3]

(d) Measles is a common disease caused by a virus. Vaccination to prevent the disease has been very successful.

(i) A child receives a vaccine for measles.

Explain why only some of the T-lymphocytes in the child respond to the measles vaccine [2]

(ii) Describe the events that occur in an immune response to a vaccine that result in lymphocytes that provide long-term immunity to measles [5] [Total: 20] , ,