Environmental impacts of food production
Trace how fertiliser runoff, pesticides and land clearing can affect water, food chains, air and soil.
On this page
Sources of Food · about 25–35 min
What you need to understand
Link the named method to a specific pathway and consequence; “it causes pollution” leaves the explanation unfinished.
Definitions
- soil erosion
removal of fertile topsoil by water or wind
For example: Clearing forest leaves soil less protected from erosion.
Explanation
A useful crop treatment can have effects outside the field. After rain, dissolved fertiliser can be carried into a stream. The added nutrients encourage excessive growth of algae and water weeds. Fertiliser does not create haze: the pathway here is field → runoff water → extra nutrients → increased aquatic growth.
Pesticides and herbicides can contaminate soil or water beyond the intended target. Organisms may take up harmful substances; when another organism eats them, the substances can pass along the food chain. For example, small water animals → fish → bird is a food chain: each arrow points from the food to the organism eating it. A contaminant in the small water animals can pass to the fish and then to the bird. Do not substitute the fertiliser-and-algae explanation for this chain.
Burning vegetation releases smoke that contributes to haze and can cause breathing difficulties. Clearing forest is deforestation. It also removes protective plant cover and roots that help hold soil, so rain can wash exposed soil away more easily. Smoke and soil erosion are different pathways from the same land-clearing method.
Evaluate the supplied observations separately: did usable food increase, and what environmental change occurred? A lower crop-damage percentage can show a benefit while a fall in non-target insects suggests a cost. Neither one observation nor the word “natural” proves that a method is safe in every setting. Ask what was compared, what else changed and whether the result was repeated.
Pause and say it: Link the named method to a specific pathway and consequence; “it causes pollution” leaves the explanation unfinished.
Common mistake
Tempting wrong idea: Fertiliser used on land cannot contaminate nearby water.
Why it fails: Rain can move substances beyond the field. A treatment’s target does not set a boundary that keeps every chemical away from other organisms.
Use this instead: Fertiliser can enter water and stimulate excessive growth of algae and water weeds.
Worked examples
Modelled example 1
Fertiliser near a stream
Problem
Crop yield rises after fertiliser use, but algae increase downstream. Explain a possible benefit and a pathway to the environmental cost.
Study the worked solution
Reason from the evidence
Method
Separate the intended crop benefit from the downstream environmental observation.
Reason
For every method, ask: what problem does it solve, and what new problem might it cause?
Working
- Mineral nutrients can improve plant growth.
- Rain can carry excess nutrients into water.
The same method can therefore bring a production benefit and an environmental cost.
State the conclusion
Working
Evaluate both increased yield and water contamination rather than labelling fertiliser simply good or bad.
Common misconception 2
Does pesticide stay only on the pest?
Learner response
“Once sprayed, pesticide affects only the insect pest and cannot enter water or a food chain.” Identify the unsupported assumption.
Trace one pathway away from the crop
View solution step by step
Follow the substance
Method
Describe spray reaching non-target organisms, soil or runoff water.
Reason
A chemical applied outdoors is not confined automatically to the intended pest.
Working
Harmful substances may enter organisms and transfer along a food chain.
Challenge 3
Judge a method from two columns
Problem
These illustrative observations come from two similar fields in one season.
| Treatment | Crop damaged / % | Non-target insects counted in the same sampling time |
|---|---|---|
| No pesticide | 30 | 80 |
| Pesticide | 8 | 18 |
Give a balanced conclusion using both columns. Name one extra piece of evidence needed before recommending repeated use.
Use benefit, cost and uncertainty
Hints
Hint 1: use both columns
One column shows production benefit; the other shows an ecological cost.
Hint 2: avoid one-trial certainty
Consider repeats, other sites or evidence about which insects were affected.
View solution step by step
Balance the measured outcomes
Method
State the large reduction in crop damage and the large fall in non-target insects.
Reason
A production decision cannot be judged from yield protection alone.
Working
The pesticide was effective against crop damage but was associated with a substantial non-target cost.
Request stronger evidence
Method
Ask for repeated fields or seasons and identification of affected organisms.
Reason
Weather, site conditions and natural population changes could influence one comparison.
Working
Recommendation should wait for replicated evidence of both effectiveness and environmental impact.
Guided practice
Try it with support
A farm uses fertiliser to raise yield, while algae increase in a nearby stream. Explain the benefit and the environmental cost.
Link the same mineral nutrients to two locations.
Check the guided answer
Answer: Fertiliser supplies mineral nutrients that may limit crop growth, increasing yield. Runoff carries excess nutrients into the stream, encouraging excessive algae and water-weed growth.
Check: An evaluation states both the intended benefit and the specific cost.
Practise and continue
Practise this
Explain why growing food demand and limited suitable land encourage intensive methods, then give one cost each of pesticide use and slash-and-burn.
Need a hint?
Keep the two environmental mechanisms distinct.
Check your answer
Answer: More food is needed from limited land. Pesticides can harm non-target organisms or enter food chains; slash-and-burn causes haze, deforestation and greater soil erosion.
Check: Name the method responsible for each effect.
Think like a scientist
Why does a downstream algae increase not by itself prove that one farm caused it?
Check the reasoning
Other nutrient sources, rainfall and water conditions could contribute, so upstream comparisons, repeated sampling and evidence about runoff are needed.
Remember: A plausible mechanism strengthens a claim but does not replace controlled evidence.
One-minute check
Trace fertiliser nutrients from a field to increased algae in a stream.
Describe the separate pathways from slash-and-burn to haze and soil erosion.
Correct this common mistake: “Fertiliser used on land cannot contaminate nearby water.”
Syllabus and review details
- SEC G1 Science 2027 · 2027
Content structure and syllabus content, PDF pages 8–17
Last reviewed: