Virtually all other living creatures depend on plants to survive. Through photosynthesis, plants convert energy from sunlight into food stored as carbohydrates. Because animals cannot get energy directly from the sun, they must eat plants (or other animals that have had a vegetarian meal) to survive. Plants also provide the oxygen humans and animals breathe, because plants use carbon dioxide for photosynthesis and release oxygen into the atmosphere.
Plants are found on land, in oceans, and in fresh water. They have been on Earth for millions of years. Plants were on Earth before animals and currently number about 260,000 species. Three features distinguish plants from animals:
Plants have chlorophyll, a green pigment necessary for photosynthesis;
Their cell walls are made sturdy by a material called cellulose; and
They are fixed in one place (they don’t move).
Plant Classification
In order to study the billions of different organisms living on earth, biologists have sorted and classified them based on their similarities and differences. This system of classification is also called a taxonomy and usually features both English and Latin names for the different divisions.
All plants are included in one so-called kingdom (Kingdom Plantae), which is then broken down into smaller and smaller divisions based on several characteristics, including:
Whether they can circulate fluids (like rainwater) through their bodies or need to absorb them from the moisture that surrounds them;
How they reproduce (e.g., by spores or different kinds of seeds); and
Their size or stature.
The majority of the 260,000 plant species are flowering herbs. To describe all plant species, the following divisions (or phyla) are most commonly used to sort them. The first grouping is made up of plants that are non-vascular; they cannot circulate rainwater through their stems and leaves but must absorb it from the environment that surrounds them. The remaining plant species are all vascular (they have a system for circulating fluids). This larger group is then split into two groups: one that reproduces from spores rather than seeds, and the other that reproduces from seeds.
