AS/A-level Biology - Food and Health (2)

• Plants start off all food chains.
• They carry out photosynthesis, where they convert light energy into chemical energy - absorb carbon dioxide from the air and make carbohydrates.
• They also absorb minerals, such as nitrates, from the soil and manufacture a range of other biological molecules.
• Herbivores make use of the biological molecules that the plants make when they eat and digest plants.
• Carnivores eat herbivores and the energy moves along the food chain.
• Humans are omnivores and eat a combination of plants and animals so we gain our energy both directly from plants and indirectly by eating animals.

When it comes to AS/A-level Biology, do you know how selective breeding is used to produce crop plants with high yields, disease resistance and pest resistance?

(i) Selective breeding involves selecting plants with good characteristics (e.g. high yields, disease resistance or pest resistance) to reproduce together in order to increase productivity.

1. Select plants with good characteristics that will increase crop yield and breed them together.
2. Select offspring with the best characteristics and breed them together.
3. Continue this over several generations causing the required characteristic to become more exaggerated.

(ii) Selective breeding can be used to increase the productivity of animals.

1. Select animals with good characteristics that will increase meat yield, e.g. largest cows and bulls, and breed them together.
2. Select offspring with the best characteristics, e.g. largest, and breed them together.
3. Continue those over several generations until cows with very high eat yields are produced, e.g. very large cows.

Fertilisers

• Replaces minerals in the soil that have been removed by previous crops.
• They increase the rate of growth and the overall size of the crops.   

Pesticides

•  Kill organisms/pests that cause diseases in crops - the diseases reduce the yield or kill the crop.
• Many crops are sprayed with fungicides to reduce the effect of fungal growth in the leaves or roots.
• Animals (e.g. sheep) can be dipped to kill ticks that live on their skin under the wool    

Antibiotics

• They reduce the spread of disease by killing/inhibiting the growth of bacteria.
• Such diseases could reduce the growth performance of the animals and may impair reproduction.
• Used to treat problems with the gut of livestock, allowing for efficient digestion causing increased growth.
• Treating the infections reduces the risk of transmitting the pathogens to human consumers, but there are health concerns with the human consumption of meat products that still contain the antibiotics.

• Microorganisms can spoil food in 4 ways:

1. Visible growth - colonies of Mucor and Penicillium can grow on food turning it either black or blue/green.
2. External digestion process - they release enzymes into the food and absorb the nutrients released by breakdown of the food molecules and the food eventually will be reduced to a mush.
3. Releasing Toxins - the bacterium Clostridium botulinum produces a toxin called botulin, causing botulism, which is very dangerous and harmful.
4. Infection - e.g. Salmonella bacteria can be present in poultry products and attack the lining of the stomach and digestive system.

Microorganisms have been used for many years in the manufacture of food and drinks. For example,

• Microorganisms can increase rapidly under the right conditions, so food can be produced more quickly.
• Microorganisms can grow on a range of inexpensive materials.
• The environment can be artificially controlled - so food could grow any time of the year.
• The food products made from the microorganisms often lasts longer in storage than the raw product they are made from, e.g. cheese can be stored longer than milk.
• Quorn contains no animal fat or cholesterol so is more healthy.

• High risk of contamination - conditions could be favourable to harmful microorganisms causing food to spoil or cause illness, e.g. food poisoning.
• Small changes in the conditions (temperature and pH) can easily kill the microorganism.
• Quorn - some consumers may not want to eat fungal protein which has been grown on waste.

(1) Salting - Prevents microorganisms taking in water and dehydrates them as water leaves the microorganisms by osmosis.

(4) Freezing - Slows down reactions taking place in microorganisms so growth and reproduction is slow.
 

(5) Heat Treatment - Kills microorganisms, e.g. pasteurising involves heating to 72oC for 15 seconds and then cooling rapidly to 4oC, killing harmful microorganisms.

That's the end of the topic!

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Drafted by Bonnie (Biology)