Q: How Do Plants Make - Peabody Elementary Science...

March 2003 17

Experts answer teachers’ questions about everyday science.

A:

Q: How Do Plants MakeTheir Own Food?

Plants make their own foodthrough a process called

photosynthesis, a term that comesfrom the Greek language, meaning“arranging with light.” In the sim-plest terms, plants make their ownfood by absorbing the light energyof the sun and storing it in thechemical bonds of a sugar mol-ecule. They are the only organismscapable of such a feat.

Plants make this sugar for theirown use, but we and other animalstake advantage of their efforts byharvesting the plants for our ownfood. The sun is our planet’s ulti-mate source of energy. Humans andother animals depend on plants totransform the sun’s light energy intofood energy.

Not only do we use the energy-rich molecules of plants directlywhen we eat an orange or potato,but also indirectly when we con-sume animals that have consumedplants. It is often said that plantstruly carry out the most importantprocess on the planet. Now let’stake a closer look at the process ofphotosynthesis itself.

Carbon Dioxide+ Water = SugarThe basic product of photosynthe-sis is a sugar called glucose. Essen-tially, a complex molecule calledchlorophyll first absorbs the sun’slight energy. Chlorophyll is the pig-ment that gives plants their greencolor. It is packaged in chloroplastswithin the plant’s cells. Chlorophyll

then uses the light energy tobind several carbon diox-ide and water molecules,yielding glucose.

Thus the carbon, oxygen,and hydrogen of thesimple, low-energy mol-ecules of carbon dioxide andwater are put together into amore complex and energy-rich glucose molecule.

The plant itself can thenuse the glucose for its own im-mediate energy needs or canconvert it to the storage productof starch or other sugars such asfructose (the common sugar infruits) and sucrose (our tablesugar). We then harvest the plantand use its stored starch—in theform of potatoes, beans, or wheat—or sugars found in oranges, grapesand other fruits.

Insectivorous PlantsSome plants supplement their dietsby trapping and “digesting” insects.Various plants such as Venus’sflytraps, pitcher plants, and sun-dews incorporate different strategiesto trap insects and “digest” them byproducing powerful enzymes thatbreak down the insect bodies. But,rather than being food that providesenergy, the plants use the nutrientproducts of the digested bodies—particularly nitrogen—as fertilizer.Many insectivorous plants arefound in nutrient-poor soils andhave most probably evolved theirinsect trapping strategies as an adap-

tation to their nutrient-poor soils.

Not only do plantsprovide themselves

and us with food en-ergy, but one ofthe by-productsof photosynthesis

is the produc-tion and releaseof oxygen. Infact, plants pro-

duce practically allthe oxygen in ouratmosphere!

Robert George is a bota-nist at the Botanical Re-

search Institute of Texas inFort Worth, Texas. He

sometimes helps out withschool programs by dressing as a1800s botanist and talking about thehistory of plant collecting.

Robert George, botanist.

Keyword: photosynthesis

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