Nearly every plant you see outdoors had its beginnings as a seed. A plant begins to grow when a seed germinates, usually when water causes the embryo inside the seed to swell and break out of the tough outer seed coat.
During the earliest stages of plant growth, the first root, called the taproot, stretches downward into the soil in search of water and to establish a firm structural foundation for the plant. The root grows both by adding cells and by elongating cells that already exist. Before long, the root forms branches, which improve the plant's support system and its ability to absorb water from the soil.
Not long after the taproot has become established in the soil, the shoot, or stem, of the seedling begins to stretch upward in search of light. The time-lapse video of this reveals the seedlings' need for light: They bend first one way and then the next in what becomes a repetitive waving motion as they follow the sun's movement throughout the day.
So far, all of the energy that the plant requires for growth comes from food stored in the part of the seed called the endosperm. As the stem stretches skyward it carries with it what is left of the food stores in the endosperm. Before long, however, this food will be depleted and the plant will need to create its own food. To do this, the plant must first grow leaves.
Leaves contain a chemical called chlorophyll -- a pigment that gives green leaves their color and allows plants to collect the sun's energy and use it to convert carbon dioxide and water into sugars and other carbohydrates. This chemical conversion, called photosynthesis, is the process the plant will use to produce energy for the rest of its life.
Most plants can survive with a combination of these three parts: roots, stems, and leaves. To reproduce (produce their own seeds and, eventually, their own plant offspring), however, most plants must first produce flowers. Flowers produce the pollen and eggs that, when combined with another flower's pollen or eggs, become seeds that can germinate and grow into a new plant. Many flowers, including the sunflower seen in the video, lure insects and birds to them with rewards of pollen and nectar. In exchange, these animals unwittingly carry pollen to other flowers and fertilize the eggs they contain.