Ecosystems (Edexcel International A Level (IAL) Biology): Exam Questions

Lions, giraffes and acacia trees are found on the African Plains.

The diagram shows the energy in the trophic levels that these organisms occupy.

Give the meaning of each of the following terms, using the information in the diagram to illustrate your answer.

(i) Habitat

(2)

(ii) Population

(2)

(iii) Community

(2)

(iv) Niche

(2)

Calculate the efficiency of energy transfer between trophic level one and trophic level two.

Stages of succession can be seen on different parts of a sand dune system.

The greater the distance of the sand dune from the sea, the later the stage of succession.

The diagram shows a sand dune system and the table gives some information about the different types of sand dune in this system.

(i) The pH of a solution is a measure of the concentration of hydrogen ions in that solution.

It is a log scale e.g. a solution of pH 5 contains 10^-5 mol dm^-3 of hydrogen ions.

What is the difference in concentration of hydrogen ions in a fore dune compared with a grey dune?

(1)

☐ A a fore dune has 2 times more hydrogen ions than the grey dune

☐ B a fore dune has 2 times fewer hydrogen ions than the grey dune

☐ C a fore dune has 100 times more hydrogen ions than the grey dune

☐ D a fore dune has 100 times fewer hydrogen ions than the grey dune

(ii) Calculate the percentage increase in the number of plant species on the grey dune compared with the fore dune.

(1)

(iii) Explain the changes in these sand dunes with distance from the sea.

Use the information in the table to support your answer.

(6)

Sand dunes can be classified as fixed dunes, semi-fixed dunes and shifting dunes.

The graph shows the mean net primary productivity (NPP) above the ground and below the ground for these three types of sand dune.

(i) Describe the conclusions that can be drawn from this graph.

(3)

(ii) Explain how the products of the light-independent reactions become NPP below the ground.

(4)

Scientists studied the distribution of biomass in organisms on Earth.

State the meaning of the term biomass.

Voronoi diagrams were used to present some of the data.

Two Voronoi diagrams are shown.

Diagram A shows the biomasses of groups of organisms.

Diagram B shows the biomasses of the organisms in the animals group.

The biomass is given in gigatons of carbon (GtC), where 1 GtC = 10¹⁵ g of carbon.

The area of each polygon is proportional to the biomass of that organism. The shape of each polygon has no meaning.

(i) Calculate the percentage of biomass in organisms belonging to the domain Eukarya.

Use the information in diagram A.

(2)

(ii) Suggest why the scientists studied the distribution of biomass in groups of organisms and not the number of individual organisms.

Use the information in diagram A.

(2)

(iii) Discuss the advantages and disadvantages of presenting data in Voronoi diagrams.

Use diagram B to support your answer.

(3)

The same study also determined the distribution of biomass in three different environments: marine, deep underground and land.

The Voronoi diagram shows the distribution of biomass in each environment.

The graph shows the proportion of biomass in different groups of organisms.

Explain the distribution of biomass in these three environments.

Use the information in the Voronoi diagram and the graph to support your answer.

The photograph shows a polar bear.

Emma, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

Polar bears are adapted to live in the Arctic Circle.

Polar bears have a layer of fat beneath their skin. This fat insulates them from the cold and can be used to supply the polar bear with water (metabolic water).

They have a thick fur coat which also insulates them from the cold.

Polar bears feed on seals. The polar bear sits on the ice and waits for a seal to come to the surface of the water to breathe.

Which row of the table describes the types of adaptation of polar bears?

What is the niche of a polar bear?

Suggest why the polar bear needs to rely on the store of fat to provide it with water.

Climate change is resulting in habitat fragmentation. Habitat fragmentation causes groups of polar bears to become separated from one another.

Explain the effect that habitat fragmentation could have on the genetic diversity of polar bears.

Ticks are parasites that live in the fur of moose.

Ticks are thought to be responsible for the decline in the number of moose.

The table shows the frequency distribution of ticks in a population of moose.

(i) Calculate the percentage of moose that have 50 000 or more ticks on their bodies.

(2)

(ii) The diagram shows the life cycle of the tick.

The ticks feed on the blood of the moose. One tick can remove 200 to 600 times its body mass.

The ticks irritate the moose. The moose will scratch against trees causing large clumps of fur to fall off.

Explain how global warming might affect the life cycle of ticks and result in the decline in the number of moose.

Use all the information in the question to support your answer.

(6)

A student wanted to investigate the effect of light intensity on the abundance of ribwort plantain (Plantago lanceolata) on two separate areas of a school field.

Plan an investigation that the student could carry out to compare the abundance of ribwort plantain in the two areas with different light intensity.

In another investigation a student collected data from 10 quadrats along a transect which extended at 90 degrees from the edge of a woodland.

To test whether there was a significant association between distance from the woodland and percentage cover of the plant dog's mercury (Mercurialis perennis), the student decided to calculate the Spearman's rank correlation coefficient (r_s).

The table below shows the ranked data for each quadrat.

Complete the table and use the formula below to calculate r_s. Give your answer to 3 decimal places.

$r_s=1-\frac{6\Sigma d^2}{n(n^2-1)}$

The critical value of r_s at p = 0.05 for n = 10 is 0.648.

State the conclusion that can be drawn from the investigation described in (b). Use your calculated r_s value and the table of critical values to support your answer

Compare and contrast the terms community and ecosystem.

Surtsey, a volcanic island off the southern coast of Iceland, was formed by underwater volcanic eruptions that began in 1963. When the eruptions ceased, the island consisted entirely of bare rock with no living organisms. Scientists have monitored the colonisation of the island by living organisms ever since.

State the term that describes this process of colonisation and the resulting development of a community.

The table shows data collected at Surtsey at five intervals after the eruption.

*Using the data and your own knowledge, explain the changes in species richness and vegetation cover observed over this period.

A scientist studied energy flow in a salt marsh ecosystem on the east coast of England. Salt marshes are highly productive coastal ecosystems containing plants such as common samphire (Salicornia europaea).

Which correctly describes gross primary productivity (GPP) in the salt marsh ecosystem?

In one area of the salt marsh, the GPP of Spartina was 22 400 kJ m⁻² year⁻¹. Plant respiration accounted for 6720 kJ m⁻² year⁻¹. Primary consumers assimilated 1168 kJ m⁻² year⁻¹.

Calculate the efficiency of energy transfer from Spartina to the primary consumers. Give your answer to two significant figures.

S. europaea was grown in laboratory conditions under continuous bright light. The concentration of carbon dioxide supplied to the plant was then suddenly reduced.

Explain the changes in the concentrations of RuBP and GP in the leaves during the first few minutes after this reduction.

Which of the following correctly describes the role of ATP in the chloroplasts of the S. europaea plants?

State the precise location of the light-independent reactions within the cells of S. europaea.