A-LevelBiologyTransport in mammals9700/21 · Oct/Nov 2022 · Q212 Marks

Fig. 2.1 is a simplified diagram of the human circulatory system. [Figure 2.1]

(a)(i)State why the human circulatory system is described as a closed, double circulation.[2]
(a)(ii)Identify blood vessel Q and blood vessel R, shown in Fig. 2.1. Q R[1]
(a)(iii)Blood leaving the heart passes through valves before it enters blood vessel R. Describe the differences between the structure of blood vessel Q and the structure of blood vessel R. Do not refer to valves in your answer.[3]
(b)(i)State how the quaternary structure of a human antibody molecule differs from the quaternary structure of the shark antibody molecule shown in Fig. 2.2.[1]
(b)(ii)Human antibodies are used in the treatment of some forms of cancer. However, the antibodies injected into the bloodstream can only reach a small percentage of the cancer cells that form the cancerous tumour. Shark antibodies are smaller than human antibodies. Scientists are researching the possibility of injecting shark antibodies into the bloodstream to treat cancerous tumours in humans. Suggest how using the smaller shark antibodies may be more effective in reaching a greater percentage of cancer cells than human antibodies and lead to greater success at treating cancer.[2]
(b)(iii)Antibodies can also be used in the prevention of infectious diseases. Explain how injection of antibodies into the bloodstream can protect a person from disease after infection by a pathogen.[3]

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 (Oct/Nov 2022). The mark or mark type is shown in brackets.

[2] (a)(i) closed circulation because blood is contained within blood vessels ;
double circulation because blood flows through the heart twice for one complete, circuit of the body / circulation ; A described A pulmonary circulation and systemic circulation
[1] (a)(ii) Q = vena cava and R = aorta;
[3] (a)(iii) I ref to valves
any three from: Q has a: thinner wall; A thinner middle layer wider lumen relative to thickness of wall ; thinner tunica media; (proportionately) less smooth muscle ; (proportionately) less / very few, elastic fibres ;
allow ecf from Q2(a)(ii)
[1] (b)(i) human antibodies, are made of four polypeptides / contain two light chains and two heavy chains ;
[2] (b)(ii) any two from: more / easier to, pass through gaps in, capillary wall / endothelium ; (so) more enter tissue fluid (surrounding tumour cells) ; idea of more cancer cells destroyed quickly ; (smaller so) may not trigger an immune response ;
AVP; e.g. easier to, diffuse / move, through tumour to reach, more / all, cells binds more tightly to antigens on (cancer) cell surface(s) suggestion that makes macrophage response stronger smaller overall size even when drugs attached
[3] (b)(iii) any three from: gives (artificial) passive immunity ;
fast acting/quick response / time not needed for immune response ;
antibody binds to (non-self/foreign) antigen (on surface of a pathogen) ;
antibodies bind to toxins, neutralising them / AW or antibodies act as antitoxins ;
ref phagocytosis;
AVP; e.g. opsonisation bind to flagella and immobilise pathogen antibodies cause, agglutination / clumping / AW, of pathogen