Question

Photooxidation is
(a)Photorespiration
(b)Photolysis
(c)Light and oxygen-induced breakdown
(d)All of the above

Answer 1

Hint: Release of electrons from chlorophyll (PSII/P680) after absorption of a photon is known as photo-oxidation in chlorophyll. It generally occurs during non-cyclic photophosphorylation.

Complete answer:
The light‐dependent generation of active species of oxygen is termed photooxidative stress. This occurs in two ways:
 (1) the donation of energy or electrons to oxygen as a result of photosynthetic activity.
 (2) exposure of tissues to ultraviolet radiation.
During the process of photosynthesis, the formation of active oxygen species is minimized by a number of complex and refined regulatory mechanisms. During their production, active oxygen species are eliminated rapidly by efficient antioxidative systems. The chloroplast which involves functions such as production and destruction of hydrogen peroxide helps to regulate the thermal dissipation of excess excitation energy. This is an intrinsic feature of photosynthetic electron transport regulation.

Additional information:
During photolysis or photooxidation, an oxidized chlorophyll molecule takes away a replacement electron from water, which breaks to release oxygen. This generally occurs in the grana that is the lumen side of the thylakoid membrane with the help of water splitting complex also known as OEC (oxygen-evolving complex). This is a complex step and is associated with PS- II of the Z- scheme.
Active oxygen species constitutes the alarm-signaling processes in plants. These mainly serve to modify the metabolism and gene expression so that the plant can respond to adverse environmental conditions, invading organisms, and ultraviolet radiation. The efficiency of the antioxidative defense system increases at such duration but if the response is less then radical production will exceed scavenging and ultimately lead to the disruption of the metabolism process. Oxidative damage may arise due to high energy light generally when the latter is in synergy with additional stress factors such as chilling temperatures or pollution.
So, the correct answer is option (b) photolysis.

Note: Carotenoids have two important roles in plant and algae:
-They absorb light energy for use in photosynthesis
-They protect chlorophyll from photooxidative damage.