The plant kingdom is one of the five science classifications of living organisms. It is made up of some 350,000 species of shrubs, trees, land plants, ferns, mosses and algae. These plants are the primary producers of the food chain and all animal life is dependent on them. They grace the earth with their beauty and fragrance and work together to give us clean air, shelter and food.
The Kingdom Plantae can be divided into two major divisions: vascular plants and non-vascular plants. Non-vascular plants are called bryophytes and include the mosses and liverworts. Vascular plants can be grouped into those that produce seeds and those that do not. Plants that produce seeds can be divided into the gymnophytes (seeds are not contained within a fruit) and the anthophytes (seeds are enclosed within a fruit). The four types are gymnophytes are conifers, cycads, ginkgoe and gnetae. Anthophytes, which comprise about 95 percent of the plants in the kingdom, can be divided into the monocotyledons (one primary leaf) and dicotyledons (two primary leaves).
Plants are essential to the balance of nature and human and animal life. Green plants (those possessing chlorophyll) produce their own food. This process called photosynthesis combines water and carbon dioxide by the energy of light. This is a significant act as animals cannot produce their own food and depend on plants as a major source of food and metabolic energy. Plants and plant products are also vital for human sustenance. Wood, fibers, drugs, oils, coal and petroleum are just some of the many products derived from plants and plant products.
Plants come in a variety of sizes, forms and colors. They are composed of cells with a distinct cell wall, a vacuole filled with sap and different kinds of plastids. Plastids are responsible for photosynthesis and the storage of starch and other products. Plant cells can synthesize all the amino acids, coenzymes and vitamins necessary for the plant's function. Although plants are not mobile, they exhibit unlimited growth during their lifetime. Most plants are supported by a stem and roots. Some plants have leaves and flowers that develop into fruit.
Plant growth and reproduction depends on climate, soil and weather conditions. Each year in a plant's life is referred to as a "growth season" and different types of plants have different growth seasons.
Flowering plants that live and die within one year are called annuals. These plants grow, flower, set seed and die in as little as a few weeks. Biennial plants take two years to complete their life cycle. During the first year they may grow and store food. During the second year, they bloom, produce seeds and die. Some plants live for many years. They are called perennials. Perennials are divided into two groups. Herbaceous perennials lose all their visible parts each winter, only to return the following spring. Woody perennials, such as trees and shrubs, may lose their leaves during winter but the plant body (stem or trunk) remains visible. Trees that do not shed their leaves are called evergreens.
Plants can reproduce in two ways. Vegetative reproduction or propagation occurs when part of the plant, such as a bulb, develops into a new plant. This is referred to as asexual reproduction, meaning it does not involve a male and female sex cell. One method of vegetative reproduction can take the form of cuttings. Most flowering plants reproduce sexually. This sexual reproduction takes place when the male stamen and female carpels unite through pollination. Pollination allows the plant to develop seeds by which new plants can grow.