A-LevelBiologyCell structure9700/23 · Oct/Nov 2024 · Q610 Marks

A student constructed a table to compare the structural features of a plant cell, a prokaryotic cell and a virus. Complete Table 6.1. [Table 6.1]

(a)A student constructed a table to compare the structural features of a plant cell, a prokaryotic cell and a virus. Complete Table 6.1.[4]
(b)The cholera bacterium releases a protein toxin called choleragen. The toxin causes the loss of chloride ions and water from epithelial cells into the lumen of the intestine. Fig. 6.1 shows the events that occur in cells lining the intestine when choleragen binds to the membrane of one of these cells. [Figure 6.1]
(b)(i)State one likely source of an outbreak of cholera.[1]
(b)(ii)With reference to Fig. 6.1, state why choleragen molecules are described as having quaternary structure.[1]
(b)(iii)State the type of cell membrane component that forms the receptor for choleragen.[1]
(b)(iv)The process by which chloride ions leave the epithelial cell requires energy. Name the phosphorylated nucleotide that is needed for this process.[1]
(b)(v)Explain why water also moves from epithelial cells into the lumen of the intestine when choleragen is present.[2]

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Mark scheme

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

feature: external structure | plant cell: cell wall composed of cellulose | prokaryotic cell: cell wall composed of peptidoglycan / murein ; | virus: capsid composed of protein / polypeptides ; A capsomeres
feature: size of ribosomes | plant cell: 80S and 70S | prokaryotic cell: 70S ; | virus: no ribosomes
feature: nucleic acids | plant cell: DNA and RNA | prokaryotic cell: DNA and RNA | virus: DNA or RNA ; R DNA and RNA
any one from:
[1] untreated / raw, sewage ; A poor sewage treatment / poor sewer system
[1] contaminated drinking water ;
[1] contaminated food / crops fertilised by raw sewage / seafood contaminated by raw sewage ;
[1] AVP; e.g. newly arrived people infected with, Vibrio cholerae / cholera pathogen (e.g. UN troops in Haiti in 2010)
[1] choleragen is composed of more than one polypeptide ; A 6/7, polypeptides A amino acid chain A composed of, multiple / several, polypeptides
[1] glycolipid / glycoprotein;
[1] ATP / adenosine triphosphate; I adenine triphosphate
[1] chloride ions decrease the water potential of, intestine lumen / outside of cells / AW ; A lower water potential
[1] A loss of chloride ions makes the, cytoplasm / the cells, have a less negative / higher, water potential
[1] (so water, leaves cell / enters lumen) by osmosis / down water potential gradient / from high to low water potential ;

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