Question

The first step in photosynthesis is

• A. joining of three carbon atoms to form glucose
• B. formation of ATP
• C. ionization of water
• D. excitement of an electron of chlorophyll by a photon of light

Answer 1

The correct option is D excitement of an electron of chlorophyll by a photon of light

Photosynthesis can be broadly studied under 2 categories- Light dependent reactions and Light independent reactions.

Light dependent reactions start when PS I absorbs light of wavelength 700nm, its electron in its reaction centre P700 chlorophyll a molecule gets excited and is expelled out which is received by a modified chlorophyll molecule $A_0$,$A_1$ , Fe-S centre, ferredoxin (Fd) and finally to ferredoxin ${\mathrm{NADP}}^{+}$ reductase (FNR) which passes on the electron to ${\mathrm{NADP}}^{+}$ which gets converted to NADPH.

When PS II receives a light of wavelength 680nm, the electron in its reaction centre P680 chlorophyll a molecule gets excited. It passes through a series of electron carriers namely phaeophytin, plastoquinone (PQ), cytochrome b-f complex and plastocyanin.

The electron loses an adequate amount of energy while passing over the cytochrome complex. This energy is used in the synthesis of ATP. The electron is then passed onto PS I.