Question

What is $C_2$ Cycle?
A) Glyoxylate cycle
B) Calvin cycle
C) Krebs cycle
D) TCA cycle

Answer 1

It is often called the cycle of $C_2$, since a two-carbon compound is the first stable substance i.e., phosphoglycolic acid. This process occurs in chloroplast, peroxisomes and mitochondria.

Complete answer:
First we should know about photosynthesis in higher plants to answer this question. Everyone is sure of the fundamentals of photosynthesis. Photosynthesis requires additional steps in higher plants, but it remains essentially the same. It is a physicochemical method that utilises sunlight for organic compound synthesis. Oxygen is emitted into the environment in this process. The following mechanisms are involved in photosynthesis in higher plants: Light reaction and Dark reaction
Now, let us find the solution from the options-

Photorespiration is an unnecessary process that results in the depletion of carbon dioxide which was fixed by plants. It happens as a result of the oxygenase production of the enzyme RuBisCo present in $C_3$ plants. In chloroplasts, peroxisomes and mitochondria, this process exists. The first stable result of the photorespiration reaction is a 2 carbon compound called glycolate, so the photorespiration is also called the $C_2$ cycle or glycolate metabolism.
The Calvin cycle is known as the $C_3$ cycle, since a three-carbon compound is the first stable substance (phosphoglyceric acid). Thus, the option B is incorrect.
Synonyms include the Krebs cycle and the TCA cycle. The Krebs cycle is called the TCA cycle, since there are three carboxylic groups in the first stable product (citric acid). Hence the name of the cycle of tricarboxylic acid. Thus, the options C and D are incorrect.

Thus, the correct answer is option ‘A’ i.e, Glyoxylate cycle.

Note: Phosphoglycolate becomes glycolate by phosphate depletion. In chloroplast glycolate forms and joins the peroxisome to form glyoxylate and hydrogen peroxide. Glyoxylate is translated into glycine and moved into mitochondria. Two molecules of glycine bind to form serine in the mitochondria. To form hydroxy pyruvate, serine joins the peroxisome.