Name: Light and the Dark Reactions of Photosynthesis
Uploaded: 2019-07-19
Duration: 4 min 38 s
Description: A big plan is to show all the reactions involved in photosynthesis, the light reactions as well as the dark reactions leading to the synthesis of carbohydrates.

Question

Describe the basic characteristics of a photosystem and explain how photosystem-I is different from photosystem-II.

Accepted Answer

The photosynthetic pigments in the higher plants are chlorophyll-a, chlorophyll-b, xanthophyll and carotenoids. These are organised into discrete light-harvesting complexes (LHC) called photosystems. The photosystems are made up of hundreds of pigment molecules bounded by protein. Photosystem is the functional unit of photosynthesis. Each photosystem has a reaction centre that contains a special chlorophyll-a molecule. It is fed by hundreds of other pigment molecules such as chlorophyll-b, chlorophyll-a, xanthophyll and carotenoids. It forms the light-harvesting system called antenna. The antenna complex absorbs light of different wavelengths, shorter than reaction centre and transfer it to the reaction centre. Based on the reaction centre, two types of photosystems are there: photosystem-I (PS-I) and photosystem-II (PS-II).

The major differences between PS I and PS II are the following:

Feature PS I PS II

Reaction centre Reaction centre is P₇₀₀, i.e., it absorbs 700nm wavelength of light. It is P₆₈₀ that absorbs 680nm wavelength of light.

Feature PS I PS II

Location It is situated on the outer surface of the thylakoid membrane and stroma lamellae. It is found on the surface of the thylakoid membrane only.

Feature PS I PS II

Function It is involved in both cyclic and non-cyclic photophosphorylation. It involves in noncyclic photophosphorylation only in which both ATP and NADPH₂ are formed.

Describe the basic characteristics of a photosystem and explain how photosystem-I is different from photosystem-II.

Important Questions on Photosynthesis in Higher Plants

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