Biology

Homework The carbon and Nitrogen Cycles

Please make sure that your questions on the carbon cycle are complete and in detail.

Please write half a page about the nitrogen cycle. The notes below will help.

Please answer the questions about the nitrogen cycle. I will collect it all on friday.

The Carbon Cycle key points:

· The air contains about 0.04% carbon dioxide

· Plants use the carbon atoms in CO₂ to make sugars

· When sugars are respired by plants and animals the carbon atoms in the sugar become CO₂ again

· Decomposers convert the dead organic matter to CO₂ when they break down and respire the material

1. What effect on carbon dioxide levels does cutting down the rain forest have? Explain your answer

2. Why is it important that there is a replantation programme to replace trees that are cut down?

The Nitrogen Cycle Key points:

· The air is made up of about 79% nitrogen (N₂)

· N₂ is not reactive and plants can?t use it directly

· Nitrogen is changed into a usable form by nitrogen fixation:

Lightning, some nitrogen is converted to oxides and this with water forms nitrates

Nitrogen-fixing bacteria, these live in the root nodules of some plants (beans, clover, peas) and can convert nitrogen into nitrates

· Artificial fertilizers, nitrogen and hydrogen are reacted together to form ammonia (NH₃). Ammonium compounds make up fertilisers

· Some plants get their nitrogen source directly from animals e.g. the Venus Fly trap.

· Denitrifying bacteria, these turn the nitrates in the soil back into nitrogen gas

1. Explain why nitrates are a usable form of nitrogen for plants

2. Explain why farmers often add fertilisers to the soil

3. Explain why Carnivorous plants are able to cope with boggy soils which are low in nitrate levels

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Biology