Question

Compare and contrast photosystem 1 and photosystem 2. Please be at least 7 sentences and be descriptive about each and every difference and similarity.

Answer 1

• The multi-protein complexes photosystem I and photosystem II contain the pigments necessary to harvest photons and use light energy to catalyse the primary photosynthetic endergonic reactions producing high energy compounds.
• Photosystem I and II are highly organised membrane super-complexes composed of a core complex, containing the reaction center where electron transport is initiated, and of a peripheral antenna system, which is important for light harvesting and photosynthetic activity regulation.
• Photosystem I is located at the outer surface of the grana thylakoid membrane, whereas photosystem II is located at the inner surface of the grana thylakoid membrane.
• Photosystem II has a quinone type reaction center (Q-Type or type II), while photosystem I has an iron-sulphur (FeS) type reaction center (type I).
• The core complex of photosystem I is composed of 15 subunits of proteins, whereas the photosystem II is composed of 25 to 30 subunits.
• Pigments of photosystem I absorb longer wavelength of light thta is greater than 680nm, while the pigments of photosystem II absorb shorter wavelength of light that is smaller than 680nm.
• Photosystem I is rich in chlorphyll a and photosystem II is rich in chlorophyll b.
• Photosystem I participates in cyclic and non-cyclic phosphorylation, whereas photosystem II participates only in non-cyclic phosphorylation.
• In photosystem I ATP is syntesized in cyclic photophosphorylation and NADPH is synthesized in non-cyclic photophosphorylation. In photosystem II, ATP is synthesized and water is hydrolyzed.
  Photolysis of water takes place in photosystem I whereeas in photosystem II photolysis of water does not take place.
• The photocenter of phosystem I is P700 and the photocenter of photosystem II is P680.