4.1.4Use of Biological Resources

Crop Plants: Pest Control — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions

5 min read 7 parts Lesson 5 of 15

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Part 1 of 5How pests reduce yield

Insects and other animals

Insects and other animals They eat leaves, stems, fruits and roots, destroying part of the crop or weakening the plant.

Weeds

Weeds Weeds are unwanted plants that compete with the crop for light, water, space and mineral ions.

Fungi

Fungi Fungal infections spread disease through crops, reducing growth and the amount that can be harvested.

Advantages	Disadvantages
Cheap and easy to obtain	Pests can evolve resistance, so the pesticide stops working
Act quickly	Non-specific, so they can kill useful organisms such as pollinating bees
Can remove almost the whole pest population	Persistent ones do not break down and build up along food chains (bioaccumulation), harming top predators
Simple to apply to large areas	Must be applied again and again

Identify the pest species that is damaging the crop, for example whitefly on glasshouse tomatoes.

Choose a natural predator or parasite of that pest, such as a parasitic wasp, or encourage one already present, such as ladybirds eating aphids.

Release the control organism where the pest is found.

The predator and pest populations rise and fall in a cycle, keeping the pest at a lower level rather than removing it altogether.

Advantages	Disadvantages
Natural, so no chemical pollution	Slow to take effect
Pests do not become resistant	Never eliminates the pest completely
Can target one species	The predator may feed on other species instead of the pest
Long lasting and needs no repeated application	The introduced species may not survive, may leave, or may become a pest itself

Term	Meaning
Pesticide	A chemical that kills organisms that damage crops.
Herbicide	A pesticide that kills weeds.
Biological control	Using a living organism, usually a predator, to reduce a pest population.
Resistance	The ability of a pest to survive a pesticide that once killed it.
Bioaccumulation	The build-up of a persistent chemical in organisms higher up a food chain.

Saying biological control wipes out the pest — predator and prey populations cycle, so the pest remains at a lower level.

Claiming pesticides only harm pests — most are non-specific and can kill beneficial insects.

Writing that pests 'get used to' pesticides — resistant individuals survive and breed, so the population becomes resistant.

Forgetting that weeds are a pest because they compete with crops, not because they eat them.

Last updated: 20 October 2026