All the reactions from the reduction of CO2 to the formation of sugar are included in :–a)Light reactionb)Photolysisc)Dark reactiond)Hill reactionCorrect answer is option 'C'. Can you explain this answer?

Question

All the reactions from the reduction of CO2 to the formation of sugar are included in :&ndash;a)Light reactionb)Photolysisc)Dark reactiond)Hill reactionCorrect answer is option 'C'. Can you explain this answer?

Answer

Photosynthesis comprises of light phase and dark phase
during light phase reducing power and assimilatory power are synthesized which are used in dark phase to reduce Co2 to carbohydrates
the dark phase comprises of initial carboxylation reaction, reduction of phosphoglyceric acid to phosphoglyceraldehyde and synthesis of carbohydrate and regeneration of ribulose 1,5 diphosphate from phosphoglyceraldehyde

Answer

The dark reaction of photosynthesis is not dependent on sunlight but it does not mean it does not occur in its presence. The dark reaction occurs both in the presence and absence of sunlight. This reaction occurs in the stroma of the chloroplasts which are cell organelles known as the kitchen of the cells. The CO2 taken in by the plant combines a 5 carbon compound known as ribulose 1,5- biphosphate to form two molecules of 3-phosphoglycerate(3PGA). This step is catalyzed by the enzyme ribulose biphosphate carboxylase or RUBISCO(RuBp).

Answer

The overall process of reducing CO2 to the formation of sugar is known as photosynthesis. It involves a series of reactions that occur in the chloroplasts of plant cells. These reactions can be divided into two main stages: the light-dependent reactions and the light-independent reactions.

1. Light-Dependent Reactions:
- Absorption of light energy by chlorophyll molecules in the thylakoid membranes of chloroplasts.
- Conversion of light energy into chemical energy in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).
- Splitting of water molecules (photolysis) to release oxygen gas as a byproduct.
- Generation of ATP and NADPH, which will be used in the next stage.

2. Light-Independent Reactions (Calvin Cycle):
- Fixation of carbon dioxide (CO2) by the enzyme Rubisco (ribulose bisphosphate carboxylase/oxygenase) with the help of ATP and NADPH.
- Formation of an unstable 6-carbon compound, which immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA).
- Conversion of 3-PGA into glyceraldehyde-3-phosphate (G3P) through a series of reactions involving ATP and NADPH.
- Regeneration of the starting molecule (ribulose bisphosphate) for the CO2 fixation step using ATP.
- Conversion of G3P into glucose or other sugars, which can be used for energy production or stored for later use.

Overall, the reactions involved in the reduction of CO2 to sugar during photosynthesis are complex and require the input of light energy, water, and various enzymes and coenzymes. The process is vital for the synthesis of organic compounds in plants and plays a crucial role in the global carbon cycle and the production of oxygen.

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