Ecosystems (Edexcel International A Level Biology)

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.

(2)

(2)

(2)

(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.

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)

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.

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)

The cassava root is an important food crop grown in the tropics.

The photograph shows organelles containing starch granules inside cassava root cells, as seen using an electron microscope.

(1)

(3)

The graph shows the mass of five food crops grown in Africa. It also shows the world production of these crops.

(1)

Answer ............................ million tonnes

Some plants contain chemicals that protect them from being eaten by animals.

These chemicals taste bitter and can be converted by enzymes into hydrogen cyanide.

Hydrogen cyanide inhibits respiration and can cause death.

Cassava can be grouped into two main varieties: bitter cassava and sweet cassava.
These varieties differ in the concentration of the bitter-tasting chemicals.

Processing of the cassava removes most of these chemicals.

The graph shows the mean dry mass of these cassava varieties when grown in the same conditions.

The table gives information about three crop plants.

Discuss the advantages and disadvantages of growing these three crop plants for human food.

Use the information in the question to support your answer.

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.

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

Use the information in diagram A.

(2)

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)

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.