Question

The specific function of light energy in the process of photosynthesis is to
A. Activate chlorophyll
B. Split water
C. Reduce carbon dioxide
D. Synthesize glucose

Answer 1

Hint: The photosynthesis takes place in the presence of sunlight in the thylakoid of chlorophyll where the plant absorbs carbon dioxide (${CO_2}$) and water to form food in the form of glucose. The absorbed water donated electrons for the initiation of the mechanism of photosynthesis.

Complete answer:
The initial stage of photosynthesis takes place by splitting of water, which is known as photolysis of water.
This step is called photolysis because the photon of the sunlight helps to break the water that is present inside the chlorophyll.
The photolysed water donate electrons and that electron is taken up by photosystem - II (PS II).
The photosystem II activates when 680 nm wavelength sunlight falls on it and with the electron it becomes activated and passes the electron to photosystem I (PS I) by some intermediate and the PS I finally passes the electron to NADH for its reduction.
The PS I get activated when 720 nm wavelength of sunlight falls on it.
This process is known as Z – Scheme.

So, here the correct answer is option B. Split water.

Note: The name of two herbicides should be remembered – DCMU and Paraquat. The former blocks the electron flow from PSII to PSI and the later blocks the electron flow from PS I to NADH. The full form of DCMU is 3-(3, 4 – dichlorophenyl) – 1, 1 – dimethylurea. You can also remember the common name of DCMU and that is Diuron.