(i) Photosynthesis cannot occur in the absence of sunlight. The sunlight originally supplies the energy for conversion of CO2 to carbohydrate.
(ii) Yes, the chlorophyll is the most prominent plant pigment, but not in all plants. Some other accessory pigments such as xanthophylls and carotenoids can also perform photosynthesis separately (in some algae).
(iii) Photosynthesis can occur under water only when the water is clear and shallow. Some alga (Rhodophyta) can synthesise food at deep water layers as they can absorb the light of blue wavelength, efficiently.

(i) Plants are also called lungs of the nature because, they perform the exact function as lungs do in mammals. They produce oxygen, which is necessary for all forms of life. So, in essence since our lungs keep us alive in the same way the trees keep our lungs alive. Thus, they are considered to be the part of our lung existence.
(ii) Chlorophyll-b and other accessory pigments are necessary as these are light absorbing compounds found in photosynthetic organisms. These pigments enable a wider range of wavelength of incoming light to be utilised for photosynthesis.
(iii) Chlorophyll-a structure is such that it gets damaged by bright/high light intensities. It is protected by carotenoid pigments.

C₄-plants are better adapted to dry tropical regions. They have the following features.
i) Can tolerate high temperatures
ii) Can perform photosynthesis in high light intensities.
iii) Have overcome the problem of photorespiration and have a greater productivity of biomass.

Group A will show more photosynthesis.
(a) Chlorophyll absorbs maximum light in the blue region of the spectrum, i.e., 400-450 nm and hence photosynthetic rate will also be high.
Group B will show negligible amount of photosynthesis or no photosynthesis.
(b) Chlorophyll does not absorb any light in the green region, i.e., 500-550 om, but reflects green.

Cyclic phosphorylation occurs when 700 nm light is available and PS-I is functional. It occurs in the stroma lamellae where enzyme NADP reductase is absent and PS-II is also absent. Hence, electrons are passed on back to PS-I and not to NADP⁺. So, the cyclic flow results in the formation of ATP, but not NADPH.