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Date May 2021 Marks available 2 Reference code 21M.2.HL.TZ1.2
Level Higher level Paper Paper 2 Time zone Time zone 1
Command term State Question number 2 Adapted from N/A

Question

The image shows part of a plant cell with a chloroplast in close proximity to mitochondria.

[Source: Photo © E. Newcomb.]

State two structural similarities between mitochondria and chloroplasts.

1.

2.

 

[2]
a.

Compare and contrast mitochondria and chloroplasts in terms of the substrates they use and the products they produce. 

[2]
b.

Outline how the compounds produced by chloroplasts are distributed throughout the plant.

[3]
c.

Markscheme

a. (a loop of) DNA ✔

b. 70S ribosomes ✔

c. double membrane ✔

d. electron transport chains/enzyme complexes in (internal) membranes ✔

e. enzymes in a region of fluid/in stroma and matrix ✔

f. large area of (internal) membrane/cristae and thylakoids ✔

Only two answers should be marked – the first on each line.

Do not award marks for functions rather than structures, for example ATP production.

Allow spaces inside cristae and thylakoids for mpf.

a.

a. ATP produced by both / ADP used by both ✔

b. oxygen produced by chloroplasts and used by mitochondria ✔

c. carbon dioxide produced by mitochondria and used by chloroplasts ✔

d. carbon/organic compounds built up in chloroplasts/anabolism and broken down in mitochondria/catabolism ✔

Do not award mpd for statements about carbohydrates or glucose (because the pyruvate used by mitochondria is not a carbohydrate).

b.

a. in phloem ✔

b. loading into sieve tubes/by active transport/by cotransport/by companion cells ✔

c. entry of water (to phloem) by osmosis/because of high solute concentration ✔

d. causes high/hydrostatic pressure ✔

e. flow from high pressure to lower pressure down pressure gradient ✔ from source to sink ✔

Do not award mpa if xylem included with phloem.

Do not award a mark solely for mentioning the term ‘translocation'.

c.

Examiners report

Surprisingly few candidates achieved two marks for this question, with many thinking that these organelles were cells with cell membranes, cell walls or even nuclei.

a.

To answer this question, candidates had to know that chloroplasts photosynthesize and mitochondria respire aerobically. They then had to compare or contrast the substrates or products of these two processes. The mean mark was 0.6 out of 2, showing that many candidates failed to do this. Well-prepared candidates had no difficulty.

b.

This question also required a link to be made, after which marks were relatively easily earned. The phase 'distributed throughout the plant' indicated that it was carbon compounds, not oxygen, that were the issue, so phloem transport was the distribution method expected. Transport of oxygen out through stomata and transport within leaf cells were not relevant to the question as asked. The average score was only 0.6 out of 3.

c.

Syllabus sections

Core » Topic 1: Cell biology » 1.2 Ultrastructure of cells
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