GCSE OCR Chemistry - Food Matters C3

GCSE Chemistry

Unit C3 - Food Matters

Recycling Elements

Organic and Intensive Farming

Pest Control

Natural Polymers


Insulin and Diabetes

Harmful Chemicals in Food

Food Additives

Keeping Food Safe

Eating Healthily

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Recycling Elements

Elements are constantly being recycled.

1. As plants grow they take in elements like OXYGEN, NITROGEN and CARBON through their leaves and roots

2. When the plants die and decompose most of these elements are replaced and returned to the soil.

3. Some of the elements in plants become part of animals too when the plants are eaten. These elements are also returned to the environment when the animals poo or when they die and decompose.

4. Dead animal and plant matter (and poo) is broken down by MICROBES. They convert it into compounds that are taken up by the other plants and the process starts again.

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The Nitrogen Cycle

1. Plants absorb nitrates from the soil using their roots. Nitrogen is needed by plants and animals to make proteins.

2. Animals have to eat plants to get their nitrogen.

3. Organic waste (like rotting plants, animals or poo) is broken down by MICROBES called decomposers into AMMONIUM COMPOUNDS.

4. Nitrifying Bacteria turn the AMMONIUM COMPOUNDS produced by the microbes into useful nitrates.

5. These nitrates can then be absorbed by the roots of green plants once again.

6. Nitrogen-fixing bacteria live in the soil and the roots of some plants that can make nitrates directly from nitrogen in the air. Energy from lightning can also make nitrogen and oxygen in the air react to give nitrates in the soil. Denitrifying bacteria breaks down nitrates in the soil to give nitrogen in the air again - the opposite to nitrogen fixing bacteria.

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Harvesting Crops

Harvesting crops removes elements from the soil. Crops are eventually harvested from the soil so they can be sold and eaten.

1. The removal of the crops means that some of the elements that the plants use to grow are taken out and not replaced like they would be then the plants die and decompose.

2. Elements that are lost include NITROGEN, PHOSPHORUS and POTASSIUM.

3. These elements need to be replaced or the fertility of the soil will decrease and the next crops won't grow properly.

4. Farmers can replace these elements using organic or intensive farming methods.

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Organic Farming - Replacing Lost Elements

Organic Farmers don't use artificial fertilisers to replace the elements in the soil. Instead, they use natural substances and processes.

1. They put animal manure, compost and human sewage onto their land as fertilisers. The human sewage is heat-treated first to destroy any harmful microbes.

2. Manure, sewage and compost all contain waste plant material so they replace elements that plants take out of the soil in the same way as a natural cycle would.

3. Organic farmers also grow GREEN MANURE. Plants are grown on fields and then ploughed in and left to rot. Plants like clover are often used because they have nitrogen fixing bacteria in their roots which add nitrates to the soil which can then be used by the next crop.

4. Crop rotation is also used. It is where farmers grow different crops each year in a cycle in relation to whether they have nitrogen fixing bacteria or not and how much nitrogen they need/use.

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Intensive Farming - Replacing the Lost Elements

1. Intensive farmers use man-made artificial fertilisers to put the elements back into the soil.

2. Because artificial fertilisers use pure chemicals (they're not full of plant matter) it is easy to use just the right amount. Farmers can use small volumes of artificial fertilisers because they contain much higher percentages of the elements the crops need than manure does.

3. Artificial fertilisers are spread on the ground as pellets or sprayed onto the crops as they grow.

4. The amount of each nutrient can be chosen to be exactly right to a particular plants needs.

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Pest Control

Pests and diseases are a nightmare for farmers because they can seriously reduce the crop yields.

1. Some pests, like aphids, are insects that eat crop plants.

2. Diseases like potato blight can damage or kill crop plants.

Luckily, most pests and diseases can be controlled depending on whether the farm is organic or intensive.

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Pest Control - Organic

Organic farmers are not allowed to use artificial pest control methods which are man made to deal with pests and disease.

1. Pests can be controlled by using NATURAL PREDATORS - This is known as a BIOLOGICAL CONTROL. For example, ladybirds can be introduced into greenhouses to prey on greenfly pests.

2. Crop Rotation as mentioned previously, is used to prevent the pests and disease causing organisms of one particular crop plant building up in an area.

3. Field edges are left grassy to encourage larger insects and other animals that feed on pests.

4. Varieties of plants that are best able to resist pests and disease are chosen.

5. Natural Pesticides are used. Some pesticides are completely natural, and as long as they are used responsibly they dont mess up the ecosystem.

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Pest Control - Intensive

Intensive farmers SPRAY their crops with man-made chemicals to destroy pests and kill diseases on the crops.

1. Chemical pesticides are more effective than organic methods as they usually kill ALL of the pests and disease-causing organisms whereas organic methods can't.

2. This means BIGGER YEILD of crops with FEWER BLEMISHES.

3. But, the spraying leaves a chemical residue on the crop which could harm humans eating the plants as well as the pests.

4. chemical pesticides kill indiscriminately which means it not only kills the pests but it also kills other organisms that could be beneficial.

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Organic Farms

Organic farmers have to follow certain rules. It is illegal to sell food as ORGANIC if it hasn't been produced that way.

1. The UK Government has set national standards that have to be met by organic farmers, like concerning the use of chemicals.

2. The national rules ban the use of virtually ALL artificial chemicals and set standards for the way that pests and diseases are controlled. the levels of pesticides and other artificial chemicals in the soil have to be below a certain level before a farm can be classed as organic.

3. The standards for meat that is classed as organic are just as strict. The animals must be allowed to more around freely, can only be fed on organic feed and can't be given artificial hormones to make them grow quicker. They are not given medication unless it is really necessary, unlike intensively reared animals which are given antibiotics as a matter of course because infections are so common.

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Carbohydrates are a group of compounds that include sugars (the monomers) and the polymers cellulose and starch. They are all made up of the same elements - CARBON, HYDROGEN and OXYGEN.

1. Carbohydrate comes from the fact it is made of CARBON and WATER (H20)

2. The simplest carbohydrate is the sugar glucose (C6H12O6). This is the sugar that plants make from carbon dioxide and water by PHOTOSYNTHESIS.

3. Other carbohydrates like starch (for energy storage in plants) and cellulose are made by linking glucose molecules together in chains.

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leah murray


brilliant revision cards well done!



really useful! thanks. =)

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