Four statements are given below:
(i) PC is a copper containing mobile e carrier.
(ii) Chemiosmotic theory was given by Mitchell.
(iii) Photorespiration is feature of C4 plants.
(iv) PEPCO is the main photosynthetic enzyme of C3 plants.
Find set of correct statements.

Question

Four statements are given below: 
(i) PC is a copper containing mobile e carrier. 
(ii) Chemiosmotic theory was given by Mitchell. 
(iii) Photorespiration is feature of C4 plants. 
(iv) PEPCO is the main photosynthetic enzyme of C3 plants. 
Find set of correct statements.

Accepted Answer

The correct option is 1: (i), (ii)

The correct set of statements includes (i) and (ii), as both accurately reflect fundamental concepts in plant physiology and biochemistry. Statement (i) correctly identifies PC, or **Plastocyanin**, as a crucial component of the photosynthetic electron transport chain. Plastocyanin is a small, mobile protein located in the thylakoid lumen that acts as an electron carrier between the cytochrome b6f complex and Photosystem I. Its characteristic blue color is due to the presence of a single **copper atom** at its active site, which cycles between the cuprous (Cu+) and cupric (Cu2+) states, enabling it to efficiently transfer a single electron. Statement (ii) accurately credits the formulation of the **Chemiosmotic Theory** to the Nobel laureate **Peter Mitchell**. This groundbreaking theory, which he proposed in 1961, explains how the energy released from electron transport chains in both mitochondria and chloroplasts is converted into chemical energy (ATP). It posits that ATP synthesis is powered by an electrochemical gradient, known as the proton motive force, generated by pumping protons across a membrane, which then flow back through the ATP synthase enzyme.

The incorrect option is (i), (iv)

This option is incorrect because while statement (i) is correct, statement (iv) is factually inaccurate. Statement (iv) claims that PEPCO (Phosphoenolpyruvate carboxylase) is the main photosynthetic enzyme of C3 plants. This is false. In C3 plants, the main enzyme responsible for the primary fixation of atmospheric carbon dioxide into an organic molecule (Ribulose-1,5-bisphosphate) is **RuBisCO** (Ribulose-1,5-bisphosphate carboxylase/oxygenase). PEPCO is the primary CO2 fixing enzyme in C4 plants, where it efficiently fixes CO2 into a C4 acid in the mesophyll cells. While C3 plants may contain trace amounts of PEPCO, it plays no central role in the Calvin cycle, which is the main pathway for carbon assimilation.

The incorrect option is (ii), (iii)

This option is incorrect because while statement (ii) is correct, statement (iii) is profoundly misleading regarding the characteristics of C4 plants. Statement (iii) suggests that **photorespiration** is a feature of C4 plants. In reality, C4 plants, such as maize and sugarcane, have evolved a specialized leaf anatomy (Kranz anatomy) and a two-step CO2 fixation mechanism specifically to **minimize or completely suppress photorespiration**. By concentrating carbon dioxide in the bundle-sheath cells where the Calvin cycle occurs, the C4 pathway ensures that RuBisCO primarily functions as a carboxylase, thus avoiding the wasteful oxygenase activity that defines photorespiration. Photorespiration is, instead, a key and costly characteristic of C3 plants, especially in hot, dry conditions.

The incorrect option is (iii), (iv)

This option is incorrect because both statement (iii) and statement (iv) are factually incorrect. As established, statement (iii) falsely attributes photorespiration as a feature of C4 plants, when their entire evolutionary advantage is based on its suppression. Similarly, statement (iv) incorrectly identifies PEPCO as the main photosynthetic enzyme of C3 plants; this role belongs exclusively to RuBisCO. The correct set of features for these pathways are: C3 plants have RuBisCO as the main enzyme and high photorespiration, while C4 plants use PEPCO for initial fixation, RuBisCO for final fixation, and have virtually no photorespiration. Therefore, a combination built on two erroneous statements cannot be the correct answer.