A seed has almost everything it needs to become a plant neatly tucked inside of it, save the water that is the trigger for germination. Seeds have three parts: an embryo, the nutritive tissue that surrounds the embryo, and the protective seed coat. 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.
Once the seed coat has sensed that conditions are right for growth, it will begin to let water into the seed. It absorbs water, swelling until the seed bursts open. As the seed is absorbing water, the embryo awakens and begins to grow, feeding on the nutrients in the tissue surrounding it. These nutrients include proteins and carbohydrates.
Once the seed opens, a radicle emerges. The radicle is the precursor to the root of the plant. It grows downward, searching for more water and nutrients in the soil. Shortly after the radicle begins to grow downward, a plumule, or shoot, emerges from the seed. Unlike the radicle, the plumule grows upward. 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.