Question

Leaves are green due to the presence of a green coloured pigment, called chlorophyll. The main function of the chlorophyll is
(a) To absorb carbon dioxide from the atmosphere.
(b) To absorb minerals and water from the soil.
(c) To give greenish colour to the leaves.
(d) To perform photosynthesis in the presence of sunlight.

Answer 1

Chlorophyll is one of many related green pigments present in cyanobacterium mesosomes and in algae and plant chloroplasts. Its name derives from the word khloros, phyllon, in Greek. In photosynthesis, chlorophyll is important, enabling plants to absorb energy from light.

Complete answer:
In the blue part of the electromagnetic spectrum and the red portion, chlorophylls absorb light most strongly. In comparison, it is a weak absorber of the green and near-green parts of the spectrum that it represents, creating the green colour of tissues containing chlorophyll. In the photosystems of green plants, two forms of chlorophyll exist chlorophyll a and b.
For photosynthesis, chlorophyll is important, which helps plants to absorb light energy. Chlorophyll molecules are organised in and around photosystems that are embedded in chloroplasts' thylakoid membranes. Chlorophyll performs three roles in these complexes. Light absorption is the feature of the vast majority of chlorophyll (up to several hundred molecules per photosystem). Having done so, these same centres perform their second function: the transfer of the light energy to a particular chlorophyll pair in the photosystems' reaction centre by resonance energy transfer. This pair affects chlorophylls' final feature, separation of charge, leading to biosynthesis. Photosystem II and photosystem I, which have their own different reaction centres, named $P680$ and $P700$ respectively, are the two currently approved photosystem modules. These centres are named after the limit of their red-peak absorption wavelength (in nanometers). In each photosystem, the identity, function and spectral properties of the chlorophyll forms are distinct and determined by each other and the protein structure that surrounds them. These chlorophyll pigments can be divided into chlorophyll a and chlorophyll b after they have been removed from the protein in a solvent (such as acetone or methanol).

Additional information: Without the assistance of other chlorophyll pigments, reaction centre chlorophyll-protein complexes are able to directly absorb light and carry out charge separation events, however, the likelihood of that occurring under a given light intensity is minimal. Thus, in the photosystem and antenna pigment proteins, the other chlorophylls all cooperatively absorb and funnel light energy to the reaction core. Apart from chlorophyll a, there are other pigments that occur in these pigment-protein antenna complexes, called accessory pigments.
So, the correct answer is ‘(d) To perform photosynthesis in the presence of sunlight’.

Note: The electron flow provided by the chlorophyll pigments of the reaction centre is used to pump $H^+$ ions through the thylakoid membrane, creating the chemiosmotic potential used primarily to produce ATP (stored chemical energy) or to reduce $NADP^+$ to $NADPH$. $NADPH$ is a universal agent used both in sugars and in other biosynthetic reactions to reduce Carbon dioxide.