Food ProductionEdexcel IGCSE Biology: Revision notes

Glasshouses and polythene tunnels are used to increase crop yield by controlling environmental conditions:

• They trap heat, raising temperature, which increases the rate of photosynthesis and enzyme activity (up to an optimum) and can extend the growing season
• Carbon dioxide levels can be artificially increased inside, removing CO2 as a limiting factor and increasing the rate of photosynthesis
• They protect crops from wind, pests, frost and disease

Both increased CO2 and increased temperature (within a suitable range) increase crop yield by increasing the rate of photosynthesis, provided other factors (light, water, minerals) are not limiting.

Fertilisers add mineral ions (e.g. nitrate, for making amino acids/proteins) to the soil, replacing those removed by previous crops and increasing plant growth and yield.

Pest control protects crops from being eaten or damaged:

• Pesticides — chemicals that kill pests; advantages: fast-acting, effective, increase yield quickly; disadvantages: can harm non-target/beneficial species, can accumulate in food chains, pests may evolve resistance
• Biological control — using a natural predator or parasite of the pest; advantages: no chemical residues, more sustainable, pest cannot easily develop resistance; disadvantages: slower acting, the control organism can become a pest itself if it spreads beyond the target area

Yeast is a single-celled fungus used in bread-making. Yeast respires anaerobically, producing carbon dioxide and ethanol from sugar:

glucose → ethanol + carbon dioxide

In bread-making, the carbon dioxide produced makes the dough rise, and the ethanol evaporates during baking. Anaerobic respiration by yeast can be investigated by monitoring gas production (e.g. volume of CO2 collected) under different conditions such as temperature or sugar concentration.

Lactobacillus bacteria are used to make yoghurt: they respire anaerobically, converting lactose (milk sugar) into lactic acid, which lowers the pH, causing milk proteins to coagulate (thicken) and giving yoghurt its sour taste and texture.

An industrial fermenter is used to grow micro-organisms (e.g. for making insulin or antibiotics) on a large scale. Suitable conditions must be maintained:

• Aseptic precautions — to prevent contamination by unwanted micro-organisms
• Nutrients — a continuous supply for growth
• Optimum temperature and pH — maintained (often with cooling jackets/probes) for maximum enzyme/growth activity
• Oxygenation — for organisms that respire aerobically
• Agitation (stirring) — to keep conditions uniform and micro-organisms evenly suspended

Fish farming methods aim to maximise yield while keeping fish healthy:

• Maintaining water quality (e.g. oxygen levels, removing waste)
• Controlling predation (e.g. nets, cages)
• Controlling disease (e.g. limiting stocking density, treatments)
• Removing waste products
• Controlling feeding (providing sufficient, controlled food)
• Selective breeding (choosing fish with desirable characteristics, e.g. fast growth, to breed from)