Question

Which among the following is a $C_3$ plant?

• A. Maize plant
• B. Sugarcane
• C. Soybean
• D. Millet plants

Answer 1

The correct option is C Soybean

Soybean is a $C_3$ plant. In $C_3$ plants, the primary acceptor of carbon dioxide is a 5 carbon compound, RuBP (ribulose-1,5-bisphosphate). RuBP combines with carbon dioxide and forms into an unstable 6 carbon compound which splits into two molecules of 3-PGA (3-phosphoglycerate). The first stable product formed in $C_3$ plants is 3-PGA, which is a 3 carbon compound. Hence, these plants are called $C_3$ plants.

Maize, sugarcane and millets are C${}_4$ plants. The primary acceptor of carbon dioxide in C${}_4$ plants is a 3 carbon compound, phosphoenol pyruvate (PEP). PEP combines with CO${}_2$ and forms oxaloacetic acid (OAA), which is a 4 carbon compound and hence these plants are called C${}_4$ plants.