Question

6CO2 + 6H2O + light energy -> C6H12O6 + 6O2 is the overall reaction of photosynthesis. In which of the photosynthetic reactions is carbon dioxide consumed?

1) the light reactions

2) the dark reactions

3) in both the light and dark reactions

4) in the Krebs cycle

Answer 1

CO_{​​​​​2} is consumedin the dark reaction.

Photosynthesis takes place in the green leaves.most active photosynthetic tissue in higher plants is the mesophyll of the leaves. Mesophyll leaves have many chloroplast, which contain specialised light absorbing green pigments called chlorophyll.

Chloroplasts:-

It is double membrane organelle ,which possess a third system of membranes called thylakoids.

A stack of thylakoids forms granum.Adjacent grana are connected by unstacked membranes called lamellae. The fluid compartment surrounding the thylakoids,called the stroma.

There is a clear division of labour within the chloroplast.

• Proteins and pigments(chlorophyll and carotenoids) that function in the photochemical events of photosynthesis that is trapping the light energy and synthesis of ATP and NADPH, are embedded in the thylakoid membrane.
• In stroma, enzymatic reactions incorporate CO_{​​​​​2} into the plant leading to the synthesis of sugar,which in turn forms the starch.

The former set of reactions are directly light driven and are called light reaction. The latter are not directly light driven but are dependent on the product of light reactions (ATP and NADPH) are called dark reactions.

It should not be understood that they occur in darkness or that they are not light driven.

Dark reaction occurs through Calvin cycle.

The primary acceptor of carbon dioxide during C_{​​​​​​3}  cycle is a five carbon ketose sugar- Ribulose bisphosphate (RuBP). The enzyme for carbon dioxide fixation is RuBisCO( Ribulose bisphosphate carboxylase oxygenase).

Krebs cycle is not a part of photosynthesis.

It is the subpart of aerobic respiration in plants