7. Biochemical Pathways-Photosynthesis


7.4. Other Aspects of Plant Metabolism


Photosynthetic organisms are able to manufacture organic molecules from inorganic molecules. Once they have the basic carbon skeleton, they can manufacture a variety of other complex molecules for their own needs—fats, proteins, and complex carbohydrates are some of the more common. However, plants produce a wide variety of other molecules for specific purposes. Among the molecules they produce are compounds that are toxic to animals that use plants as food. Many of these compounds have been discovered to be useful as medicines. Digitalis from the foxglove plant causes the hearts of animals that eat the plant to malfunction (figure 7.10). However, it can be used as a medicine in humans who have certain heart ailments. Molecules that paralyze animals have been used in medicine to treat specific ailments and relax muscles, so that surgery is easier to perform. Still others have been used as natural insecticides.



FIGURE 7.10. Foxglove, Cannabis, and Coffee Plants

(a) Foxglove, Digitalis purpurea, produces the compound cardenolide digitoxin, a valuable medicine in the treatment of heart disease. The drug containing this compound is known as digitalis. (b) Cannabis sativais, the source of marijuana, has been show to be effective in the treatment of pain, nausea, and vomiting, and acts as an antispasmodic and anticonvulsant. (c) The plant Coffea arabica is one source of the compound caffeine and has been shown to reduce the risk of diabetes and Parkinson’s disease.


Vitamins are another important group of organic molecules derived from plants. Vitamins are organic molecules that we cannot manufacture but must have in small amounts to maintain good health. The vitamins we get from plants are manufactured by them for their own purposes. By definition, they are not vitamins to the plant, because the plant makes them for its own use. However, because we cannot make them, we rely on plants to synthesize these important molecules for us, and we consume them when we eat foods containing them.



11. Is vitamin C a vitamin for an orange tree?