Cycles within Ecosystems (Edexcel GCSE Biology: Combined Science)

Figure 1 shows a diagram of the water cycle.

The map in Figure 2 shows the location of the Marshall Islands, an archipelago situated close to Hawaii in the Pacific Ocean.

In 2016, a drought hit the Marshall Islands leading to a severe shortage of drinking water for the inhabitants of the island.

The data in Figure 3 shows the relative volumes of water transferred through each part of the water cycle annually.

Calculate the percentage of the total water transferred that falls through precipitation.

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.

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 gardener wants to use some compost to maximise the vegetable growth in his garden. He has decided to use natural compost and has been told that he should aim for an optimum carbon to nitrogen ratio of 25:1 for the most fertile compost.

Using the Internet, the gardener found the following information (in Figure 1) about the nutrient content of some different types of natural compost.