Question

The graphs below show the amount of ATP and NADPH in isolated chloroplasts once these organelles are given light, and then later, after exposure to a herbicide. Based on the evidence presented in the graphs, it can be concluded that this herbicide affects photosynthesis by:

• A. Altering the movement of H${}^{+}$ across membranes of mitochondria
• B. Altering the movement of H${}^{+}$ across membranes of chloroplasts
• C. Inhibiting the reduction of NADP${}^{+}$
• D. Inhibiting the oxidation of NADH

Answer 1

The correct option is C Inhibiting the reduction of NADP${}^{+}$

Here, graph–1 for ATP shows that this herbicide is not altering the movement of H${}^{+}$ across the membrane of chloroplast (not mitochondria, as this process is going on in chloroplast) as even after addition of herbicide ATP synthesis remains the same.

Graph–2 for NADPH synthesis, predicts that as we added herbicide, the NADPH production falls down. It means the reduction of NADP${}^{+}\to$ NADPH was inhibited travelling the electrons in the chloroplast and thats how the electron transport chain to reduce NADP${}^{+}$ becomes blocked. So it can be concluded that this herbicide affects photosynthesis by inhibiting the reduction of NADP${}^{+}$.