A-LevelBiologyCell structure9700/23 · May/June 2024 · Q114 Marks

The Zika virus is a pathogen that can infect human cells.

(a)Fig. 1.1 is a drawing of the structure of a Zika virus.
(a)(i)In Fig. 1.1, structure A is made of protein. Name structure A.[1]
(a)(ii)In Fig. 1.1, structure B is a single-stranded molecule. Suggest the name of structure B.[1]
(b)Fig. 1.2 is a transmission electron micrograph of human kidney cells infected with Zika viruses. [Figure 1.2]
(b)(i)Calculate the actual diameter of a Zika virus using the line X-Y in Fig. 1.2. Show your working. Give your answer in nanometres (nm).[2]
(b)(ii)A magnification of ×200000 cannot be achieved by a light microscope. The resolution of a transmission electron microscope is also higher than a light microscope. Describe what is meant by the resolution of a microscope.[1]
(c)The vector for Zika virus is the mosquito Aedes aegypti. The mosquito feeds on the blood of an infected person and transmits the virus to another person when it feeds again. Describe the similarities and differences between the transmission of Zika virus disease and the transmission of malaria.[3]
(d)Zika virus vaccines have been developed by scientists. One of the vaccines contains small proteins from the Zika virus.
(d)(i)Explain how giving this vaccine to a person can lead to the development of long-term immunity against Zika virus disease.[4]
(d)(ii)Explain how a vaccination programme may limit the spread of Zika virus disease through a population.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] capsid ; A capsomere A protein coat
[1] RNA / DNA; (actual is RNA) I viral R dsRNA / dsDNA/mRNA/tRNA/rRNA
[2] 50 (nm); A 50/52.5/55/57.5/60 nm
working showing use of correct formula, A = I / M ; length X-Y/÷ magnification
[1] ability to distinguish between two points; AW
[3] malaria is transmitted by Anopheles (rather than Aedes);
plus any two from: max 1 if incorrect context stated for malarial transmission
both are transmitted by vectors ;
both are transmitted by mosquitoes ;
both, are blood-borne diseases / vectors feed on blood;
[4] max three if no correct ref. within response to, memory cells/immunological memory
A T-/B-cells, for, T-/B- lymphocytes
any three from: 1 proteins are, non-self / foreign, antigens ;
2 proteins / antigens, stimulate a primary immune response ;
3 T-lymphocyte / B-lymphocyte, binding / recognition / clonal selection / activation / described in terms of receptor;
4 clonal expansion / cell divides by mitosis to produce a clone / AW ;
5 formation of memory, (T-/B-) lymphocytes ;
mps 3, 4, 5 in context of primary immune response
6,7 further detail;
e.g. (artificial) active immunity
(T-/B-) memory cells, remain in, circulation / the body, for a long time or memory cells are long-lived
(for secondary response) larger numbers of lymphocytes (specific to Zika virus)
greater chance of encountering, Zika virus / pathogen / antigens
secondary immune response is, stronger / faster (than primary immune response)
faster production / higher concentration, of (specific) antibody
(so) person does not have symptoms of disease when infected with (actual) Zika virus
[2] any two from:
ref. to herd immunity;
A a large proportion of the population is immune (to Zika virus disease) ;
detail; e.g. context is less likely/less chance of/less risk of people without immunity / unvaccinated people, less likely / unlikely, to be in contact with an infected person
ora infected person unlikely to be in contact with a non-immune person
idea of increased chance of breaking the transmission cycle
AVP; e.g. can achieve a high percentage cover if Ro high, greater percentage of population need vaccinating ora