Wherever there is sunlight, air, and soil, plants can be found. On the northernmost coast of Greenland the Arctic poppy peeps out from beneath the ice. Mosses and grasses grow in Antarctica. Flowers of vivid color force their way up through the snow on mountainsides. Many shrubs and cacti thrive in deserts that go without rain for years at a time, and rivers, lakes, and swamps are filled with water plants.
The scientists who study plants--botanists--have named and described nearly 500,000 different kinds of plants. They estimate that another 500,000 undiscovered species exist in less explored ecosystems such as tropical forests. In addition, about 2,000 new kinds of plants are discovered or developed every year. Botanists have classified more than 350,000 organisms in the plant kingdom. One thing all plants have in common, however, and what separates and distinguishes them from other living things, is their ability to make their own food.
The cells of plants contain chlorophyll. Plants use chlorophyll to trap energy from the sun. They use this energy to combine carbon dioxide from the air and water from the soil to make food. This food making process is photosynthesis. Without photosynthesis, the replenishment of the Earth's fundamental food supply would halt, and the planet would become devoid of oxygen. During photosynthesis energy is used to convert carbon dioxide, water, and minerals from the environment into organic compounds and gaseous oxygen--the food we eat and the air we breathe. The process is exclusive property of the varied members of the plant kingdom.
Human beings are completely dependent upon plants. Directly or indirectly, plants provide food, clothing, fuel, shelter, and many other necessities of life. Mankind's dependence on crops such as wheat and corn is obvious, but without grass and grain the livestock that provide people with food and other animal products could not survive either.
The food that plants store for their own growth is also the food that humans and other organisms need in order to live. In North America the chief food plants are cereal grains. Major cereal crops include corn, wheat, oats, rice, barley, rye, and buckwheat. Legumes are the second greatest source of food from plants. Legumes such as peas, beans, soybeans, and peanuts are high in protein and oil. Sago, taro, and cassava are major starchy foods in certain tropical parts of the world. Seaweeds are an important part of the diet in some cultures, especially in Asia. Seasonings are derived from plant materials. People have used herbs and spices for centuries to flavor and preserve food.
Most beverages come from plants. Coffee, tea, and cocoa are prepared by steeping plants in hot water. Other drinks are "ready-made" by nature: orange, lemon, and grape juice; coconut milk; apple cider; and apricot nectar are examples. Some beverages come from processed plants, as do the cola drinks made from the kola nut of tropical America.
We rely on plants for more than just food. Virtually our whole way-of-life is dependent on plants. Many of us live in homes made from the wood of trees. Clothing, particularly cotton, is made from plants. Cosmetics, medicines, paper, pencils, furniture and--even the air we breathe--originate from plants. Have students brainstorm their own list of plant uses. The list can be extensive!
Students will understand there are so many plants, they must be classified. Plants are classified by their reproductive capability. Plants have their own Kingdom. Within this kingdom are plant divisions. For example, one Division is Anthophyta which includes flowering plants. Plants are organized into four Classes: Mosses, Ferns, Angiosperm, Gymnosperm. Mosses are primitive plants without a vascular system. Ferns are simple plants with a vascular system which are tree-like and found in shaded, moist habitats. Gymnosperms are seed plants, usually trees, whose seeds are not enclosed. Cones are an example of unprotected seeds. Angiosperms are plants that produce seeds that are enclosed, usually in fleshy fruit. Fruits, vegetables and flowers are usually angiosperms. Angiosperms are divided into two groups: monocot and dicot. Within each class is a Family, a group of plants with similar characteristics. For example, canes are similar within the Evergreen family. Within the Family, there is further division, called Genus. Within the Evergreen family, there are Spruce, Redwood and Cedar, among others. The most specific classification is called the Species. A species is defined by its ability to reproduce. A California Redwood, for example, is a specific species that will make only more California Redwoods. However, there are other species of Redwoods.