Question #ce8f3

1 Answer
Apr 9, 2014

Plants absorb energy only from the red and blue ends of the visible electromagnetic spectrum. They reflect the unused green light to our eyes.


Plants use visible light (400 nm to 700 nm) for growth and photosynthesis. The wavelength of red light is about 650 nm. Green light has a wavelength of about 510 nm, and the wavelength of blue light is about 475 nm.

Photosynthesis depends on on the absorption of light by pigments in the leaves of plants. The most important of these pigments is chlorophyll-a.

Chlorophyll has its greatest absorption at 430 nm and 660 nm.

Other pigments such as chlorophyll b and β-carotene also contribute. They absorb at different wavelengths and pass their energy to chlorophyll a.

The combination of all the pigments gives the absorption spectrum shown above, but most of the energy still comes from the red and blue ends of the spectrum .

Leaves appear green because chlorophyll molecules in leaf cells absorb red and blue wavelengths. The unabsorbed green and yellow wavelengths are the colours that our eyes see.