3.4 Factors affecting photosynthesis

Question 1

EXAM QUESTION:

Give two factors which could be limiting the rate of photosynthesis in the sun plant between points A and B. (not LI) (2)

Answer 1

Temperature

Carbon dioxide

Question 2

EXAM QUESTION:

Suggest and explain why the rate of photosynthesis was low between 525nm and 575nm (2)

Answer 2

• less absorption of these wavelengths

- light required for light-dependent reaction/photolysis

Question 3

Define limiting factor

Answer 3

A factor that limits the rate at which a process can take place

Question 4

Define law of limiting factors

Answer 4

at any given moment, the rate of a physiological process, is limited by the factor that is at its least favourable value.

Question 5

Light intensity

When light is the limiting factor…?

Define compensation point (2)

Define light saturation point (2)

Answer 5

rate of photosynthesis is directionally proportional.

respiration = photosynthesis, no net exchange of gases.

light intensity no longer has effect on rate of photosynthesis, another factor is limiting

Question 6

Carbon dioxide

Optimum = ?

why is it often limiting under normal conditions?

How can higher yields be produced in greenhouses?

Affects?

Answer 6

Optimum = 0.1%.

Often limiting under normal conditions (only 0.04%)

Air in greenhouses can be enriched with more carbon dioxide for higher yields.

Enzyme that catalyses combination of carbon dioxide and RuBP in the light-independent reaction.

Question 7

Temperature

When temperature is the limiting factor….

0-25 degrees = ?
25 degrees = ?
Above 25 degrees = ?

Why does temperature not always affect photosynthesis?

Answer 7

rate of photosynthesis is directionally proportional

0-25 degrees = rate doubles every 10 degree rise
25 degrees = optimum temperature
Above 25 degrees = enzyme denaturation

because light-independent reaction is purely chemical.