Why do plants need roots rather than digestive systems?
None of the above. Plants extract water from the soil with their roots, take carbon dioxide from the air, bring it to the chlorophyll (the green pigment of plants) which takes the energy of sunlight and builds nearly all the food and structures the plant needs. The roots also bring up other chemicals that the plants need, but they don’t get energy from them. Plants need a small amount of nitrogen and phosphorus, just as we need a small amount of vitamins. Most plants must get these from the soil. Even though air has nitrogen in it, it is tightly bound in the form of molecules and very difficult to get at. Some plants, like pea plants, keep tame bacteria in nodules in their roots to do this nitrogen fixing.
