The carbon cycle

A student investigated the decomposition of two different types of leaf.

The student placed 200 grams of holly leaves in a net bag.

The student placed 200 grams of oak leaves in another net bag.

The bags were left in a classroom.

The mass of the leaves in each bag was recorded every 10 days for 50 days.

State two variables that would need to be controlled in this investigation.

The results of this investigation are shown in Figure 16.

Calculate the rate of decomposition of holly leaves from 0 to 50 days.

Compare the trends shown in the data for holly leaves and oak leaves.

Explain why it is important for the environment that dead leaves are decomposed.

Name one type of organism that decomposes leaves.

Leaves are eaten by snails.

1 600 grams of leaves and 10 snails were kept in a container for one month.

A scientist measured the mass of the leaves and the mass of the snails at the start and end of one month.

Figure 17 shows the results.

Explain why the change in mass of the leaves is not the same as the change in mass of the snails.

4 A student investigated the decomposition of two different types of leaf. The student placed 200 grams of holly leaves in a net bag. The student placed 200 grams of oak leaves in another net bag. The bags were left in a classroom. The mass of the leaves in each bag was recorded every 10 days for 50 days.

(a) State two variables that would need to be controlled in this investigation.

(b) The results of this investigation are shown in Figure 4.

Figure 4

(i) Calculate the rate of decomposition of holly leaves from 0 to 50 days.

(ii) Compare the trends shown in the data for holly leaves and oak leaves.

(c) Explain why it is important for the environment that dead leaves are decomposed.

(d) Name one type of organism that decomposes leaves.

(e) Leaves are eaten by snails. 1 600 grams of leaves and 10 snails were kept in a container for one month. A scientist measured the mass of the leaves and the mass of the snails at the start and end of one month. Figure 5 shows the results.

Explain why the change in mass of the leaves is not the same as the change in mass of the snails.

1 Figure 1 shows a bird called an egret on the back of a buffalo.

(Source: © Jaromir Chalabala/Shutterstock)

(a) (i) The egret eats parasites that live on the skin of the buffalo. Which term describes this relationship, where the buffalo and the egret both benefit?

(ii) The buffalo is part of the carbon cycle. Use words from the box to complete the sentences.

The buffalo gains carbon from the_{..............................................................} in the plants that it eats. Bacteria will_{..............................................................} the waste from the buffalo.

(iii) Figure 2 shows part of the carbon cycle. Draw and label an arrow on Figure 2 to show the process plants use to make glucose from carbon dioxide.

(b) Enzymes are used to digest proteins. Figure 3 shows an enzyme and a protein.

Explain how boiling the enzyme stops the protein being digested.

Figure 16 shows a photomicrograph of two stomata in a leaf.

The length of one guard cell in this image is 6 mm.

Convert the length of this guard cell into micrometres (µ m).

The image has been magnified 150×.

Calculate the actual size of the guard cell.

Give your answer in standard form in mm.

Explain the role of denitrifying bacteria in the nitrogen cycle.

*(c) Describe how carbon is cycled through the biotic and abiotic components of an ecosystem.

1 (a) Figure 1 shows part of the carbon cycle.

(i) Name the process that transfers carbon from plants to animals.

(ii) Use words from the box to complete the sentences.

Plants use carbon dioxide from the atmosphere for_{....................................................................} Animals release carbon dioxide and energy during_{....................................................................}

(iii) Which of these can be a decomposer?

(b) The water cycle is the movement of water through an ecosystem. Which process is used to obtain freshwater from seawater?

(c) Water from rivers can be filtered and then treated with chemicals to make it suitable for drinking.

(i) Give one reason why water is filtered.

(ii) Give one reason why water is treated with chemicals.

(a) A student was investigating the populations of organisms in a garden.

Figure 15 shows the estimates of the number and biomass of some of the organisms in the garden.

Calculate the biomass of the population of earthworms in the garden.

Hedgehogs eat slugs and earthworms. Slug pellets were used to kill the slugs.

Explain how killing the slugs would affect the population of earthworms in this garden.

Describe a method that could be used to estimate the population of slugs in the garden.

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

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

(a) A student was investigating the populations of organisms in a garden.

Figure 2 shows the estimates of the number and biomass of some of the organisms in the garden.

Calculate the biomass of the population of earthworms in the garden.

Hedgehogs eat slugs and earthworms. Slug pellets were used to kill the slugs.

Explain how killing the slugs would affect the population of earthworms in this garden.

Describe a method that could be used to estimate the population of slugs in the garden.

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

Figure 12 shows the global movement of carbon into or out of the atmosphere.

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 13 shows his first experiment.

in a bell jar
minutes

State why the candle was not burning after three minutes.

Joseph Priestley continued the investigation but placed a plant inside the bell jar as shown in Figure 14.

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.

State two variables that would need to be controlled to compare these two experiments.

Nitrogen is cycled through the environment.

Describe the roles of bacteria in the nitrogen cycle.

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 5 shows one of these bags.

The net bags were then put in trays and covered in soil as shown in Figure 6.

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 7 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.

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

State two improvements to the method for this investigation.