5a Food Production¶

Part of 5 Use of Biological Resources.

Food production applies biology to farming, fermentation and fish farming. The common idea is to find the factor that limits yield or survival, and then control it.

What You Need to Learn¶

Further detail: Pearson Edexcel International GCSE Biology specification.

How glasshouses, fertilisers and pest control increase crop yield, how micro-organisms are used to make bread and yoghurt, and how industrial fermenters are controlled. Biology-only students also learn how fish farming is managed.

Crop Production¶

Glasshouses and polythene tunnels enclose crops in a controlled environment. Each benefit removes a factor that would otherwise limit photosynthesis or damage the crop:

Control	How it works	Why it raises yield
Weather protection	The structure shields the crop	Harsh conditions cannot damage growth
Carbon dioxide	Paraffin lamps or gas burners add CO₂	Carbon dioxide is no longer the limiting factor in photosynthesis
Temperature	The glass or plastic traps heat, and extra heating can be added	The temperature stays near the optimum for the enzymes of photosynthesis
Pest exclusion	The enclosed space keeps out many insects	Fewer pests damage the crop

Fertilisers supply the mineral ions that plants need. Nitrates are used to make amino acids for proteins, phosphates are needed for respiration and root growth, and potassium supports enzyme function and healthy flower and fruit development. Fertilisers are water-soluble, so roots can absorb the ions by active transport.

Pest control stops insects, fungi and weeds damaging crops. There are two approaches:

Method	Advantages	Disadvantages
Chemical pesticides (insecticides, fungicides, herbicides)	Quick and effective, and can remove a whole pest population	Pests can evolve resistance; they are non-specific, so they can kill beneficial organisms; they can build up along food chains and harm other animals; they must be reapplied
Biological control, using a predator or parasite of the pest	No chemical residues, and the effect lasts	Slower; an introduced species can become a pest itself; it cannot remove the pest entirely

Worked example: percentage increase in yield

A crop gives 4.0 tonnes per hectare in an open field and 5.2 tonnes per hectare in a glasshouse with extra carbon dioxide.

Percentage increase = (5.2 − 4.0) ÷ 4.0 × 100 = 30%

The increase is calculated against the original yield, which is the open-field value.

Exam technique

A question asking you to evaluate pest control wants both methods weighed against each other, with a reason for each point. For example, "pesticides are fast, but they are non-specific, so they can kill the bees that pollinate the crop". Saying that one is "better" without a reason is not evaluation.

Food Production by Micro-organisms¶

Yeast and bread making. Yeast is a single-celled fungus. In dough, with little oxygen, it respires anaerobically by fermentation:

glucose → ethanol + carbon dioxide

The carbon dioxide is trapped as bubbles, which makes the dough rise, and the ethanol evaporates during baking.

Investigating yeast fermentation:

Dissolve sugar in boiled and cooled water.
Mix yeast into the solution in a boiling tube.
Add a thin layer of oil on top, so oxygen cannot enter and the conditions are anaerobic.
Connect the tube to a test tube of limewater, which turns milky when carbon dioxide passes through it.
Count the bubbles over a set time.
Change one variable, such as temperature in a water bath or the sugar concentration, and repeat.

Yoghurt using Lactobacillus. Lactobacillus is a bacterium that feeds on lactose, the sugar in milk, and produces lactic acid:

All equipment is sterilised to kill unwanted micro-organisms.
The milk is pasteurised, heated to about 72 °C for 15 seconds, to kill any bacteria in it.
The milk is cooled and Lactobacillus is added.
The mixture is incubated at about 40 °C in a fermenter, where the bacteria change lactose into lactic acid.
The lactic acid lowers the pH, which denatures the milk proteins, and this gives yoghurt its thick texture.
Flavourings, colourings or fruit are added before packaging.

Industrial Fermenters¶

An industrial fermenter is a large vessel in which micro-organisms are grown to make a useful product, such as insulin, enzymes, antibiotics or food. The conditions have to be controlled, because the micro-organisms are living cells with enzymes.

Condition	Reason
Aseptic conditions	Prevent contamination by unwanted micro-organisms, which would compete with the culture or spoil the product
Nutrient supply	The micro-organisms need an energy source and raw materials such as carbon and nitrogen to grow and make the product
Optimum temperature and pH	Keeps the enzymes working at the maximum rate without denaturing them
Oxygen supply	Provides oxygen for aerobic respiration in organisms that need it
Agitation (stirring)	Spreads nutrients, oxygen, micro-organisms and heat evenly through the vessel

Exam technique

For a fermenter, give each condition and its reason. "Keep the temperature at the optimum so the enzymes work fastest" is a complete point, but "keep it warm" is not.

Biology-Only Content¶

This content is required for Biology-only students and is not required for Combined Science students.

The section below, on fish farming, is Biology-only.

Fish Farming¶

Fish farming uses biological management to raise yield efficiently. Each method controls a factor that would otherwise reduce growth or survival:

Method	Explanation
Maintaining water quality	Water is filtered to remove waste and harmful bacteria, which prevents disease
Controlling intraspecific predation	Fish of the same species are separated by size and age, which reduces competition and cannibalism
Controlling interspecific predation	Different species are kept apart with nets or tanks, so they cannot prey on each other
Disease control	Antibiotics treat infections, and good water quality reduces the risk of disease
Removing waste	Filtration removes faeces, which would lower oxygen levels and promote disease
Controlling feeding	Frequent small feeds give growth without wasted food
Selective breeding	Fish with desirable features, such as fast growth or disease resistance, are bred together

Common Confusions¶

Anaerobic yeast: Fermentation in bread and in the yeast investigation happens without oxygen. The oil layer is what makes it anaerobic.
Pasteurisation vs sterilisation: Pasteurisation heats milk briefly to kill harmful bacteria. Sterilising equipment kills all unwanted micro-organisms.
Why yoghurt thickens: The lactic acid lowers the pH, which denatures the milk proteins.
Intraspecific vs interspecific: Intra means within one species, and inter means between different species.

Check Yourself¶

Give two ways in which a glasshouse increases crop yield.
State what mineral ion plants need nitrates for.
Write the equation for fermentation in yeast, and explain why dough rises.
Explain why a layer of oil is added to the yeast mixture.
Explain why the temperature and pH in an industrial fermenter are controlled.
(Biology only) Give two ways in which fish farmers reduce losses from predation and disease.

Answers

Any two of: adding carbon dioxide so it is not limiting; keeping the temperature near the enzyme optimum; protecting from weather; keeping out pests.
To make amino acids, which are used to make proteins.
Glucose → ethanol + carbon dioxide. The carbon dioxide forms bubbles that are trapped in the dough, so it rises.
The oil stops oxygen entering the mixture, so the yeast respires anaerobically and produces carbon dioxide that can be measured.
The enzymes of the micro-organisms work fastest at their optimum. If the temperature or pH moves away from it, the enzymes work more slowly or are denatured, and less product is made.
Any two of: separating fish by size, age or species; filtering the water; using antibiotics; removing waste.

Key Terms¶

Fertiliser: a substance containing mineral ions added to soil to support plant growth.
Pesticide: a chemical used to kill organisms that damage crops.
Biological control: using a living organism to control a pest species.
Fermentation: anaerobic respiration in yeast or bacteria that produces useful products such as ethanol, CO₂ or lactic acid.
Lactobacillus: a bacterium that converts lactose into lactic acid, used in yoghurt production.
Pasteurisation: brief heating used to kill harmful microorganisms in liquids.
Fermenter: a sealed vessel used to grow microorganisms under controlled conditions for industrial production.
Aseptic conditions: conditions that prevent contamination by unwanted microorganisms.
Agitation: mixing or stirring in a fermenter to keep conditions uniform.
Fish farming (aquaculture): the controlled rearing of fish in tanks or pens as a food source.
Intraspecific predation: predation between individuals of the same species.
Interspecific predation: predation between individuals of different species.