Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)

All living things use chemistry, not just people and animals. A large part of the tree of life is the plant kingdom. Since plants can’t run away or fight with tooth and claw, they have developed quite sophisticated chemical methods to get what they need or defend what they have.

Many of the chemical changes you see in plants have to do with their color. The leaves change color with the seasons, flowers come in bright colors to attract pollinators, and even the green of the leaves is due to the important chemistry involved with making sugar from water, air, and sunlight.

Do we get chemicals from plants?

We use plants mostly for food. Any industrial uses for plants would compete for land that could be growing food, or for food itself. Despite that, there are many industrial chemicals that are made from plants.

An example is the alcohol that is added to gasoline. Normal economics would prevent corn from being used to power cars, since it is more valuable as food. But governments pay distillers to make alcohol from corn, so that corn prices will be higher and benefit the corporations that grow the corn.

But there are many non-food products that can be more cheaply grown than manufactured. Carnauba wax, candelilla wax, jojoba oil, gum arabic, gum tragacanth, and natural rubber are just a few.

In some cases, plants are most useful as sources of chemicals, such as in medicine and pest control. Because plants make many very complex molecules that are very hard to produce synthetically, many medicinal proteins and drugs come from plants. Roughly one-quarter of all prescription drugs are derived from plants.

Plant-derived insecticides and insect repellants are another class of molecule that is cheaper to get from plants than to try to make in a lab. These molecules also have the benefit of being easily biodegradable, so they don’t linger in the environment.

Plant-derived dyes are another class of chemicals that are cheaper to grow than to make. Carotenoids—the red, yellow, and orange molecules in autumn leaves—are widely used in industry. Indigo blue, the browns of henna, and the yellows of saffron and turmeric are other examples.