Factors That Affect The Rate Of Photosynthesis
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of photosynthesis.
What are the reactants in photosynthesis?
Carbon dioxide and water
What are the products of photosynthesis?
Glucose and oxygen
What is the chemical formula for glucose?
C₆H₁₂O₆
Topic Explainer Videos
Check out these @lauradoesbiology and @JoeDoesBiology videos that explain factors that affect the rate of photosynthesis, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Factors Affecting the Rate of Photosynthesis
What is a Limiting Factor?
A limiting factor is something that if increased, would increase the rate of photosynthesis. If any one of the factors required for photosynthesis is limited, the process can’t go faster, no matter how much of the other factors are available.
Key limiting factors
- Temperature
- Light intensity
- Carbon dioxide concentration
Temperature
- Effect:
- As temperature increases, the rate of photosynthesis increases (due to more kinetic energy and more collisions between enzymes and substrates).
- If temperature gets too high (above ~45°C), enzymes denature, and the rate of photosynthesis decreases sharply.
- Manipulation:
- In greenhouses, heaters can maintain an optimum temperature for enzyme activity, especially in cooler climates.
Light Intensity
- Effect:
- More light = more energy for photosynthesis = faster rate.
- At a certain point, the rate levels off, if another factor becomes limiting.
- Manipulation:
Farmers use artificial lighting in greenhouses to extend daylight hours and increase productivity of crop plants.
Carbon Dioxide (CO₂) Concentration
- Effect:
- CO₂ is a reactant needed for photosynthesis.
- More CO₂ = faster rate, until another factor becomes limiting.
- Manipulation:
CO₂ can be added to greenhouses using paraffin heaters, which release CO₂ when they burn.
Interpreting rate of photosynthesis graphs
Higher tier only
Using Limiting Factors to Increase Yield
- Greenhouse conditions can be carefully controlled:
- Temperature: kept at optimum for enzymes.
- Light: extended using artificial lights.
- CO₂: added to boost photosynthesis.
- This increases the rate of photosynthesis, so plants grow faster, leading to higher crop yields.
Running heaters and artificial lights consumes a lot of electricity or fuel.
- This can lead to increased carbon emissions which contribute to the greenhouse effect.
Installation and maintenance of heating systems, lighting, and CO₂ enrichment equipment can be very expensive.
- There’s a point at which increasing light, CO₂, or heat no longer significantly improves yield.
- Beyond this point, the extra investment may not lead to enough profit to justify the cost.
Key Terms & Definition
|
Term |
Definition |
|---|---|
|
Limiting factor |
A factor that when increased, will increase the rate of a reaction. |
|
Light intensity |
The amount of light energy per unit of area. |
|
Optimum temperature |
The temperature at which photosynthesis happens at the fastest rate due to enzyme activity being at its maximum. |
|
Yield |
The amount of crop that is produced. |
No answer provided.
Exam Tip
In graph questions, make sure you can identify where the rate of photosynthesis plateaus (remains constant). This is where another factor becomes limiting - give an example of which factor may now be the limiting factor.
No answer provided.
Practice Question
Explain how three environmental factors can be controlled in a greenhouse to increase the rate of photosynthesis. (6 marks)
Model Answer:
- Temperature can be increased using heaters to keep enzymes working at their optimum (1).
- Light intensity can be increased by using artificial lights so photosynthesis can continue for longer hours (1).
- Carbon dioxide concentration can be increased by using paraffin heaters which release CO₂ when burned (1).
- Increasing temperature speeds up enzyme reactions involved in photosynthesis (1).
- Increasing light intensity gives more energy for photosynthesis (1).
- More CO₂ means more reactant is available for glucose production (1).
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!