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5.1Use of Biological Resources

Food Production — Edexcel Linear - OL Revision Notes & Topical Questions

10 min read 16 parts Lesson 4 of 8 Unit quiz

📚 Edexcel Linear - OL Hub / Topical Revision
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Lesson summary

Crop Production: Glasshouses, Limiting Factors, Fertilisers and Pest Control — EDEXCEL LINEAR - OL notes: Explain how farmers raise yields by controlling photosynthesis, adding mineral ions and controlling pests.Growing crops outdoors does not allow control of limiting factors.

  • Polythene tunnels
  • Worked example 1
  • Worked example 2
  • Worked example 3
  • Worked example 4
  • Polytunnel

Part 1 of 5Glasshouses and polythene tunnels

Growing crops outdoors does not allow control of limiting factors.

1
Enclosed environments let farmers raise the rate of photosynthesis.
2
In a glasshouse: heating (enzymes work faster at slightly higher temperature; used in temperate countries such as the UK), artificial lighting (longer photosynthesis), extra carbon dioxide,
  • and regular watering.
3
Farmers must balance the cost of heating, lighting and carbon dioxide against the extra income.
4
In hot countries glasshouses need ventilation so enzymes in photosynthesis do not denature.

Polythene tunnels (polytunnels) are large plastic covers that protect crops from wind, rain and extreme temperatures, raise the temperature slightly and keep out pests and diseases.

Explaining costs and benefits

  • extra yield from heated, lit glasshouses has to pay for fuel and electricity, so these methods suit high-value crops such as tomatoes.
  • Polytunnels are cheaper and protect against frost and rain but give less control.
  • Both methods let the farmer extend the growing season, so crops can be harvested earlier or later than outdoors.

Part 2 of 5Limiting factors of photosynthesis

With unlimited light, carbon dioxide, water and a warm temperature, the plant itself limits the rate. Usually one factor is in shortest supply, the limiting factor, and the rate cannot rise until it is increased. Three main factors:

FactorEffect
TemperatureRate rises with temperature (enzyme controlled) until the enzymes denature and the rate falls
Light intensityMore light, faster rate, until another factor becomes limiting
Carbon dioxideA raw material; more gives a faster rate until another factor limits

Reading graphson a rate against light intensity graph, the line rises then flattens.

Limiting factors of photosynthesis
The rising part shows light is limiting; the flat part shows another factor, such as carbon dioxide or temperature, is now limiting.
On a temperature graph the line rises, peaks at the optimum and then falls steeply as enzymes denature.
Always say what is limiting on each section of the graph.

Part 3 of 5Fertilisers

Fertilisers raise the amount of key nutrients in the soil so crops grow larger and healthier, increasing yield. Crops remove mineral ions, which must be replaced if crops are grown year after year. Organic fertilisers include manure and compost; chemical fertilisers are applied as granules or sprays.

Mineral ionFunctionDeficiency sign
MagnesiumNeeded for chlorophyllYellowing of leaves
NitrateNeeded for amino acids and proteinsWeak growth and yellow leaves
PhosphateATP, DNA, RNAPoor roots, purple-tinged leaves, stunted growth
CalciumCell walls and membranesDeformed new leaves, stunted growth
PotassiumOpening of stomataYellowing at leaf edges

Learn magnesium for chlorophyll and nitrate for amino acids. Spell nitrate correctly; plants need nitrate ions, not nitrites or nitrogen.

Part 4 of 5Pest control

Insects eat crops, weeds compete for space, water and nutrients, and fungi spread disease.

Pest control
Pesticides (insecticides, herbicides, fungicides) kill them quickly and are cheap,
  • but pests can become resistant, non-target organisms such as bees are killed, and persistent chemicals build up in food chains.
Biological control uses a natural predator, such as ladybirds eating aphids or parasitic wasps controlling whitefly in glasshouse tomatoes.
It is natural, long-lasting and specific,
  • but slow and never kills all the pests;
    • the introduced predator may eat other organisms or become a pest itself.

Part 5 of 5Worked examples

  1. Give three ways a farmer increases the rate of photosynthesis in a glasshouse. [3]3 marks

  2. Explain why a farmer in a hot country ventilates a glasshouse. [2]2 marks

  3. A crop has yellow leaves with weak growth. Which ion is likely missing and why? [2]2 marks

  4. Give an advantage and a disadvantage of biological control. [2]2 marks

Key terms

TermMeaning
Limiting factorFactor in shortest supply that restricts the rate of a process.
GlasshouseBuilding with controlled conditions for growing crops.
PolytunnelPlastic tunnel protecting crops.
FertiliserSubstance adding mineral ions to soil.
PesticideChemical that kills pests.
Biological controlUsing predators or parasites to control pests.

Avoid these mistakes

1
Writing nitrite or nitrogen for the ion plants absorb — it is nitrate.
2
Saying light is always limiting — whichever factor is lowest is limiting.
3
Thinking fertilisers feed plants directly — they provide mineral ions.
4
Believing pesticides are specific — most are non-specific.

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