A-LevelBiologyCell structure9700/23 · May/June 2019 · Q313 Marks

Cholera is an infectious disease caused by the bacterium Vibrio cholerae. The pathogen causes disease by disrupting the activity of the epithelial cells in the human intestine.

(a)Complete Table 3.1 to compare the structure of V. cholerae and an epithelial cell from the human intestine. Use a tick (✔) to indicate the presence of the structure. Use a cross (X) to indicate the absence of the structure. The first row has been completed for you. Table 3.1 cell structure V. cholerae epithelial cell from the human intestine cell wall ✔ X cell surface membrane ribosomes large permanent vacuole organelles surrounded by a double membrane[4]
(b)Describe the methods that can be used to prevent the spread of cholera.[5]
(c)(i)The World Health Organization has suggested that people with HIV/AIDS take a longer time to recover from cholera and are at an increased risk of death from cholera. The human immunodeficiency virus (HIV) only infects certain types of cell. These cells have CD4 receptor proteins in their cell surface membrane. Helper T-lymphocytes have CD4 receptor proteins. Fig. 3.1 is a diagram of HIV showing the glycoprotein gp120. This glycoprotein is embedded in a membrane envelope which surrounds the viral protein coat. [Figure 3.1] The glycoprotein gp120 is important in allowing HIV to only infect certain types of cell. Suggest the role of gp120.[2]
(c)(ii)People with HIV/AIDS have a low helper T-lymphocyte count. Explain how a low helper T-lymphocyte count could reduce the body's ability to produce antibodies against V. cholerae.[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 2019). The mark or mark type is shown in brackets.

[4] one mark each row
cell structure | V. cholerae | epithelial cell from the human intestine
cell wall | ✓ | x
cell surface membrane | ✓ | ✓;
ribosomes | ✓ | ✓;
large permanent vacuole | x | x;
organelles surrounded by a double membrane | x | ✓;
[5] I better sanitation unqualified
I ref. to unclean water
any five from :
ref. to treat drinking water;
A clean / sterilised / chlorinated / safe / bottled / boiled
A ref. to water treatment plants
provide sewage treatment plants ; A treat waste water / containment of sewage / provide latrines (in temporary camps) ;
ref. to keeping sewage and (drinking) water sources separate;
A examples e.g. avoid swimming downstream of sewage outlets
avoid defaecating near rivers used for washing
water treatment plants upstream of sewage disposal
bury faeces
ref. to vaccination / providing vaccines ;
ref. to education in ways to prevent spread;
ref. to (encourage) hand washing;
ref. to food hygiene ; e.g. use of clean cooking utensils / covering food to prevent flies landing / washing food in treated water
/ cook food thoroughly / peel fruit and vegetable washed in (suspected) contaminated water
discourage use of human faeces for fertiliser / use fertiliser other than human faeces / do not irrigate plant food with
contaminated water;
control breeding of, vectors / flies ;
rapid diagnosis;
rapid treatment (for earlier recovery to minimise risk of spreading);
ref. to oral rehydration, salts / therapy ;
use of antibiotics;
ref. to isolation / quarantine ;
[2] to, bind / attach / AW, HIV / virus / pathogen, to, host cell / T-lymphocyte / T-cell;
(because it) binds / is complementary, to, CD4 receptor proteins / AW ;
ref. to binding leads to, entry of virus into cell / endocytosis / fusion of viral envelope with host cell (surface) membrane ;
[2] ref. to less cytokine (released); in context of fewer helper T-lymphocytes
any one from:
(so) fewer B-lymphocytes divide by mitosis / AW ; A humoral response decreased
(so) fewer B -lymphocytes stimulated to differentiate into plasma cells / AW ;
(so) fewer plasma cells to, produce / secrete antibodies ;