Question

In C$_3$ plants, the first stable product of photosynthesis during the dark reaction is
A. 3-phosphoglyceric acid
B. Phosphoglyceraldehyde
C. Malic acid
D. Ocalocaetic acid

Answer 1

Hint: Plant performs photosynthesis in two different phases such as the light-dependent reaction phase and light-independent reaction phase. In both phases different reaction enzymes are used and for the different cycle.

Complete answer: Plants have categorized into different photosynthetic cycle formation that name as C$_3$ cycle (Calvin cycle), C$_4$ cycle, and CAM cycle which occurs in different plant groups. C$_3$ cycle occurs in every plant, either plant is C$_4$ or C$_3$ cycle categorized.
C$_3$ cycle is light-independent photosynthesis and active when NADPH and ATP are abundant. The ATP provided by cyclic and non-cyclic photophosphorylation, which process the endergonic reaction. It is a three-step process named carbon fixation, reduction, and then regeneration. In the C$_3$ cycle, the first stable carbon compound formed during the reaction is 3-phosphoglyceric acid, which is a 3-carbon compound, which is called the C$_3$ pathway. C$_4$ the cycle occurs in many kinds of grass, monocot, and dicot plants, it is also a carbon fixation process, in this first stable carbon compound is formed is called oxaloacetic acid (OAA), which is a four-carbon compound. This cycle initiates with phosphoenolpyruvate (PEP), which is a 3-carbon compound. Malic acid is the organic compound that provides a sour taste and it is an intermediate product used in the C$_4$ cycle which is converted into pyruvic acid by reacting with NADP+. Phosphoglyceraldehyde is the carbon compound that is formed during the anaerobic metabolism of carbohydrates by breaking diphosphate fructose.
Hence the correct option is A.

Note: Apart from C$_3$ and C$_4$ cycle, CAM cycle also found in some plant that is called xerophytes or desert plants. CAM is called Crassulacean acid metabolism, which performs double fixation of carbon dioxide. Normally CAM plants perform C$_3$ plants but under stress, condition the plant performs the CAM process.