Cycles within Ecosystems Practice Questions

Name process A.

Name process B.

Process C releases carbon dioxide from dead remains and waste.

Name the group of organisms that carry out process C.

Name process A.

Name process B, in which water vapour changes into the tiny water droplets of a cloud.

Name process C.

Name process D, in which water vapour is lost from the leaves of the tree.

Which type of bacteria converts ammonia in the soil into nitrates?

A denitrifying bacteria

B nitrifying bacteria

C nitrogen-fixing bacteria

D decomposing bacteria

State the role of nitrogen-fixing bacteria in the nitrogen cycle.

Name the type of bacteria that convert nitrates in the soil into nitrogen gas.

State why grass plants need to take up nitrate ions from the soil.

Peas are frozen at $-18\ ^\circ\text{C}$ soon after they are picked.

Explain why freezing the peas slows down decay.

Onions can be preserved by pickling them in vinegar.

Explain why pickled onions do not decay quickly.

Calculate the mean rate of decomposition of the grass clippings.

Include the units in your answer.

rate of decomposition = ..............................................

Once a week the gardener mixes the contents of the bin with a garden fork.

Explain how mixing the compost increases the rate of decomposition.

The gardener moves the compost bin from a shaded place to a sunny place. The compost inside the bin becomes warmer.

Explain why the compost now decomposes more quickly.

State what is meant by potable water.

Describe how sea water can be made into potable water by distillation.

Reverse osmosis can be used instead of distillation.

Explain one advantage of using reverse osmosis rather than distillation to produce potable water.

Explain why materials such as carbon and nitrogen must be recycled between the biotic and abiotic components of an ecosystem.

Describe how decomposers release carbon dioxide and mineral ions from the dead leaves.

Explain why plants need nitrate ions, and the effect on the lettuces of a shortage of nitrate ions in the soil.

Instead of buying more fertiliser, the gardener digs the remains of the old lettuce plants into the soil.

Explain how this increases the amount of nitrate available to the next crop.

Give two variables the student should have controlled in this investigation.

Calculate how many times faster the milk turns sour at $30\ ^\circ\text{C}$ than at $4\ ^\circ\text{C}$.

.............................................. times faster

The time taken for the milk to turn sour falls by only $2$ hours between $30\ ^\circ\text{C}$ and $40\ ^\circ\text{C}$.

Suggest an explanation for this.

Coal is a fossil fuel formed from trees that died in swamps about 300 million years ago.

Some of the carbon atoms that were in one of these trees are now part of carbon dioxide molecules in the air.

Explain how the carbon in the tree became part of the coal, and how it has been returned to the air as carbon dioxide.

Calculate the mean rate of decay of the leaf litter during the first $20$ days, in grams per day.

.............................................. g per day

Calculate the percentage of the original mass of leaf litter that had decayed after $80$ days.

.............................................. %

The rate of decay of the leaf litter decreased as the investigation went on.

Explain why.

Explain why the concentration of nitrates in the soil falls when the soil is waterlogged.

After the field has drained, the farmer could add ammonium nitrate fertiliser or well-rotted manure to the soil.

Explain why adding manure supplies nitrate to the crop for a longer period of time than adding ammonium nitrate fertiliser.