Plant

From ArticleWorld

Plant

Plants are a major group of living things. Aristotle described plants as living things that do not move and do not have sensory organs. There are about 300,000 species of plants. Plants have developed from prehistoric times, as witnessed in fossils. A large variety of plants continue to develop to this day. Linnaeus also had a system for organizing living things. In this system, plants were in the Kingdom Vegetabilia, which later turned into the Kingdom Plantae. Plants come in many forms, such as trees, flowers, tropical plants, herbs, ferns, and some algae and fungi. The large variety of plants makes them interesting to study.

Importance

The photosynthesis and carbon fixation conducted by land plants and algae are the ultimate source of energy and organic material in nearly all habitats. These processes also radically changed the composition of the earth's atmosphere, which, as a result, contains a large proportion of oxygen. Animals and most other organisms are aerobic, relying on oxygen to use energy. Therefore, plant life is essential to the ecology of the Earth.

Much of human nutrition depends on cereals. Other plants that are eaten include fruits, vegetables, herbs and spices. These plants are an important source of building materials. Some plants, known as trees and shrubs, produce woody stems. Animals also depend on plant life for food and shelter. A number of plants are used decoratively. These plants are known as flowers.

Growth

It is a common misconception that most of the solid material in a plant is taken from the soil, when in fact, almost all of it is actually taken form the air. Through a process known as photosynthesis, plants use the energy in sunlight to convert carbon dioxide from the air in to simple sugars. These sugars are then used as building blocks and form the main structural component of the plant. Plants relay on soil primarily for water, but also obtain nitrogen, phosphorus, and other crucial nutrients.

Types

One simple type of plant, like algae, has a very short life span. Other plants may be organized according to their seasonal growth patterns:

Annual: lives and reproduce within one growing season. Biennial: lives for two growing season and usually reproduce the second year. Perennial: lives for many growing seasons and continues to reproduce once the plant matures.

Annual plants are sunflowers, zinnias, cosmos, and cornflowers. Perennial plants include both evergreens and deciduous plants. Evergreens are plants that keep their leaves throughout the year. Deciduous plants loose their leaves at a specific time each year depending on climate.