Question

Photolysis of water is caused by
a. PS-1
b. PS-2
c. PS-1 and PS-2
d. None of the above

Answer 1

Hint: The photolysis of water molecules takes place on the inner side of the membrane and the hydrogen ions (protons) are produced, these water molecules accumulate within the lumen of the thylakoids.

Complete answer:
The water splitting complex is associated with the PS 2, which is permanently located on the inner side of the membrane of the thylakoid. Water is split into hydrogen ion, oxygen ion and electrons. The protons and oxygen formed by the splitting of water is released within the lumen of the thylakoid.

Photolysis of water is the splitting of water molecules into hydrogen and oxygen in the presence of sunlight. During the process of photosynthesis, photosystem 2 absorbs the light energy. The electrons are energized to the excited state and absorbed by the electron acceptor. When the electron reaches the ground state, due to the presence of photons the splitting of water molecules takes place.

Photosystem 1 and photosystem 2 are the group of pigment molecules which take part in the conversion of light energy into the chemical energy. These are also known as photosynthetic units. Each unit has a reaction centre which absorbs the light energy of longer wavelength.

In PS-1, the reaction centre chlorophyll a, has an absorption peak at 700 nm, hence it is called P700 whereas in PS-2, reaction centre has an absorption peak at 680 nm and it is known as P680.

Hence, the correct answer is option (B).

Note: Light harvesting complex helps to make photosynthesis more efficient by absorbing different wavelengths of light. Both red and blue light are equally effective in photosynthesis but red light is more efficient.