Question

The $C_4$ plants are different from the $C_3$ plants with reference to the

• A. Types of pigments involved in photosynthesis.
• B. The number of NADPH that are consumed.
• C. End product.
• D. The substance that accepts $C{O}_2$ in carbon assimilation and first stable product.

Answer 1

The correct option is D The substance that accepts $C{O}_2$ in carbon assimilation and first stable product.

The $C_4$ plants are so called because the first stable product of this process are the four carbon atom containing organic acids like oxaloacetic acid and malic acid. The initial acceptor of carbon dioxide is phosphoenol pyruvic acid (PEP) and the initial carboxylating enzyme is PEP carboxylase. The initial carboxylation reaction occurs in the mesophyll cells. The $C_4$ organic acids are decarboxylated in the bundle sheath cells to release carbon dioxide. In the bundle sheath cells the carbon dioxide is fixed with the help of ribulose 1,5 bis phosphate carboxylase oxygenase (RuBisCO) enzyme.
The $C_3$ plants are called so because, in these plants the first stable product of photosynthesis is the three carbon atom containing compound 3-Phosphoglyceric acid (3-PGA). The initial carbon dioxide acceptor is Ribulose-1,5-bisphosphate and the carboxylating enzyme is RuBisCO.