AQA GCSE Economics of enhancing the conditions in greenhouses (Biology)

Economics of enhancing the conditions in greenhouses

A quick recap of limiting factors:

A limiting factor is the factor in shortest supply.

The limiting factors for photosynthesis are

1. Temperature

2. Carbon dioxide concentration

3. Light intensity

4. Amount of chorophyll

Key points for limiting factors:

-Only one factor is limiting at a time

-Increasing a factor only increases the rate until another factor becomes limiting

-Rate eventually plateaus when a factor is no longer limiting

Greenhouses:

A greenhouse is a structure made of transparent material that traps heat and allows light in, providing controlled conditions for plant growth.

There are several ways that farmers can increase the rate of photosynthesis within a greenhouse.

Limiting Factor	How to increase the limiting factor	How this will affect costs
Light intensity	Artificial lighting	High electricity cost
Temperature	Electric or paraffin heaters	High electricity cost, or cost of paraffin
Carbon dioxide concentration	Paraffin heaters	Cost of paraffin

Increasing photosynthesis increases crop yield and the potential profit. However, there are additional costs to optimising the conditions for the limiting factors which will reduce profit.

Cost effectiveness

Farmers need to consider if changing environmental conditions will be cost effective.

It will be cost effective if the extra income from higher yield is greater than the cost of adding the additional environmental factor.

It is not cost effective if the rate of photosynthesis increases only slightly but costs a lot to change the environmental conditions.

For example in winter there is a low natural light intensity, so addition of artificial lights is likely to be cost effective as light is a limiting factor.

However, in summer when there is a high natural light intensity, addition of articifial lights is unlikely to be cost effective as light is probably not a limiting factor.

Heating when temperature is already near optimum temperature wastes money because the cost of heating is high.

Adding CO₂ only works if light intensity and temperature are not limiting.

Always remember, if you increase a limiting factor, the rate will only increase up to the point when another factor becomes limiting.

Data analysis.

Below is an example of a possible question.

Factor added	Increase in yield (%)	Cost per week (£)
Extra light	20	200
Heating	10	300
Carbon dioxide	15	100

Evaluate which factor is the most cost-effective to add to a greenhouse. Use the data.

Adding carbon dioxide is the most cost-effective option.

Carbon dioxide increases yield by 15% at a cost of £100 per week, which is cheaper than extra light (£200 for a 20% increase) and heating (£300 for only a 10% increase).

This suggests carbon dioxide is the limiting factor in the greenhouse. Increasing carbon dioxide increases the rate of photosynthesis, so yield increases significantly without high costs.

Heating is the least cost-effective because it gives the smallest increase in yield for the highest cost.

Practice Questions

1. If the light intensity is too high it can cause damage to the surface of a plant leaf. Suggest how plants could be protected within greenhouse from too much light intensity.

2. Use the following data to answer the next question.

Factor added	Increase in yield (%)	Cost per week (£)
Extra light	20	200
Heating	10	300
Carbon dioxide	15	100

Julie told her teacher, that she thought additional light would be the best way to increase the yield of crops because it gave the largest increase in yield. Explain why Julie may not be correct.