Light Energy and Photosynthetic Pigments

Light Reactions:

– require chlorophyll and take place in thykaloid membranes

– absorb light energy and transfer it to ADP and NADP+

– energy is transferred to carbohydrate molecules in the Calvin cycle

Carbon Fixation:

– incorporate molecules of CO_2(g) into organic molecules, such as glucose

– require energy from ATP and NADPH

– takes place in the stoma by means of the Calvin cycle

Light (Electromagnetic (EM) radiation:

– is a form of energy that travels as photons

– photons are wave packets characterized by their wavelength and energy

– photons with short wavelengths have high energy and photons with long wavelengths have low energy

Electromagnetic Spectrum:

– Sun light is a mixture of photons of different energies

– photons of different energies can be separated when passed through a transparent prism in a spectroscope forming the electromagnetic spectrum

– humans can see light between 380nm (violet)-750nm(red), but the rest is invisible

– thylakoid membranes have clusters of photosynthetic pigments, called photosystems, that absorb photons

Chlorophyll

Chlorophyll a and b:

– absorb photons in the blue-violet and red regions of the spectrum

– reflect photons in the green region of the spectrum

– chlorophyll a is the only pigment that can transfer light energy to the carbon fixation reactions

– cholorphyl b acts as an accessory pigment, absorbing photons that chlorophyll a absorbs poorly or not at all

Accessory Pigments

– transfer their energy to chlorophyll a

– chlorophyll a and b combined with accessory pigments, absorb light within the entire visible spectrum

Carotenoids:

– able to absorb light energy in the range from 400nm to 500nm

Plant carotenoids:

-some carotenoids absorb light which would otherwise damage chlorophyll, and then they lose light as heat

Human carotenoids

– similar compounds to plant cartenoids are thought to protect the eye from excessive photon damage

– b-carotene is converted to rhodopsin, a photopigment in the eye that helps vertebrates see in low-light conditions

– carrots are rich in b-carotene help maintain good vision

Leaf Colour:

– leaves appear green because of the high concentration of chlorophyll in the chloroplasts of leaf cells

– leaves appear different colours in autumn as plants stop producing chlorophyll and disassemble those already in the leaves; causes the yellow (xanthophylls), red (carotenoids) and brown pigments to become visible

William Anderson (Schoolworkhelper Editorial Team)

William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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