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A Handbook of Biology

Rate of photosynthesis

Light intensity

A

B

C

D

E



Light quality, light intensity and

duration

of

exposure

to

light

influences photosynthesis.



There is a linear relationship between

incident light and CO2 fixation rates

at low light intensities.



At higher light intensities, the rate

does not further show increase

because other factors become

limiting.



Light saturation occurs at 10% of the full sunlight. Hence, except for

plants in shade or in dense forests, light is rarely a limiting factor in

nature.



High increase in incident light breaks down chlorophyll which results

in decrease in the process of photosynthesis.

01

LÏGHT

02 ÇÅRBØÑ DÏØXÏDË ÇØÑÇËÑTRÅTÏØÑ



CO2 is the major limiting factor for photosynthesis.



CO2 concentration is very low in the atmosphere

(0.03 - 0.04%). Increase in concentration up to 0.05%

cause increase in CO2 fixation rates. Beyond this the

levels can become damaging over longer periods.



At low light, C3 and C4 plants do not respond to

high CO2. At high light, they show increased rate of

photosynthesis.



C4 plants show saturation at about 360 mlL^-1



C3 plants respond to increased CO2 concentration and saturation

is seen only beyond 450 mlL^-1. Thus, current availability of CO2 levels is

limiting to the C3 plants.



Due to response to higher CO2 concentration, C3

plants show increased photosynthesis and higher

productivity. This fact is used for some green house

crops (tomatoes, bell pepper etc). They are grown

in CO2 enriched atmosphere.