Page 15 - 9-BIO-7

7. Bioenergetics eLearn.Punjab

Photosynthetic pigments are organized in the form of
clusters, called photosystems, in thylakoid membranes
of chloroplasts. Chlorophyll-a is the main photosynthetic
pigment. Others are called accessory pigments and include
chlorophyll-b and carotenoids. Chlorophylls absorb mainly
blue and red lights. Some wavelengths not absorbed by
chlorophyll ‘a’ are very effectively absorbed by accessory
pigments and vice-versa.

Calvin was awarded Nobel prize, inWater
1961, for his work on the details of
photosynthesis.

In dark reactions, 3-carbon compounds are reduced to form carbohydrates.
What is the ultimate source of these hydrogen for this reduction?

7.2.3 Limiting Factors In Photosynthesis

Any environmental factor the absence or deficiency of which can decrease the rate of a metabolic
reaction, is called limiting factor for that reaction. Many factors like light intensity, temperature,
concentration of carbon dioxide and availability of water act as limiting factors for photosynthesis.

Effect of light intensity and temperature

The rate of photosynthesis varies with light intensity. It decreases as light intensity decreases and
increases as intensity increases. However at much higher light intensity, the rate of photosynthesis
becomes constant.

15 V: 1.1