Like all living things, green plants have their own cycle of birth, life and death. The length of the life cycle varies according to the type of green plant. Annuals go through an entire life cycle within a year. Biennials live for two years but produce flowers, fruit and seeds only during their second growing season. Perennials live for several years and reproduce every year, but often go through a period of dormancy between growing seasons. Despite their differences, though, all green plants share the same basic elements within their life cycle.
During the first stage of the life cycle, the previously dormant seed sprouts and begins to grow. The seedling plant puts down roots, grows a stem that pushes toward the sun or other light source, and begins to form leaves in order to make food through photosynthesis. During this stage, the green plant's greatest needs are warmth, air and water.
During the growth stage of the life cycle, the green plant engages in photosynthesis, or the use of carbon dioxide and sunlight to make food for itself. All the plant's energy is focused on creating food as it grows from a seedling into a mature plant. The plant is more resistant to cold, but still requires air, light and a certain amount of heat. Once growth is complete, the plant produces a flower.
The flower is the most notable feature of most green plants, and marks the beginning of the reproductive stage of the life cycle. Wind, animals or insects spread pollen from flower to flower. The pollen then fertilizes the egg cells within the flower. Once the flower is pollinated and fertilized, the flower withers and seeds begin to form.
The formation of fruit marks the maturity of the green plant. The fruit, or plant ovary, forms as the seeds mature. The main function of the fruit is to disperse the seeds, so ripe fruit signals mature seeds that are ready to scatter. Once the seeds are mature, the plant either dies---ending that particular plant's life cycle---or begins to go dormant until another growing season.
Seeds from green plants are scattered by wind, water or animals in a variety of ways. The seeds then fall to the ground and lie dormant until conditions are ripe for germination to continue the life cycle.