1. Algae are photosynthetic organisms that live in water.
A rapid increase in the population of algae is known as an algal bloom.
Scientists studied the population of algae in a river in the UK at different times of year. Their results are shown in Fig. 21.1.
Fig. 21.1
i. Calculate the percentage decrease in the population of algae between the peak population and 1 November.
percentage decrease = .......................................................... [2]
ii. The river in which the study was conducted is described as a dynamic ecosystem.
Use Fig. 21.1 to explain why this ecosystem could be described as dynamic.
[2]
iii. A student concluded that the increase in population of algae was due to higher temperatures and higher light intensity in the
summer months.
Considering Fig. 21.1 as the student’s data source, discuss the weaknesses in this conclusion.
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, [3]
2(a). In a newly-available area of land, the communities change over time. The process of change is known as succession.
Outline the process of primary succession and explain why heather moorland is an example of deflected succession.
[6]
(b). Heather is a plant with a woody stem that grows on upland areas of the UK such as the North York Moors. These areas are often
described as heather moorland.
Heather moorland is a habitat that is relatively common in the UK but rare elsewhere in the world.
The diagram shows an example of biomass transfer in a heather moorland ecosystem.
The numbers below the arrows represent the percentage of biomass transferred to the species shown in the next trophic level.
Sunlight that can potentially be used in photosynthesis by green plants such as heather is called photosynthetically active radiation (PAR).
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, i. In one year, 8.94 × 109 kJ m–2 of PAR fell on an area of heather moorland.
The heather plants then converted 9.08 × 107 kJ m–2 of this energy into biomass.
Calculate the energy in the PAR that the heather did not convert into biomass.
Energy = .................................. kJ m–2 [2]
ii. Scientists were able to estimate the increase in biomass in heather plants in one year.
Suggest how the increase in biomass over time in a plant such as heather could be determined experimentally.
[1]
iii. Some of the solar radiation that falls on the leaves of plants is reflected. Some solar radiation is of a wavelength that is not
suitable for use in photosynthesis.
List one other reason why much of the PAR is not used by the plant in the production of biomass.
[1]
iv. Suggest and explain why the percentage of biomass transferred between heather and grouse is smaller than the percentage of
biomass transferred between grouse and hen harrier.
[2]
3. Carbon and nitrogen are elements that are recycled.
The flow chart shows the carbon cycle.
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A rapid increase in the population of algae is known as an algal bloom.
Scientists studied the population of algae in a river in the UK at different times of year. Their results are shown in Fig. 21.1.
Fig. 21.1
i. Calculate the percentage decrease in the population of algae between the peak population and 1 November.
percentage decrease = .......................................................... [2]
ii. The river in which the study was conducted is described as a dynamic ecosystem.
Use Fig. 21.1 to explain why this ecosystem could be described as dynamic.
[2]
iii. A student concluded that the increase in population of algae was due to higher temperatures and higher light intensity in the
summer months.
Considering Fig. 21.1 as the student’s data source, discuss the weaknesses in this conclusion.
© OCR 2023. You may photocopy this 1
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page.
, [3]
2(a). In a newly-available area of land, the communities change over time. The process of change is known as succession.
Outline the process of primary succession and explain why heather moorland is an example of deflected succession.
[6]
(b). Heather is a plant with a woody stem that grows on upland areas of the UK such as the North York Moors. These areas are often
described as heather moorland.
Heather moorland is a habitat that is relatively common in the UK but rare elsewhere in the world.
The diagram shows an example of biomass transfer in a heather moorland ecosystem.
The numbers below the arrows represent the percentage of biomass transferred to the species shown in the next trophic level.
Sunlight that can potentially be used in photosynthesis by green plants such as heather is called photosynthetically active radiation (PAR).
© OCR 2023. You may photocopy this 2
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page.
, i. In one year, 8.94 × 109 kJ m–2 of PAR fell on an area of heather moorland.
The heather plants then converted 9.08 × 107 kJ m–2 of this energy into biomass.
Calculate the energy in the PAR that the heather did not convert into biomass.
Energy = .................................. kJ m–2 [2]
ii. Scientists were able to estimate the increase in biomass in heather plants in one year.
Suggest how the increase in biomass over time in a plant such as heather could be determined experimentally.
[1]
iii. Some of the solar radiation that falls on the leaves of plants is reflected. Some solar radiation is of a wavelength that is not
suitable for use in photosynthesis.
List one other reason why much of the PAR is not used by the plant in the production of biomass.
[1]
iv. Suggest and explain why the percentage of biomass transferred between heather and grouse is smaller than the percentage of
biomass transferred between grouse and hen harrier.
[2]
3. Carbon and nitrogen are elements that are recycled.
The flow chart shows the carbon cycle.
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page.
