Question

First reaction in photosynthesis is
(A) Photolysis of water
(B) Excitation of chlorophyll molecules
(C) Formation of ATP
(D) Fixation of carbon dioxide

Answer 1

Hint: Green plants perform photosynthesis which is a physio-chemical process in which they use light energy to synthesis organic compounds. Green plants have pigment molecules which get excited first, in order to proceed further reactions.

Complete answer:
Plants perform photosynthesis in the green parts of the plant. The green colour is due to the pigment chlorophyll which is present in the organelle, chloroplast.
Chloroplast is a double membraned organelle, where two sets of reactions take place. They are light and dark reactions.
Light reaction – They are light driven reactions, where light is used for the photolysis of water and production of ATP and NADPH through phosphorylation reaction.
Dark reaction – They are not directly light driven, but they are dependent on products of light reaction.
Light reactions are otherwise known as photochemical phase involves the following process,
(i) Light absorption
(ii) Excitation of pigment molecules
(ii) Water splitting
(iii) Oxygen release
(iv) Formation of ATP and NADPH
Dark reaction or biochemical phase involves,
Fixation of carbon dioxide to produce glucose molecules.
Based on the above explanation, the given options can be written in the correct order,
(B) Excitation of chlorophyll molecules
(A) Photolysis of water
(C) Formation of ATP
(D) Fixation of carbon dioxide

Hence the correct answer is option(B)

Note: It is important to know the correct sequence of processes taking place in light and dark reactions. Moreover, dark reactions don’t mean they take place in the dark.