Ecosystems (OCR GCSE Biology A (Gateway))

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]

Some students measured the temperature inside a compost heap.

They also measured the external temperature.

On five occasions they mixed up the compost heap with garden forks.

The graph shows their results.

(i) The compost took 63 days to completely decompose.

Explain how the students could tell this from their graph.

 [1]

(ii) The rate of temperature increase is greatest before the compost is mixed for the first time.

Explain how the rate of temperature change can be calculated.

 [1]

Compost decomposes more slowly above 60°C or below 30°C.

Use ideas about enzymes and decomposition to explain why this is.

Use the graph to describe how the forking helps to provide the best temperature for decomposition.

The rock pocket mouse is a small grey coloured mouse that lives in Mexico.

These mice are the main food for owls.

Rattlesnakes also feed on these mice.

The mice get most of their food from grass plants and grass seeds.

(i) How many trophic levels are there in the feeding relationships described?

 [1]

(ii) Draw a labelled pyramid of biomass for these feeding relationships.

[2]

The diagram shows part of a food web from a grassland.

How many secondary consumers are shown in this food web?

A survey was set up to see if the number of badgers and hedgehogs has changed in the UK.

The number of badgers and hedgehogs were counted in different areas each year from 2003 to 2012.

The graph shows the results.

Use the food web to suggest an explanation for the change in the number of hedgehogs shown in the graph.

The diagram shows part of a food web from a woodland.

(i) Great tits are described as both primary consumers and secondary consumers.

Explain why.

 [2]

(ii) Foxes are described as both predators and competitors of pine martens.

Explain why.

 [2]

(iii) Which organism in the food web occupies the second trophic level?

 [1]

Great tits and flycatchers are both birds.

In a conservation project, scientists have built boxes for the birds to nest in. The scientists fixed the boxes on trees at different heights.

The table shows how many birds of each type used the boxes for nesting.

(i) Draw a bar chart on the graph paper to show the scientists’ results.

The results for great tits and flycatchers should be on the same axis.

[4]

(ii) The food web shows:

• Weasels feed on great tits

• Pine martens feed on flycatchers.

Weasels live on the ground but pine martens live in trees.

How can this be used to explain the results of the scientists’ investigation?

 [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]

This machine helps shred plants for a compost heap.

The machine can shred plants into three different sizes.

This graph is in the instruction booklet for the machine.

Which size of plant pieces is best for making compost?

Explain your answer.

The size of the plant pieces has an effect on the number of microorganisms in the compost.

Suggest why.

The decomposition of dead plants and animals is an important process for ecosystems.

Explain why.

The diagram shows the flow of biomass through an agricultural food chain.

(i) Calculate the percentage efficiency of transfer of biomass between the cattle food crop and humans.

Answer = ......................... % [2]

(ii) Write down two ways that biomass is lost from the food chain.

1 .............................
2 .............................

[2]

High levels of light intensity can damage plants. To prevent damage, plants have a protection mechanism.

When light intensity levels get too high, the protection mechanism switches on. This stops the plant absorbing too much light.

When the light intensity drops to safe levels, the protection mechanism switches off slowly. 

Explain why this mechanism would reduce the biomass available to humans.

Higher tier only

Switching off the protection mechanism described in part (b) involves the plant making a protein.

Scientists have put extra copies of the gene for this protein into the plants. This makes the plant make more mRNA molecules.

(i) Explain why making more mRNA will switch off the mechanism faster.

[2]

(ii) Scientists have found that the genetically modified plants make 20% more biomass.

Use the agricultural food chain from part (a) to calculate the increase in biomass this would provide for humans.

Answer = ....................................... kg [2]

(iii) Inserting extra copies of a plant’s gene into a plant is a type of genetic modification (GM).

Another example of GM involves inserting a bacterial gene into a plant which makes the plant produce an insecticide.

People are more likely to support genetic modification involving extra copies of the plant gene, rather than inserting the bacterial gene.

Suggest reasons why.

[2]

A gardener buys a composter to decay plant material as quickly as possible.

The composter has three sections.

She designs an experiment to see if watering makes the plant material decay faster. She waters:

• Section A once a week

• Section B once a month

• Section C is not watered.

The gardener wants valid results. Explain one factor that the gardener should keep constant.

The gardener measures the temperature in each section for five months.

She knows that heat is given off when plant material decays.

The graph shows her results.

(i) Write down two differences between the change in temperature in Section A and the change in temperature in Section C.

1. ..........................................
2. ..........................................

[2]

(ii) The gardener decides that she should water all sections every week.

Explain why she decides this.

[1]

Each section of the composter has holes in it to let oxygen in.

Explain why this helps the material to decay.

The diagram shows the flow of biomass through an agricultural food chain.

(i) Calculate how much biomass is lost between the plants and humans.

Answer = .....................kg [1]

(ii) One way biomass is lost from the food chain is by insects eating the leaves of plants.

Write down one other way that biomass is lost from the food chain.

[1]

The plants grown for cattle food often have their leaves eaten by insects.

Scientists have produced genetically modified (GM) plants that make insecticide in their leaves.

(i) Explain why these GM plants would make more biomass available to humans.

In your answer use the diagram of the agricultural food chain and ideas about photosynthesis.

[6]

(ii) Suggest two reasons why some people are against this type of genetic engineering.

[2]

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

(i) Write down the number of trophic levels in this food web.

[1]

(ii) What is the source of energy for this food web?

[1]

(iii) Septoria fungus is a parasite of stevia.

Explain what is meant by the term parasite.

[2]

The leaves of stevia taste very sweet. People are now trying to grow stevia as a crop.

Stevia farmers often add nematode worms to their fields.

Explain why farmers do this.

Use Fig. 16.2 in your answer.

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

 (i) The scientists’ results for the normal compost are plotted on the grid.

Complete the graph by plotting the results for the bokashi compost and draw a curve of best fit.

[3]

(ii) Describe the change in the temperature of the normal compost during the investigation.

[2]

(iii) Use data from Table 20.1 to calculate the difference between the maximum temperature of the normal compost and the maximum temperature of the bokashi compost.

Difference = .......................... °C

[2]

(iv) Which two statements explain this difference in temperature between the two types of compost?

Tick (✓) two boxes.

[2]

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

(i) 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]

(ii) 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]