Question

Which of the following is concerned with carbon dioxide fixation?
A. Kreb’s cycle
B. Calvin cycle
C. Ornithine cycle
D. Glycolysis

Answer 1

Hint: Carbon dioxide fixation or carbon assimilation is the process in which the organic carbon is formed from the inorganic carbon by living organisms. These carbon compounds are then used to store energy and building blocks for other biomolecules.

Complete answer:
The process of carbon dioxide fixation is very important as the most prominent example of carbon dioxide is photosynthesis which occurs in plants in presence of sunlight and chemosynthesis that occurs in absence of sunlight. The organisms that prepare their own food by fixing carbon are called autotrophs, which include photoautotrophs and lithoautotrophs. Heterotrophs consume the carbon fixed by autotrophs to fulfill their energy needs.
Calvin cycle explains the whole biosynthetic pathway that occurs in all photosynthetic plants. It explains the chemical reactions that convert carbon dioxide and other compounds into glucose. These chemical reactions take place in the stroma of chloroplast in photosynthetic plants. The Calvin cycle uses the energy from electronically excited carriers to convert carbon dioxide and water into organic compounds. The key enzyme that facilitates this reaction is called RuBisCo. This reaction helps in carbon fixation which helps to make food in photoautotrophs. The enzyme is activated in the presence of the light and reactions are light-dependent reactions. These regulatory functions prevent the Calvin cycle from being respired to carbon dioxide which would waste energy in carrying out reactions.

Hence, the correct option is B. Calvin cycle.

Note: The first stable product discovered was 3-phosphoglyceric acid (PGA). Calvin cycle occurs in three stages which are carboxylation, reduction, and regeneration.