1. Factors Affecting Rate of Photosynthesis

2. Let’s Recall… What are the factors required for photosynthesis?
How do we know if photosynthesis has been carried out by a plant?
How can we test for starch in a plant?
The main steps to test for starch in a leaf

3. Aims of Today’s Lesson
At the end of this lesson, you should be able to
Investigate and discuss the effects of some factors on rate of photosynthesis
Discuss some factors affecting rate of photosynthesis as limiting factors
Describe and identify compensation point in a given graph plot

4. Back to the drawing board…
Chlorophyll
What other factors affect photosynthesis?
So, why is there a need to study the effects of these factors on the rate of photosynthesis in plants?
How can we measure the rate of photosynthesis?

5. Investigating Rate of Photosynthesis
2. Temperature
Vary from 5 to 75 °C
1. Light Intensity
Vary position of light source
Vary the watts
3. Carbon Dioxide
Vary conc. of NaHCO3 solution (e.g. 0.01M to 0.1M)

6. Light Intensity & Temp. constant Light Intensity &[CO2] constant
Dose-Response Plots
e.g. Rate of photosynthesis = Rate of bubbling (no. of bubbles per 5 mins)
[CO2] & Temp. constant
Light Intensity & Temp. constant
Light Intensity &[CO2] constant

7. How does it affect the rate of photosynthesis of plants on Earth?
Global Warming
Gradual increase in global temperature and CO2 emission
How does it affect the rate of photosynthesis of plants on Earth?
Atmospheric CO2

8. How does it affect the rate of photosynthesis of plants on Earth?
Global Warming
How does it affect the rate of photosynthesis of plants on Earth?

9. Light Spectrum & Photosynthesis
Chlorophyll absorbs different wavelengths of light during photosynthesis
Study on how different wavelengths of light affect rate of photosynthesis
Absorption vs. action spectrum
Can you explain why chlorophyll is green?
What colours of light are best?

10. Quick Review
What evidence on the graph indicates that chlorophyll is not the only pigment involved in photosynthesis?

11. What other external factors can you think of which affects the rate of photosynthesis in plants directly or indirectly?

12. Imagine this…..
I am sure you might have had days where you were too busy to have lunch and by the time its 2 pm, you become very hungry.
So knowing this, you are brought to an ‘all-you-can-eat’ buffet, and you are given the freedom to eat all you want.
Do you think you can finish the wide-spread buffet, every single morsel of it?
If you feel that you cannot, why do you think that is the case?

13. Limiting Factors What is a limiting factor?
A factor that directly affects a process if its quantity is changed
Rate of photosynthesis can be affected by a few limiting factors

14. Limiting Factors in Photosynthesis
Light intensity
Concentration of CO2
Temperature

15. Identifying Limiting Factor
Different graphs explaining the role of different limiting factors

16. Question 1
Ans: C

17. Question 2
Ans: B

18. Rate of Photosynthesis
Compensation Point
It is where, at a certain light intensity…
Rate of Photosynthesis
Rate of Respiration =
Amount of
CO2 used
Amount of
CO2 produced =
Amount of
O2 produced
Amount of
O2 used =

19. Compensation Point

20. Compensation Point (more example)

21. Compensation Point C D Net Gaseous Exchange A B
As light intensity increases, the rate of photosynthesis increases.
In region A, as light intensity is low, the photosynthetic rate is lower than respiratory rate.
At point C, respiratory rate = photosynthetic rate. Also known as the compensation point. There is no net gaseous exchange with the atmosphere outside the plant.
In region B, as light intensity is high, the photosynthetic rate is higher than respiratory rate.
After point D, the rate of photosynthesis reaches a maximum and stays unchanged despite of further increases in light intensity, as light is no longer the limiting factor. Other factors are limiting, e.g. temperature, CO2 concentration.

22. Question 3
Ans: C

23. Question 4
Ans: A

24. Question 5
Ans: A

25. Review
What is the factor which is limiting the rate of photosynthesis at point X on the graph?
Account for the increase in the rate of photosynthesis in graph 1 when the temperature is raised from 20 °C to 30 °C.
Name an environmental factor other than temperature which may be limiting the rate at point Y.

26. Summary What is a limiting factor?
What are the three main limiting factors in photosynthesis?
How does light intensity, CO2 and temperature affects the rate of photosynthesis
What is a compensation point?
Which colour of the light spectrum will plants grow worst in?