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SECTION A
Candidates must answer all questions in the spaces provided.

1. Very large numbers of microscopic algae exist in ocean communities away from land.
Approximately half of all photosynthesis on Earth occurs in these algae. They also carry out cell
respiration. Marine biologists investigated ocean water at a series of depths at many sites. They
measured the changes in oxygen content of the water in the light and in the dark.
From their measurements they calculated:
- the rate of oxygen production by the photosynthesising algae
- the rate of oxygen use in cell respiration by the whole community.

The difference between the rate of oxygen production and oxygen use is the net oxygen
production of the community.
The results for one site in the North Atlantic are shown below:

Oxygen production and net oxygen production /✙ mol O 2 dm −3 day−1

-2 0 2 4 6 8
0

Key
20 net oxygen
production
Depth / m oxygen
production
40

60

[Source: P J le B Williams, Nature, (1998), 394, pages 55-57]

(a) (i) Using only the data in the graph, outline the relationship between depth and net oxygen
production from 0 to 30 metres. [2]
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(ii) Suggest a hypothesis to account for this relationship. [2]

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(Question 1 continued)

(b) The graph shows that at 53 and 60 metres depth the net oxygen production was higher than
at 30 metres. Explain this increase, using the data in the graph. [2]

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The marine biologists combined the data for all depths and calculated the total amounts of
photosynthesis and cell respiration for the site in the North Atlantic and for other ocean sites
around the world. The results are plotted in the scattergram below. The dotted line links points at
which oxygen production by photosynthesis and oxygen use in cell respiration would be equal.

300

Total amount
of cell respiration
/ mmol O 2 m −2 day −1 200

100

0
100 200 300
Total amount of photosynthesis / mmol O 2 m −2 day −1

(c) Although there is considerable variation in the data, the scattergram shows an overall
relationship between total amounts of photosynthesis and cell respiration.

(i) State the relationship. [1]

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(ii) Suggest an explanation for the relationship, based on the activities of autotrophs and
heterotrophs in the community. [2]

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(Question 1 continued)

The sites used in the investigation are a representative sample of the Earth’s oceans.

(d) Using the data in the scattergram, identify whether the total amount of photosynthesis or cell
respiration was larger in most of the sites. [1]

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Some ocean regions contain significantly fewer algae than other regions. One possible reason for
this is low levels of iron (Fe) in the water. To test this hypothesis 225 kg of iron, in the form of
soluble salts, was scattered in a 72 km 2 area of the Pacific Ocean containing few algae. This was
done on one day in May 1995.

The chart below shows the carbon dioxide concentration of the water in the release area and
surrounding area in the nine days following the release of the iron salts.

[Source: Coale et al, Nature (1996) 383, pages 495-501]

(e) (i) Using only the data in the charts, outline the effect of release of iron on carbon dioxide
concentration in the water. [2]
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(ii) Explain the effects of release of iron on carbon dioxide concentrations. [2]
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(Question 1 continued)

(f) Using the data in this question, discuss whether iron release in the Earth’s oceans would
reduce global warming. [3]
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2. (a) Define interspecific hybridisation. [1]

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(b) (i) State what is done to change a species using transgenic techniques. [2]

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(ii) Outline one ethical objection to the use of transgenic techniques. [2]

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(iii) State one example of the use of transgenic techniques. [1]

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