Question

The process of assimilation of $CO_2$, to produce carbohydrates is
A. Oxidation
B. Catabolic
C.Reductive
D. All of the above.

Answer 1

The assimilation of $CO_2$ is the process by which the atmospheric carbon is converted into carbon compounds such as carbohydrates in the process of photosynthesis.

Complete Answer:
- Photosynthesis is the process performed by autotrophic organisms. It is the mechanism through which an autotrophic organism is able to prepare food.
- Photosynthesis involves two reactions, light reaction, and dark reaction. Light reactions require light for the conversion of radiant energy into chemical energy.
- Dark reactions do not require light as dark reactions consist of a complex cycle which is enzymatically mediated reactions i.e. Calvin cycle.
- This reaction catalyzed the reduction of carbon dioxide to sugars. Reduced NADPH (nicotinamide adenine dinucleotide phosphate ) and ATP (adenosine triphosphate) are required for this cycle. NADPH and ATP are produced in light reactions and are utilized in dark reactions that are sensitive to light.

Therefore, the correct answer is option C. Reductive.

Additional information:
- $CO_2$ is a reduced form of carbohydrates and this is the basic mechanism of the Calvin cycle.
- The Calvin cycle is also known as the $C_3$ cycle as this cycle starts with three-carbon compounds. It was discovered by Melvin Calvin in Chlorella pyrenoidosa and Scenedesmus oblique. For this Calvin received a Nobel prize in 1961. $CO_2$ fixation is closely linked to the light reactions.
- During evolution, three different ecological variants that have been evolved with different $CO_2$ incorporation mechanisms are $C_3$, $C_4$, and CAM plants.

Note: Stroma of chloroplasts is the place where carbon dioxide fixation takes place.