Ecosystems

Limpets are marine animals that attach to rocks on coastal shores. The diagram shows a food web that contains limpets.

Which are the trophic levels of the starfish in this food web?

State what is meant by the term population.

Explain why only 1% of the energy in the algae is transferred to the starfish.

Some scientists think that food webs on rocky shores are at risk from an increase in greenhouse gases. The scientists record these two factors during August every year for 17 years.

• the number of limpets per m² on a rocky shore

• the mean temperature at the same rocky shore

The graph shows the scientists’ results.

Describe how the scientists could determine the number of limpets on the rocky shore.

Give one factor the scientists should control when comparing the number of limpets per m² each year.

The scientists conclude that the combustion of fossil fuels is a risk to the food web. Discuss the scientists’ conclusion. Use the information in the graph and your own knowledge to support your answer.

The diagram shows a forest food web.

How many secondary consumers are there in this food web?

Which term describes all the organisms in the food web together with their environment?

The fox receives 1% of the energy present in the oak tree. The fox receives 0.04% of the energy present in the grass. Explain why a higher proportion of the energy reaches the fox from the oak tree than reaches the fox from the grass.

A student uses this method to estimate the total area of the woodland floor that is covered by grass.

• randomly place a 0.25 m² quadrat in one location of the woodland

• estimate the percentage of the quadrat that is covered by grass

• repeat at one other location

• calculate the mean percentage covered by grass for both quadrats

• measure the total area of the woodland floor

• calculate the total area of the woodland covered by grass.

State why the student placed the quadrats randomly at each location.

Explain how the student could improve their method, to obtain a more reliable estimate of the total area of woodland covered by grass.

The diagram shows the dimensions of the woodland.

The student finds the mean percentage of the two quadrats covered by grass

Use this value to calculate the total area of the woodland floor covered by grass.

total area covered by grass =_........

The diagram shows part of a woodland food web.

Which organism is a primary consumer in this food web?

Which of these describes the woodland community?

This is one food chain from the food web.

A student counted 20 mice living around 4 oak trees. There were also 2 foxes in the area.

Draw a labelled pyramid of numbers for this food chain on the grid.

Your pyramid should be drawn to scale.

Photosynthesis results in 25 000 kJ of energy being transferred to the biomass of the oak trees each year.

Only 8% of this energy is transferred to the biomass of the 20 mice each year.

Calculate the mean amount of energy transferred to the biomass of one mouse each year.

Explain why only 8% of the energy stored in the biomass of the oak trees is used by the mice for growth.

The diagram shows part of a food web from an ecosystem in a region of North America.

Which of these organisms in the food web is a primary consumer?

State what is meant by the term ecosystem.

Wolves were hunted in this region of North America until they became extinct in 1926.

The extinction of wolves damaged the ecosystem in these ways.

• the population of mice, hawks and beavers decreased

• the population of producer species decreased

Beavers are important in this ecosystem because they cut down old trees and create shelters that other organisms nest in.

Discuss why the extinction of wolves damaged the ecosystem.

In 1995, 14 wolves were reintroduced to this region.

The diagram shows the change in wolf population from 1996 to 2016.

Calculate the percentage change in the wolf population between 1996 and 2004.

Suggest why the wolf population changed between 2004 and 2012.

The reintroduction of wolves caused changes in the populations of some plant species.

Describe how the population size of a plant species in the region could be determined.

A student studies the organisms in a pond community.

Which of these is the correct description of a community?

The table shows the number of organisms per m² at different trophic levels in a pond community.

It also shows the total biomass of these organisms per m².

Trophic level	Number of individuals per m2	Total biomass in g per m2
secondary consumers	100	1.0
primary consumers	1.5 104	2.5
producers	7.2 1010	17.5

Calculate the mean mass in g of a single primary consumer.

Give your answer in standard form.

Use the grid to draw a pyramid of biomass for the pond community.

The number of secondary consumers is low because energy transfer is not 100% efficient.

Explain why egestion is one reason why energy transfer is not 100% efficient.

Give two other reasons why energy transfer is not 100% efficient.