Biology · Edexcel Paper 2
Material Cycles
How the carbon cycle, the water cycle and the nitrogen cycle move materials between the living and non-living parts of an ecosystem, how potable water is made in areas of drought, and, for separate Biology, how temperature, water content and oxygen availability affect decomposition in food preservation and composting. Matches Edexcel 9.12 to 9.15 and 9.17 to 9.19. The first three lessons are for both Combined Science and separate Biology; the last lesson is for separate Biology only. There are no Higher tier only parts.
Lessons
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1
The Carbon Cycle
Carbon is in every molecule of every living thing, and the same carbon is used again and again. This lesson is for both Combined Science and separate Biology…
10 terms -
2
The Water Cycle and Potable Water
Every living thing needs water, and the water on Earth is used again and again. This lesson is for both Combined Science and separate Biology. It covers the…
10 terms -
3
The Nitrogen Cycle
Nearly four fifths of the air is nitrogen, yet plants cannot use it and often run short of nitrogen compounds in the soil. This lesson is for both Combined…
10 terms -
4
Decomposition, Food Preservation and Composting
Decay is a nuisance in a fridge and a gift in a garden, and the same three factors control it in both places. This lesson is for separate Biology only…
10 terms -
Knowledge organiser
The whole chapter on a page or two of A4 — to revise from on screen or print.
Key terms in this chapter
All 40, gathered from every lesson.
- Abiotic
- The non-living parts of an ecosystem, such as air, water, soil and rock.
- Biotic
- The living parts of an ecosystem, such as plants, animals and microorganisms.
- Carbon cycle
- The movement of carbon between the air, living things, the soil and fossil fuels.
- Decomposer
- A microorganism, such as a bacterium or fungus, that breaks down dead material and waste.
- Decay
- The breakdown of dead plants and animals and waste by decomposers.
- Combustion
- The burning of a fuel such as wood or coal, which releases carbon dioxide.
- Fossil fuel
- A fuel such as coal, oil or natural gas that formed over millions of years from the remains of living things.
- Deforestation
- The cutting down of forests, which reduces photosynthesis and often releases carbon dioxide.
- Greenhouse gas
- A gas such as carbon dioxide that traps heat in the atmosphere and contributes to global warming.
- Carbon compound
- A substance such as a carbohydrate, protein or fat that contains carbon, which is passed along food chains.
- Evaporation
- The change of liquid water into water vapour, driven by energy from the Sun.
- Transpiration
- The loss of water vapour from a plant, mainly through the stomata of its leaves.
- Condensation
- The change of water vapour into liquid water droplets as it cools, which forms clouds.
- Precipitation
- Water falling from clouds to the ground as rain, snow, sleet or hail.
- Run-off
- Water flowing over the land surface into streams and rivers and back to the sea.
- Potable water
- Water that is safe to drink, with low levels of dissolved substances and microorganisms.
- Desalination
- Removing the dissolved salts from sea water to make potable water.
- Distillation
- Boiling a liquid and condensing the vapour to separate it from the substances dissolved in it.
- Reverse osmosis
- Forcing salty water at high pressure through a partially permeable membrane that lets water through but not the salt.
- Drought
- A long period with much less rain than normal, so that water supplies run short.
- Nitrate
- An ion containing nitrogen that plants take up from the soil to make amino acids and proteins.
- Nitrogen-fixing bacteria
- Bacteria that change nitrogen gas from the air into nitrogen compounds such as ammonia.
- Nitrifying bacteria
- Bacteria that change ammonium compounds into nitrates in the soil.
- Denitrifying bacteria
- Bacteria that change nitrates into nitrogen gas, mostly in waterlogged soil.
- Decomposer
- A microorganism that breaks down dead material and waste, releasing ammonium compounds.
- Legume
- A plant such as a pea, bean or clover that has nitrogen-fixing bacteria in nodules on its roots.
- Root nodule
- A swelling on the root of a legume that contains nitrogen-fixing bacteria.
- Fertiliser
- A substance added to soil to supply the mineral ions, such as nitrates, that plants need.
- Crop rotation
- Growing a different crop in a field each year in a repeating order.
- Mutualism
- A relationship between two species in which both benefit.
- Decomposition
- The breakdown of dead plants, animals and waste by decomposers such as bacteria and fungi.
- Rate of decay
- How quickly dead material breaks down, found from the change in mass divided by the time taken.
- Food preservation
- Treating food so that microorganisms cannot grow and spoil it, by removing warmth, water or oxygen.
- Compost
- Rotted plant waste, made by decomposers, that is added to soil to return nutrients and improve its structure.
- Aerobic
- Using oxygen, as in aerobic respiration by most decomposers.
- Anaerobic
- Without oxygen, as in a waterlogged compost heap where decay is slower.
- Osmosis
- The movement of water from a dilute solution to a concentrated solution across a partially permeable membrane.
- Waterlogged
- So full of water that the air spaces are filled and there is little oxygen.
- Vacuum packing
- Removing the air from a pack of food so that aerobic microorganisms cannot grow.
- Percentage loss of mass
- The change in mass divided by the starting mass, multiplied by 100.