factors affecting the rate of photosynthesis

Question 1

define the term ‘limiting factor’

Answer 1

• a limiting factor is a factor that is nearest to its minimum value, and directly increases the rate of reaction when its quantity is changed

Question 2

what are the 7 factors affecting the rate of photosynthesis?

Answer 2

1. light intensity
2. CO2 concentration
3. temperature
4. wavelength of light
5. oxygen concentration
6. availability of water
7. chlorophyll concentration

Question 3

how does light intensity affect the rate of photosynthesis?

Answer 3

• as light energy is required for photoactivation of special chlorophyll a & the photolysis of water in photophosphorylation,
• for the synthesis of NADPH & ATP for the Calvin Cycle,
• at low light intensities,

Question 4

explain why the rate of photosynthesis increased sharply when light intensity increases

Answer 4

• as light intensity is the limiting factor,
• when light intensity increases, more light energy is absorbed by photosynthetic pigments,
• the rate of photoactivation of special chlorophyll a & photolysis of water increases,
• causing the rate of the light dependent reaction, and in turn, photosynthesis, to increase

Question 5

explain why the rate of photosynthesis increases gradually, when light intensity is further increased

Answer 5

• other factors are now becoming the limiting factors

Question 6

explain why the rate of photosynthesis remains constant, even when light intensity increases

Answer 6

• the light saturation point is reached
• hence, light intensity is no longer a limiting factor, with other factors now becoming the limiting factors

Question 7

why is very high light intensity bad for plants?

Answer 7

• it can damage chlorophyll in the chloroplasts of the leaves, reducing the rate of photosynthesis

Question 8

what is a structural adaptation that plants developed to cope with very high light intensities?

Answer 8

• plants exposed to high light intensities (e.g. desert plants) usually have thick cuticles & hairy leaves

Question 9

define the term ‘compensation point’

Answer 9

• the compensation point is light intensity whereby the rate of photosynthesis equals the rate of respiration

Question 10

is there net gaseous exchange between the plant & its surroundings @ the compensation point?

Answer 10

• NO
• at the compensation point, all the CO2 produced during respiration is used in photosynthesis,
• while all the oxygen produced in photosynthesis is used in respiration
• hence, there is no net gaseous exchange