The water cycle and the carbon cycle, the role of decomposers, what affects the rate of decay, and how compost and biogas make use of it.
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1.Why must materials be cycled in an ecosystem?
The Earth has a finite supply of the elements living things are made from, so they must be returned to the environment to be used again.
2.What do decomposers do?
They break down dead plant and animal matter, releasing the carbon, water and mineral ions locked in it back into the environment.
3.Name the two main groups of decomposers.
Bacteria and fungi.
4.Describe the water cycle.
Energy from the Sun evaporates water from the sea and land. The vapour rises, cools and condenses into clouds, then falls as precipitation, and runs back to the sea.
5.What is precipitation?
Water returning to the land as rain, snow, sleet or hail.
6.Why is the water cycle important to living organisms?
It provides the fresh water that plants and animals need on land, before it drains back to the seas.
7.What is transpiration and how does it fit the water cycle?
The evaporation of water from plant leaves, which returns water vapour to the atmosphere.
8.Which process removes carbon dioxide from the atmosphere?
Photosynthesis by plants and algae.
9.Name three processes that return carbon dioxide to the atmosphere.
Respiration by plants animals and decomposers, combustion of fuels, and the burning of wood.
10.How does carbon pass from plants to animals?
Animals eat the plants, so the carbon compounds in the plant become part of the animal.
11.How is carbon returned to the soil?
When organisms die, decomposers break down their carbon compounds, and waste products from animals do the same.
12.How do fossil fuels fit into the carbon cycle?
They formed from organisms that died millions of years ago. Burning them releases that stored carbon as carbon dioxide.
13.Why is the carbon cycle described as a cycle?
Carbon moves continuously between the atmosphere, living organisms, the soil and the oceans, and is used over and over again.
14.What three conditions speed up the rate of decay?
Warmth, moisture, and the availability of oxygen.
15.Why does warmth increase the rate of decay?
Higher temperature increases the activity of the enzymes in decomposers, up to the point where they denature.
16.Why does decay slow down if it is too hot?
The enzymes in the decomposers denature, so they can no longer break down the material.
17.Why does moisture speed up decay?
Decomposers need water to survive, and moisture helps dissolve and transport the substances they break down.
18.Why does oxygen speed up decay?
Most decomposers respire aerobically, and aerobic respiration transfers far more energy than anaerobic.
19.What is compost?
Decomposed plant material, used by gardeners and farmers as a natural fertiliser.
20.Why do gardeners turn a compost heap?
To let oxygen in, so aerobic decomposers work faster and the material decays more quickly.
21.What is anaerobic decay and what does it produce?
Decay without oxygen. It produces methane gas.
22.What is biogas and how is it made?
A fuel that is mainly methane, made in a biogas generator by anaerobic decay of waste material.
23.Why is biogas useful?
It uses waste material that would otherwise be discarded, and it can be burned as a fuel for heating, cooking or generating electricity.
24.How could you investigate the rate of decay of milk?
Add lipase and an alkali with an indicator, then time how long it takes for the pH to fall as fatty acids are produced. Repeat at different temperatures.
25.Why is it important to control pH in a decay investigation?
The enzymes involved work best at a particular pH, so changing it would affect the rate for reasons other than the variable being tested.
26.Why does food keep longer in a fridge or freezer?
The low temperature slows the enzymes in decomposers dramatically, so decay happens much more slowly.
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