How do we produce enough food while managing the effects of fertilisers and pesticides?
Food security and the need to increase food production, the use of fertilisers and the problem of algal blooms, the use of pesticides and bioaccumulation, and the alternatives of biological control and GM crops.
An SQA National 5 Biology answer on food production, covering food security and the need to increase food production, the use of fertilisers and the problem of algal blooms, the use of pesticides and bioaccumulation, and the alternatives of biological control and GM crops.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
The SQA wants you to explain food security and why food production must increase, describe how fertilisers raise yield and the problem of algal blooms, explain pesticides and bioaccumulation, and describe the alternatives of biological control and GM crops.
Food security
The challenge is that the human population is growing while the amount of farmland is limited, so food production has to increase without simply clearing more wild land. This is why farmers use fertilisers, pesticides and improved crops, each with benefits and drawbacks.
Fertilisers and algal blooms
The problem comes if fertiliser washes (leaches) into rivers and lochs:
- The extra nitrates make algae grow rapidly, forming an algal bloom.
- The bloom blocks light, so the water plants below die.
- Bacteria decompose the dead plants and use up the oxygen in the water.
- With little oxygen, fish and other organisms die, and biodiversity falls.
Pesticides and bioaccumulation
Pesticides are chemicals used to kill pests that would otherwise reduce crop yield. The problem is that some pesticides are non-biodegradable.
Alternatives: biological control and GM crops
To reduce the use of chemicals, farmers can use:
- Biological control: introducing a natural predator of the pest to keep its numbers down, instead of spraying pesticide.
- GM (genetically modified) crops: crops whose genetic material has been altered to improve a characteristic such as higher yield or resistance to pests or disease.
Examples in context
Example 1. DDT and birds of prey. The pesticide DDT bioaccumulated up food chains and reached high concentrations in birds of prey such as ospreys, thinning their eggshells and causing breeding to fail. This real example shows why non-biodegradable pesticides are now restricted.
Example 2. Ladybirds against aphids. Gardeners and growers release ladybirds, which eat aphids (greenfly), as a form of biological control. This keeps the pest down without spraying chemicals, avoiding bioaccumulation and protecting other wildlife.
Try this
Q1. State what nitrates from fertiliser are used to make in a plant. [1 mark]
- Cue. Amino acids and proteins (and DNA).
Q2. Name one alternative to chemical pesticides for controlling pests. [1 mark]
- Cue. Biological control (using a natural predator).
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style4 marksExplain how fertilisers increase crop yield, and describe the problem that can follow if they leach into a loch.Show worked answer →
A 4-mark answer should cover the benefit and the chain of harm.
Fertilisers contain nitrates. Plants take up nitrates and use them to make amino acids, proteins and DNA, which lets the crop grow more, increasing yield.
If fertiliser leaches into a loch, the extra nitrates cause algae to grow rapidly, forming an algal bloom.
The bloom blocks light, so water plants below die. Bacteria decompose the dead material and use up the oxygen in the water.
With little oxygen, fish and other organisms die, reducing biodiversity.
Markers reward (1) nitrates used to make proteins, raising yield, (2) algal bloom forming, (3) light blocked and plants dying, and (4) bacteria using up oxygen, killing organisms.
SQA N5 style2 marksExplain what bioaccumulation is and why it is a problem for top predators.Show worked answer →
Two ideas: the build-up and the effect at the top.
Bioaccumulation is the build-up of a non-biodegradable pesticide as it passes along a food chain, becoming more concentrated at each higher level.
Top predators eat many organisms from lower levels, so the pesticide reaches its highest concentration in them and can poison or harm them.
Markers reward (1) the pesticide building up and becoming more concentrated up the chain and (2) the harm to top predators.
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Sources & how we know this
- SQA National 5 Biology Course Specification — SQA (2019)