A-LevelBiologyImmunity9700/21 · Oct/Nov 2017 · Q312 Marks

Cells of the immune system function to protect the body against infectious diseases.

(a)(i)Name the type of cell that produces antibodies.[1]
(a)(ii)The virus that causes the infectious disease influenza has two antigens, H and N. Antibodies are produced in response to an infection by this virus. The antibodies are specific for either antigen H or for antigen N. Describe how the structure of an antibody molecule allows it to be specific for one antigen, such as H or N.[3]
(b)(i)Name the pathogen that causes cholera.[1]
(b)(ii)Describe how the pathogen that causes cholera is transmitted.[2]
(c)(i)Suggest what happens to the structure of a bacterial cell to cause lysis.[2]
(c)(ii)Some scientists believe that bacteriophages could be used to treat people who are infected with cholera. Suggest the properties of the bacteriophages that would make this possible.[2]
(c)(iii)Antibiotics can be used to treat people with cholera. State why antibiotics are not effective against measles.[1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[1] (a)(i) B-lymphocyte / plasma cell; A B-cell / white blood cell / lymphocyte / leucocyte / R beta / ẞ, cells R T-lymphocyte / macrophage / neutrophil
[3] (a)(ii) three from 1 antibody complementary (shape) to antigen ; I matching shape 2 idea that variable regions different for each antibody; 3 (specific) antigen / H / N, binding sites (on antibody); if mp 2 and 3 not gained, allow one mark for antigen binding regions 4 sequence of amino acids / primary structure, varies between antibodies / gives specificity; 5 ref. to difference in, primary structure / amino acid sequence, leading to different, tertiary structure / 3-D shape; 6 ref. to R group interactions between antibody and antigen ;
[1] (b)(i) Vibrio cholerae; I bacterium
[2] (b)(ii) faecal-oral route ;; if mode of transmission not named, allow description infected person faeces / sewage, contaminates, (drinking) water / cooking utensils / vegetable plots / crops / food A diarrhoea for faeces R (human) waste unqualified or ref. to houseflies landing on contaminated faces; uninfected person eating contaminated food / using contaminated utensils / drinking contaminated water ; A bacteria enters water in context of drinking R infected food or water I handling contaminated food need ref. to contaminated once only
[2] (c)(i) cell wall, breaks / damaged / AW A cell wall becomes thinner or cell wall weakened ; plus one from detail of change to cell wall e.g. cross links break down, quantity of murein / peptidoglycan, decreases or cell membrane, breaks / AW or increase in water in cell (so increase in turgor pressure) / AW ;
[2] (c)(ii) two from infect only, V. cholerae / cholera bacteria AW or do not, infect human cells / infect humans; A do not harm human cells do not give side effects / allergic responses, (to humans); able to replicate inside V. cholerae (to produce more bacteriophage for treatment); ref. to remaining, active / infective / AW, with delivery method used / within gut ;
[1] (c)(iii) antibiotics or only effective against bacteria / not effective against viruses do not act on structures possessed by, (measles) virus / Morbillivirus A named structure e.g. protein coat or act on structures that viruses do not have A named structure e.g. murein cell wall or only act on, living / growing, cells or may not be able to reach virus inside (host) cell; AW