Ecosystems (OCR Gateway GCSE Biology: Combined Science)

Fig. 16.1 shows the water cycle occurring in a lake.

Fig. 16.1

Draw a line to the correct name for the three processes labelled A, B and C in
Fig. 16.1.

Surface run-off water passes through soil and back into the lake.

Write down one reason why surface run-off water is important to organisms living in the lake.

Some students are investigating lichens.

Lichens are often studied because they are sensitive to pollution.

Lichens are made up of two different organisms: a fungi and algae.

Both the fungus and the algae gain from living together.

What biological name is given to a relationship where both organisms gain?

The students find a diagram of a lichen.
Using the information from the diagram suggest what the algae and fungi each gain from their relationship.

algae...........................................................
fungus.........................................................

Lichens are sensitive to pollution because they take up chemicals from the air.

The diagram shows a ‘bushy’ species of lichen and a ‘crusty’ species of lichen.

Bushy lichens are usually more sensitive to pollution than crusty lichens.

Use the diagrams to suggest why.

The students decide to use lichens to try and work out how polluted their school grounds are.

They read about a scale called the Lichen Diversity Value (LDV).

It is worked out in this way:

• choose four trees in the area
• hold a quadrat on the north side of the trunk of one tree
• count the total number of all the lichens in the quadrat
• then do this on the east, south and west side of the tree
• repeat this for each tree.

LDV = .............................. [2]

This scale shows the diversity of the lichens shown by the LDV.

What does the LDV show about the diversity of lichens in the school grounds?

The diagram shows the carbon cycle.
Boxes 1–4 represent different processes in the carbon cycle.

Draw lines to link boxes 1–4 to the correct name for the process in the carbon cycle.

Scientists investigated if crops could be grown on the planet Mars.

They used a soil that was similar to the soil found on Mars. The soil contained some minerals but no living organisms.

The scientists managed to grow crops in the soil. However on Mars, the minerals in the soil would soon run out.

Explain why.

(ii)

Living organisms could be added to the soil but there is no air on Mars. The plants would need to be grown in an enclosed structure.

At first, air would need to be added, but after a while the organisms in the soil and the plants would supply each other with the gases they need.

Explain how this would happen.

Fig. 16.1 shows a plant that grows in South America called stevia.

Fig. 16.1

Fig. 16.2 shows a food web containing stevia.

Fig. 16.2

[1]

[1]

Septoria fungus is a parasite of stevia.

Explain what is meant by the term parasite.

[2]

Gardeners use dead plant material to make compost. They add this compost to soil where they are growing plants.

What do plant roots get from compost in the soil?

Put a  around the correct answer.

carbon dioxide    minerals    nitrogen gas    oxygen gas

Compost can be made in a composting bin. In the bin aerobic bacteria turn dead plant material into compost.

The drawing shows a composting bin.

Explain why the composting bin needs holes in it.

A new way of making compost is called bokashi. In this process the compost is made anaerobically in a different type of composter.

Scientists compare the normal methods of making compost with bokashi.

This is their method:

• Take one large pile of dead plant material
• Divide the material into two samples of equal mass
• Place one sample into the normal composter and place one sample into the bokashi composter
• Measure the temperature in each composter every 10 days
• After 40 days, measure the mass of the compost.

Why did the scientists put the same mass of compost in each composter?

Tick (✓) one box.

Table 20.1 shows the scientists’ temperature measurements.

                                               
                                          Table 20.1

Difference = .......................... °C [2]

Table 20.2 shows the scientists’ results for the mass of the compost.

The mass of the normal compost has decreased by 19kg per day.

Calculate the decrease in mass of the bokashi compost per day.

Give your answer to the nearest whole number.

Decrease = .....................kg per day [3]

Carbon dioxide is given off in the making of the compost. This causes most of the decrease in mass.

Scientists think that the bokashi method of composting might be better for the environment.

Use your answer from part (e)(i) to justify the scientists’ conclusion.

[1]