Ecosystems (OCR GCSE Combined Science A (Gateway): Biology)

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.

(i) Suggest how the students could choose four trees.

 [1]

(ii) The students put their results into a table.  

The LDV is found by adding together the four mean values.

The students calculate the mean number of lichens on the north, east and south sides of the trees.

Calculate the mean for the west side and use this to calculate the LDV.

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

(iii) 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?

 [2]

(iv) LDV is calculated by counting all the lichens present.

What else about the lichens could the students look for to make a better assessment of pollution?

 [3]

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.

(i) The scientists managed to grow crops in the soil. However on Mars, the minerals in the soil would soon run out. Explain why.

 [2]

(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.

 [2]