How Does a Seed Become a New Plant?
Inside the shell, or seed coat, of a seed are the tiny beginnings of the new plant, called the embryo. The embryo lies dormant until the seed is ready to sprout. While it is dormant, the seed coat protects the seed until the light-sensitive chemicals located in the coat signify that conditions are ripe for growing. That notification, plus a supply of water, is the trigger for germination.
The remainder of the soft inside part supplies food for the baby plant. In order to sprout, a seed must have moisture and the right temperature. When a seed is planted, it swells with moisture so that it bursts its seed coat. At this point the embryo begins to grow.
First the root begins growing downward. Then the beginning of the stem and the first leaves push upward into the air and sunlight, which the seedling needs to grow into a whole plant. Once it reaches the air above the ground and forms the first leaves (seeds leaves), the plumule becomes a cotyledon; a very young plant.
As long as the plant continues to have access to adequate water, sunlight and nutrients, it will continue to grow and develop into a mature plant, producing seeds of its own, which will ripen and disperse to continue the cycle.