Question

In chloroplasts, highest number of protons are found in
A. Antenna complex
B. Strom
C. Lumen of thylakoid
D. Intermembrane space

Answer 1

Hint: The chloroplasts have an important role in the process of photosynthesis which is dependent upon sunlight and it divides the water molecule into protons and electrons. These protons are stored.

Complete answer:
For the process of photosynthesis, the plant is mainly dependent upon the sunlight for the feasibility of the reaction and as an energy source.
Now during the process of photosynthesis, the protons which are in the stroma are pushed towards the lumen of the thylakoid. These protons are formed as a result of the breakdown of water molecules into H+ and OH- protons and electrons by the photooxidation mediated by the energy of the sunlight. Now these electrons are transported to the cytochrome and in exchange the protons are increased inside the thylakoid space. During this transfer of the protons, there is a force which is getting developed and it is known as the proton motive force which is required for the synthesis of ATP and thus ATP is used further as the energy source in many metabolic reactions of the plant. This transfer of the protons is regulated by constant alterations in the amount of light taken up by the plants because over accumulation of the protons inside the thylakoid will result in the increasing of the electrical potential and the chemical potential along the neighboring areas.
We do not consider stroma as the proton storage site because it is responsible for the breakdown of water molecules by the sunlight and the transfer of protons. The element responsible for capturing the sunlight is the chlorophyll pigment and it only diverts the energy of sunlight by capturing the photons from it. Intermembrane space is already filled with the fluid for the permeability.

Hence, the correct answer is option (C).

Note: Stroma should not be considered as the storehouse of the protons as it only transfers them. The antenna complex is responsible for transferring light energy to one chlorophyll molecule.