9.3 Cycles within Ecosystems

Figure 1 shows an outline of the carbon cycle.

Figure 1

Describe the roles of living organisms in the cycling of carbon.

Suggest a consequence to the living world of substances such as carbon not being recycled. 

Figure 1 shows the carbon cycle.

Deforestation has an impact on both the carbon cycle and the water cycle.

Describe and explain the effect of deforestation on levels of carbon and water in the atmosphere.

Figure 2 shows the carbon dioxide concentration of the atmosphere between 1955 and 1995.

Nitrogen is an essential element for plant growth. Most plants can only use nitrogen in the form of nitrate ions. Only legumes that have bacteria living in root nodules, as shown in Figure 1, can use nitrogen from the air.

Figure 2 shows the nitrogen cycle. Different stages have been numbered 1 to 8.

Earthworms are invertebrates that live in the soil. As they move through the soil, they create air pockets between the soil particles.

Suggest why this may lead to an increase in nutrients in the soil.

The effect of temperature on decomposition was investigated.

30 leaves were collected.
The mass of five leaves was recorded and the leaves were placed into a net bag.
This was repeated five more times.

Figure 1 shows one of these bags.

Figure 1

The net bags were then put in trays and covered in soil as shown in Figure 2.

Figure 2

Which type of tray should be used so that the leaves are in the best conditions for decomposition?

Each tray was kept at a different temperature.

The mass of the leaves was recorded again after 25 days.

Figure 3 shows the results of this investigation.

Calculate the percentage decrease in mass for the leaves at 85 °C.

Give your answer to two significant figures.

(2)

(ii)

Explain which temperature was the best for the decomposition of the leaves.

(2)

(iii)

State two improvements to the method for this investigation.

Plants use nitrate ions to make proteins and chlorophyll.

Figure 1 shows part of a root as seen using a light microscope.

Figure 2 shows information about the two types of cell labelled in Figure 1.

Figure 2

(i)

Calculate the surface area to volume ratio of the root hair cell.

Algae are green plants.

Figure 3 shows the number of algae in a lake in the United Kingdom during one year.

Explain the changes in the number of algae in the lake from February to June.

A student investigated the effect of nitrate ion concentration on plant growth.

She placed barley seedlings in three test tubes containing different concentrations of nitrate fertiliser.

Test tube 1 contained distilled water with 1 pellet of nitrate fertiliser.
Test tube 2 contained distilled water with 2 pellets of nitrate fertiliser.
Test tube 3 contained distilled water with 3 pellets of nitrate fertiliser.

After 7 days, the lengths of the seedlings were measured.

Figure 1 shows an example of the apparatus used.

Figure 1

(2)

Figure 1

Which hazard does this symbol represent?

(1)

(1)

Figure 2 shows the results of this investigation.

Figure 2

Farmers use crop rotation to reduce the need to add nitrate fertilisers to the soil.

Plants such as peas and beans have a mutualistic relationship with nitrogen-fixing bacteria.

Explain why farmers use these plants in their crop rotation cycle.

Explain how cabbages, earthworms and squirrels contribute to the carbon cycle.

Figure 1 shows the global movement of carbon into or out of the atmosphere.

Figure 1

Calculate the net mass of carbon added to the atmosphere each year.

Joseph Priestley was a scientist who investigated how green plants and combustion affected the carbon cycle.

Figure 2 shows his first experiment.

Figure 2

(1)

Joseph Priestley continued the investigation but placed a plant inside the bell jar as shown in Figure 2.

Figure 2

He observed that the candle stayed alight for two minutes more than the candle in the bell jar in the first experiment.

Explain his observation.

(2)

Nitrogen is cycled through the environment.

Describe the roles of bacteria in the nitrogen cycle.

State three ways the concentration of nitrates in soil can be increased.

A student investigated the decomposition of leaves from different types of tree.

Decomposers in the soil convert...

The student collected and weighed some fresh leaves from a beech tree.

• The leaves were placed on top of soil in a tray.
• This was repeated for leaves from three other types of tree.
• The trays were kept in the same abiotic conditions for 40 days.
• The leaves were reweighed after 40 days.

(2)

Figure 1 shows the mean rate of decomposition for this investigation.

Figure 1

The same investigation was extended to include the leaves of a silver birch tree.

The starting mass of the leaves was 28.2 grams.

After 40 days the mass of the leaves was 19.7 grams.

Calculate the rate of decomposition of the leaves of the silver birch tree.

Give your answer to three significant figures and include the units.

(3)

Explain how the concentration of oxygen in a compost bin would affect the rate of decomposition.

In Ireland during the 19th century, a mould caused potato plants to rot.

Explain how this mould affected food security in Ireland.

A group of pupils investigated the effect of temperature on mould growth on bread.

Figure 1 shows the bread after being kept at different temperatures for seven days.

Figure 1

Which is the best estimate of the percentage cover of mould on the bread at 40 °C?

(1)

State two conclusions that can be made about the growth of mould on the bread from 0 °C to 40 °C shown in Figure 1.

(2)

Explain why there was no mould growing on the bread kept at 60 °C.

(2)

Figure 2 shows some part-baked bread in a sealed bag.

The gas in the bag is nitrogen, which prevents the bread from going mouldy.

Figure 2

If the bag is opened, the bread goes mouldy within days.

State why the bread goes mouldy.

Explain why keeping food in a fridge slows down the growth of mould.