The Role of Chloroplast and Light in Photosynthesis

It is the driving energy of photosynthesis Light is visible part of solar radiations. Light behaves as waves as well as short of energy called photons. The visible light ranges from about 389 to 750nm in wavelength. The amount of energy of a photon is inversely related to the wavelength of the light. Thus, a photon of violet light has nearly twice as much energy as a photon of red light. However in photosynthesis, number of quanta (photons) is more effective than the energy of quanta.

As the sunlight comprises of wide range of wavelengths. Only the rays of suitable wavelengths are absorbed by the chlorophylls.

Absorption spectrum of chlorophylls indicates that absorption is maximum in blue and red parts of the spectrum.

On absorption of light the electrons of chlorophyll get excited. The electron carries of ETC (Electron Transport Chain) then transport them & during their transport Chemiosmosis or formation of ATP & reduction of NADP to NADPH takes place

Chlorophyll

These are different kinds of chlorophylls. The chlorophyll a, b, c and d are found in eukaryotic photosynthetic plants and algae while the other are found in photosynthetic bacteria and are known as bacterial chlorophylls.

Chlorophylls absorb mainly violet-blue and orange red wavelengths. Green and yellow wave lengths are least absorbed by chlorophylls and are transmitted or reflected, although the yellow are often masked by dark green colour, hence plants appear green.

Action Spectrum

Chlorophyll a is the must abundant and the must important photosynthetic pigment as it takes part directly in the light all photosynthetic organisms except photosynthetic bacteria.

Chlorophyll b is found along with chlorophyll a in all green plants and green algae. Chlorophylls are insoluble in water but soluble in organic solvents.

Carotenoids-accessory pigments

Carotenoids are yellow and red to orange pigments that absorb strongly the blue violet range different wavelengths than the chlorophyll absorbs. So they broaden the spectrum of light that provides energy for photosynthesis.

Thus chlorophyll b is called accessory pigment because it absorbs light and transfers the energy to chlorophyll a, which then initiates the light reaction.

Some carotenoids protect chlorophyll from intense light by absorbing and dissipating excessive light energy, rather than transmitting energy to chlorophyll.