Question

The highest rate of photosynthesis in green plants is in __________ and __________ region of the light spectrum.
(a)Yellow and orange
(b)Green and violet
(c)Red and blue
(d)Violet and blue

Answer 1

Hint: The colour of the pigment comes from the wavelength of light reflected. The pigments have their own characteristic absorption spectra, the absorption pattern of a given pigment. The green colour pigment chlorophyll is present in all photosynthetic plants.

Complete answer:
Chlorophyll, the green pigment absorbs all wavelengths of visible light except green that is 550 nm, which is reflected by the leaves and detected by our eyes. All the photosynthetic organisms have chlorophyll ‘a’ which absorbs its energy from the violet-blue and reddish orange-red wavelength, and little from the intermediate green-yellow-orange wavelength of the sunlight.

Additional Information: -Accessory pigments include chlorophyll ‘b’, also ‘c’, ‘d’ and ‘e’ in algae, xanthophylls and carotenoids.
-The pigments absorb light energy which dissipates as heat.
-The energy absorbed by sunlight may be emitted immediately as a longer wavelength, a phenomenon known as fluorescence.
-The energy absorbed by sunlight may trigger a chemical reaction by chlorophyll when it is associated with protein embedded in a membrane infolding found in photosynthetic prokaryotes.
-Emerson observed that photosynthesis decreased when a plant was shifted from short-wavelength i.e. 650nm to wavelength longer than 680 nm. This decline in the rate of photosynthesis under long wavelengths of red is described as ‘red drop.’

So, the correct answer is, ‘red and blue.’

Note: -Different wavelength of light can affect how much photosynthesis can occur because only certain colours are absorbed.
-Photosynthesis depends upon the absorption of light by pigments in the leaves of plants.
-Emerson also observed that when both short and long wavelength of red light acted on at the same time the rate of photosynthesis was higher than the sum of photosynthetic rate obtained by using short and long wavelength respectively. This effect is known as the Emerson effect.