AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
(HT only) Limiting factors are important in the economics of enhancing the…
Full specification wording
Rate of photosynthesis: (HT only) Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit.
Growers can raise the rate of photosynthesis in greenhouses by adding artificial light, heating, or enriching the air with carbon dioxide.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 6 of 9
Study notes
From the checked teaching notes for this specification point.
The idea
Growers can raise the rate of photosynthesis in greenhouses by adding artificial light, heating, or enriching the air with carbon dioxide. Each enhancement costs money, so the aim is to increase growth and yield enough to cover those costs and still make a profit. The limiting factor idea guides decisions: if light is limiting, adding more carbon dioxide will not help until light is increased. Once one factor is no longer limiting, another factor takes over, so spending more on the first factor gives diminishing returns. For example, heating a greenhouse may speed growth in winter, but if light intensity is low, the extra heat may not raise the rate much. A grower compares the cost of each enhancement with the extra income from the improved yield, and stops adding a factor when the extra cost exceeds the extra income.
What earns the marks
- Identify ways greenhouse conditions can be enhanced, such as artificial lighting, heating and carbon dioxide enrichment.
- Explain that each enhancement has a cost that must be balanced against increased yield and income.
- Use limiting factor reasoning to show that adding a non-limiting factor does not increase the rate.
- Describe diminishing returns when a factor stops being limiting.
- Evaluate a commercial decision by comparing the cost of an enhancement with the value of the extra growth.
- Recognise that maximum profit may occur before the maximum possible rate of photosynthesis is reached.
Common mistakes and how to put them right
Assuming the maximum rate always gives maximum profit.
Put it right by comparing costs with income.
Adding more of a factor that is not limiting and expecting a higher rate.
Put it right by identifying the actual limiting factor first.
Ignoring running costs such as electricity or fuel.
Put it right by including them in the comparison.
Exam tips
- Name the limiting factor before suggesting a change to greenhouse conditions.
- Use comparative language such as greater than or less than when discussing cost and income.
- Link each enhancement to a specific effect on the rate of photosynthesis.
Try the lesson
The start of the Rate of photosynthesis: (HT only) Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit. lesson, made from checked teaching notes for this specification point.
Have a go first
A greenhouse grower can raise the carbon dioxide concentration or raise the temperature. Why does the grower need to know which factor is limiting the rate of photosynthesis before spending money on either change?
Listen
Growers can raise the rate of photosynthesis in greenhouses by adding artificial light, heating, or enriching the air with carbon dioxide. Each enhancement costs money, so the aim is to increase growth and yield enough to cover those costs and still make a profit. The limiting factor idea guides decisions: if light is limiting, adding more carbon dioxide will not help until light is increased. Once one factor is no longer limiting, another factor takes over, so spending more on the first factor gives diminishing returns. For example, heating a greenhouse may speed growth in winter, but if light intensity is low, the extra heat may not raise the rate much. A grower compares the cost of each enhancement with the extra income from the improved yield, and stops adding a factor when the extra cost exceeds the extra income. A strong answer earns marks for these points. Identify ways greenhouse conditions can be enhanced, such as artificial lighting, heating and carbon dioxide enrichment. Explain that each enhancement has a cost that must be balanced against increased yield and income. Use limiting factor reasoning to show that adding a non-limiting factor does not increase the rate. Describe diminishing returns when a factor stops being limiting. A common slip: Assuming the maximum rate always gives maximum profit. Instead, comparing costs with income. Exam tip: Name the limiting factor before suggesting a change to greenhouse conditions.
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