Food Production Notes

Edexcel IGCSE Biology: Revision notes

Key facts

  • Glasshouses raise yield by increasing temperature and carbon dioxide, which speed up photosynthesis.
  • Fertilisers add mineral ions such as nitrate; pesticides are fast but can harm other species, while biological control is more sustainable but slower.
  • Yeast respires anaerobically to make carbon dioxide (bread rises) and ethanol.
  • Lactobacillus turns lactose into lactic acid, thickening milk into yoghurt.
  • A fermenter needs aseptic conditions, nutrients, optimum temperature and pH, oxygen and agitation.
  • Fish farming controls water quality, predation, disease, waste and feeding, and uses selective breeding.

Glasshouses

Glasshouses control the conditions so photosynthesis runs faster and crops are protected.

Glasshouses and polythene tunnels trap heat, raising temperature, which speeds up photosynthesis and enzyme activity up to an optimum and can extend the growing season. Carbon dioxide can be added, so it is no longer limiting. Crops are also protected from wind, pests, frost and disease. Yield rises only if light, water and minerals are not limiting.

51015202530354045502468101214161820Temperature / °CRateNormal CO₂Added CO₂
Illustrative curves: photosynthesis rises with temperature to an optimum, and adding carbon dioxide in a glasshouse lifts the whole curve.
  • Higher temperature and CO2faster photosynthesis
  • Faster photosynthesishigher crop yield

Why might raising the glasshouse temperature too far reduce yield?

Fertilisers and pest control

Fertilisers replace lost minerals, and pest control protects crops; each method has advantages and costs.

Fertilisers add mineral ions such as nitrate (for amino acids and proteins), replacing those removed by earlier crops and increasing growth and yield. Pest control protects crops from being eaten or damaged.

  1. 1

    Earlier crops remove mineral ions

    such as nitrate, from the soil

  2. 2

    Fertiliser replaces them

    adding nitrate and other mineral ions

  3. 3

    Plants make amino acids and proteins

    nitrate is needed for protein

  4. 4

    More growth and a higher yield

    if other factors are not limiting

Why fertilisers increase yield.

Pesticides

What it is:
Chemicals that kill pests
Advantages:
Fast-acting and effective
Disadvantages:
Can harm non-target species and build up in food chains; pests may evolve resistance

Biological control

What it is:
A natural predator or parasite of the pest
Advantages:
No chemical residues; more sustainable; pest cannot easily become resistant
Disadvantages:
Slower; the control organism may become a pest itself

Give one advantage of biological control over pesticides.

Yeast and bread

Yeast respires anaerobically, and the carbon dioxide it makes raises bread dough.

Yeast is a single-celled fungus. It respires anaerobically, producing carbon dioxide and ethanol from sugar:

glucose→ethanol+carbon dioxide\text{glucose} \rightarrow \text{ethanol} + \text{carbon dioxide}

The carbon dioxide makes the dough rise and the ethanol evaporates in baking. You can investigate it by measuring the volume of COX2\ce{CO2} collected at different temperatures or sugar concentrations.

  1. 1

    Mix

    yeast, sugar and warm water

  2. 2

    Anaerobic respiration

    glucose becomes ethanol and carbon dioxide

  3. 3

    Dough rises

    trapped carbon dioxide expands the dough

  4. 4

    Baking

    ethanol evaporates

Yeast in bread-making

Which gas makes bread dough rise?

Yoghurt and fermenters

Lactobacillus makes lactic acid that thickens milk; a fermenter grows micro-organisms on a large scale under controlled conditions.

Lactobacillus respires anaerobically, converting lactose into lactic acid. The lower pH coagulates milk proteins, giving yoghurt its texture and sour taste.

An industrial fermenter grows micro-organisms (for insulin or antibiotics) at scale. It needs aseptic precautions, nutrients, optimum temperature and pH, oxygenation for aerobic organisms, and agitation to keep conditions uniform.

  1. 1

    Lactobacillus in milk

    bacteria respire anaerobically

  2. 2

    Lactose to lactic acid

    milk sugar is converted

  3. 3

    pH falls

    milk proteins coagulate

  4. 4

    Yoghurt

    thick, with a sour taste

Making yoghurt

Why is the fermenter stirred (agitation)?

Fish farming

Fish farming controls the fish's conditions and breeding to maximise yield while keeping fish healthy.

  • Water quality: keep oxygen levels up and remove waste.
  • Predation: use nets and cages.
  • Disease: limit stocking density and use treatments.
  • Feeding: provide sufficient, controlled food.
  • Selective breeding: breed from fish with desirable features, such as fast growth.
  1. 1

    Breed from the best fish

    selective breeding for fast growth

  2. 2

    Keep them in nets or cages

    to protect them from predators

  3. 3

    Control the conditions

    oxygen, waste removal, stocking density and disease treatment

  4. 4

    Feed in controlled amounts

    sufficient food for growth without waste

Controlling the conditions on a fish farm.

Control

  • Water quality
  • Predation
  • Disease
  • Feeding
  • Breeding

Method

  • Oxygen levels, waste removal
  • Nets and cages
  • Lower stocking density, treatments
  • Controlled amounts of food
  • Selective breeding for fast growth

Name a way of increasing the yield of farmed fish.

Try an exam question

Describe how yeast is used to make bread rise.

[3 marks]

That's the notes covered.

Carry on to the next subtopic.