What Enables Plants to Convert Light Energy to Chemical Energy?


Plants use energy from the sun in the form of light plus water and carbon dioxide from the air to make glucose, a carbohydrate that plants use for energy. This process is called photosynthesis. The simple formula for photosynthesis is carbon dioxide from the air plus energy from the sun plus water equals carbohydrates plus oxygen. Plants use the carbohydrates for food; animals breathe the oxygen.


Light comes in waves of elementary particles called photons. Different wavelengths of photons, the distance between the peaks and troughs of the waves, cause different colors of lights. Special structures in leaves called chloroplasts contain chlorophyll. Chlorophyll absorbs waves of blue and red light and reflects waves of green light, which is why leaves look green. Sunlight contain lots of blue light in the spring and early summer when plants are growing and more red light in the late summer when fruits are ripening.


A complex ring of carbon, nitrogen and hydrogen atoms surrounds a molecule of manganese at the center of chlorophyll. This is called the porphyrin ring. The leaves ordinarily contain the chlorophyll of a plant. Most photosynthesis takes place in the leaves, although it takes place in the stems of some plants and in the bark of some trees.

Thylakoid Membrane

The tops and bottoms of leaves are called the mesophyll. The mesophyll cells contain what is called the thylakoid membrane. Chlorophyll, beta-carotene and several other pigments in the thylakoid membrane each absorb a different color of light, passing its energy to the central chlorophyll molecule.


When a photon of light strikes a molecule of chlorophyll, it moves a chlorophyll molecule's electron into a higher orbit, circling another molecule. A chain-reaction of molecules receiving electronics and spinning them off stores light energy in the form of adenosine triphosphate, or ATP. This molecular reaction is at the heart of photosynthesis, the process of converting light into chemical energy.


ATP is a form of energy currency in all living cells, both plant and animals. In photosynthesis, ATP triggers series of reactions known as the Calvin Cycle, in which enzymes take carbon dioxide from the air and hydrogen from water to make glucose. Without light, plants would be unable to produce ATP.

Leaf Structure

For leaves to conduct photosynthesis, they must receive water from the plant and gases from the air. The vascular bundles, or veins, of leaves carry water that started at the roots and transport nutrients back to the plant. The stomata are pores on the surface of leaves that take in carbon dioxide and release oxygen in a process called transpiration.

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About this Author

Richard Hoyt, the author of 26 mysteries, thrillers and other novels, is a former reporter for Honolulu dailies and writer for "Newsweek" magazine. He taught nonfiction writing and journalism at the university level for 10 years. He holds a Ph.D. in American studies.