BOTANY Higher Secondary Second Year - Textbooks Online

Glycine molecules enter into mitochondria where two molecules of
glycine combine to give a molecule of serine, NH 3 and CO 2. During this
process, NAD + is reduced to NADH 2.
The aminoacid serine is taken to peroxisome where, it is converted
into hydroxy pyruvic acid. Hydroxy pyruvic acid is reduced by NADH 2
to form glyceric acid.
The glyceric acid leaves peroxisome and enters chloroplast, where it
is phosphorylated to PGA, which enters into Calvin cycle. During the
photorespiratory pathway, one CO 2 molecule released in mitochondria is
to be re-fixed.
Photorespiration is also known as photosynthetic carbon oxidation
cycle or C 2 cycle. Under the conditions of high light and limited CO 2
supply, photorespiration protects the plants from photooxidative damage.
This means that, if enough CO 2 is not available to utilize light energy,
excess energy causes damage to plant. However, photorespiration utilizes
part of the light energy and saves the plant from photooxidative damage.
Increased O 2 level increases photorespiration whereas increased CO 2 level
decreases photorespiration and increases photosynthesis.
Difference between photorespiration and dark respiration
Photorespiration Dark respiration
1. It takes place only in photo - It takes place in all living cells in the
synthetic cells in the presence mitochondria.
of light.
2. It is light dependent It takes place in the presence and
in the absence of light.
3. It is the function of chloroplast, It is the function of mitochondria
peroxisomes and mitochondria. alone.
5.2.8. Factors affecting photosynthesis
Photosynthesis is influenced by both environmental and genetic factors.
The environmental factors include light, availability of CO 2 , temperature,
soil, water and nutrient supply apart from age of leaf, leaf angle and leaf
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