Question

Write the short notes on $C_4$ and $C_3$ plant.

Answer 1

C3 PLANTS:

$C_3$ plants are the plants in which fixation of carbon dioxide occurs through Calvin cycle or $C_3$ pathway because the first stable product which is formed after fixation of carbon dioxide is a three-carbon compound Phosphoglyceric Acid (PGA). $C_3$ pathway is the major pathway for the fixation of carbon dioxide in plants and it represents phase-II i.e. the dark reaction part of photosynthesis.

$C_3$ plants also show photorespiration in which the enzyme RuBisCO in presence of high Oxygen concentration binds with $O_2$ instead of $C{O}_2$ and forms a molecule of phosphoglycerate and phosphoglycolate. There is neither synthesis of sugars nor the ATP and so it is a wasteful process because it releases $C{O}_2$ and also utilizes ATP.

$C_4$ PLANTS:

$C_4$ plants are the plants in which the first stable product formed after fixation of carbon dioxide is a four-carbon compound Oxaloacetic acid (OAA)

$C_4$ plants have a characteristic anatomy:

1.Leaf mesophyll cells are compactly arranged

2. Mesophyll cells are not differentiated into palisade and spongy mesophyll.

3. The vascular bundles in the leaves are surrounded by a layer of radially enlarged parenchyma cells called bundle sheath cells.

4. Chloroplasts are dimorphic:

Mesophyll cells have smaller chloroplasts and possess grana.

Bundle sheath cells have larger chloroplasts and are without grana.

This type of anatomy of $C_4$ plants is called Kranz anatomy.