Material cycles

Organic substances decay into simpler substances.

The leaves fall off many trees in autumn. The dead leaves contain carbon compounds and nitrogen compounds. Describe how carbon and nitrogen in compounds in the leaves are recycled and used by living trees. You should include a description of:

• how the leaves are broken down

• how substances are taken in and used by the trees.

Students investigated the effect of temperature on the decay of milk. This is the method used.

1. Place 25 cm³ of fresh milk into each of three beakers.

2. Keep one beaker of milk at 5 C.

3. Keep one beaker of milk at 15 C.

4. Keep one beaker of milk at 25 C.

5. Record the pH of the milk in each beaker every day for 4 days.

Table 1 shows the results.

Suggest one improvement the students could have made to the method.

Figure 6 shows the results at 5 C and at 15 C.

Complete Figure 6. You should:

• plot the data for 25 C from Table 1

• draw a line of best fit.

Figure 7 shows the results for 5 C and at 15 C again.

The rate of pH change increases with an increase in temperature. The rate of pH change at 5 C is 0.3 pH units per day. Calculate how many times faster the rate of pH change is at 15 C than the rate of pH

You should draw a tangent on Figure 7.

Milk contains lipids. The lipids are broken down when the milk decays. Explain why the pH changes more quickly when the temperature is higher.

This question is about the effects of deforestation and agriculture. The processes of photosynthesis and respiration affect the carbon dioxide concentration in the air. Figure 9 shows the changes in the carbon dioxide concentration in the air in a tropical rainforest during one day. The data are mean daily values over a whole year.

Explain what causes the changes in the carbon dioxide concentration in the air:

• from 0 to 6 hours

• from 8 to 12 hours.

Use information from Figure 9. 0 to 6 hours

8 to 12 hours

An area of rainforest is cut down and replaced with a field of maize plants. Only one crop of maize is grown each year. Figure 10 shows the changes in the carbon dioxide concentration in the air in the field of maize during one day. The data are mean daily values over the 6-month growing period.

The maize grows for only 6 months of the year. Explain why replacing rainforest with maize will increase the carbon dioxide concentration in the air after one year. Use information from Figure 9 and Figure 10.

A tropical rainforest can contain over 1000 different tree species. Large areas of tropical rainforest have been cut down during the last 100 years so crops can be grown. Scientists studied the regeneration of different areas of tropical rainforest. The scientists:

• investigated areas of rainforest that had been cut down at different times during the previous 100 years

• recorded the number of tree species that re-grew in each area

• compared each area with a control area next to it. The control areas were undisturbed rainforest which had never been cut down.

Figure 11 shows the scientists’ results.

The values plotted in Figure 11 are percentages of the results for the control areas. Explain why the scientists presented their results as percentages.

During the 100 years, the biodiversity of trees in the regenerating rainforest increases.

Give one other conclusion you can make from Figure 11.

Give two reasons why an increase in the diversity of trees in the rainforest leads to an increase in animal diversity.

Energy flows through an ecosystem and materials are recycled. Figure 6 shows the water cycle.

Name process X.

Name the process by which water is absorbed into plant roots.

Give two uses of water in plants.

Figure 7 shows the flow of energy through a food chain. The numbers are in kilojoules/m²/year.

The cow is more efficient than the grass at converting energy. The energy conversion efficiency of the cow is 4.098%. Calculate how many times more efficient the cow is at converting energy than the grass. The equation for energy conversion efficiency is:

Give your answer to 3 significant figures.

Number of times (3 significant figures) =

It is more energy-efficient to rear cows indoors than to rear cows outdoors. Give two reasons why.

Suggest two possible disadvantages of rearing cows indoors.

Decay occurs in a compost heap. Figure 7 shows a compost heap.

Describe:

• how microorganisms in the layers of soil help to recycle chemicals in the dead plants

• how the chemicals are used again by living plants.

Figure 10 shows a flightless bird called the dodo (Raphus cucullatus).

The dodo:

• was 1 m tall

• had a mass of 20 kg

• lived in rainforests on a tropical island

• ate fruits

• made its nest on the ground.

A female dodo laid only one egg each year.

Humans arrived on the island in the year 1507. By 1681 the dodo was extinct.

What is the genus of the dodo?

Tick (✓) one box.

Before the arrival of humans, there were no other large animals living on the island.

Suggest two reasons why the dodo became extinct soon after the arrival of humans.

Today, humans are cutting down large areas of tropical rainforests.

Suggest one use of the land after the trees have been removed.

Why does the removal of trees cause an increase in carbon dioxide in the atmosphere?

Tick (✓) two boxes.

What effect would an increase in carbon dioxide in the atmosphere have on global air temperature?

Tick (✓) one box.

‘Sustainable forestry’ reduces the harmful effects of cutting down trees on the environment.

Figure 11 shows a method of ‘sustainable forestry’.

Numbers 1–9 show different parts of a rainforest.

The trees are cut down in the sequence 1 – 2 – 3 – 4 – 5 – 6 – 7 – 8 – 9

• The trees are cut down in only one area at any one time.

• It takes 30 years to cut down the trees in each area.

• The trees in the ‘Old growth’ area are never cut down.

How many years would it take to cut down the trees in all of the numbered areas in Figure 11 ?

The rainforest contains:

• 750 species of trees

• 400 species of birds

• 150 species of butterflies

• many other species of plants and animals.

Explain how the pattern of cutting down trees shown in Figure 11 stops the biodiversity of the rainforest being reduced.

Many scientists think that global air temperature is related to the concentration of carbon dioxide in the atmosphere.

Figure 14 shows changes in global air temperature and changes in the concentration of carbon dioxide in the atmosphere.

Complete Table 4. Use information from Figure 14.

Choose answers from the box.

You may use each answer once, more than once or not at all.

Many scientists think that an increase in carbon dioxide concentration in the atmosphere causes an increase in air temperature.

How would an increase in the concentration of carbon dioxide in the atmosphere cause an increase in air temperature?

Evaluate evidence for and against the theory that an increase in the concentration of carbon dioxide in the atmosphere causes an increase in air temperature.

Use data from Figure 14 and your own knowledge.

In each year, the concentration of carbon dioxide in the atmosphere is higher in the winter than in the summer.

Give one human activity that could cause the higher concentration of carbon dioxide in the winter.

Give one biological process that could cause the lower concentration of carbon dioxide in the summer.

Give two possible effects of an increase in global air temperature on living organisms.

Many scientists think that global air temperature is related to the concentration of carbon dioxide in the atmosphere.

Figure 3 shows changes in global air temperature and changes in the concentration of carbon dioxide in the atmosphere.

Complete Table 1. Use information from Figure 3.

Choose answers from the box.

You may use each answer once, more than once or not at all.

Many scientists think that an increase in carbon dioxide concentration in the atmosphere causes an increase in air temperature.

How would an increase in the concentration of carbon dioxide in the atmosphere cause an increase in air temperature?

Evaluate evidence for and against the theory that an increase in the concentration of carbon dioxide in the atmosphere causes an increase in air temperature.

Use data from Figure 3 and your own knowledge.

In each year, the concentration of carbon dioxide in the atmosphere is higher in the winter than in the summer.

Give one human activity that could cause the higher concentration of carbon dioxide in the winter.

Give one biological process that could cause the lower concentration of carbon dioxide in the summer.

Give two possible effects of an increase in global air temperature on living organisms.