Chlorophyll enables seaweeds to make their own food through photosynthesis, the process by which plants and certain other organisms use energy from sunlight to turn carbon dioxide and water into sugar. This sugar not only fuels the seaweeds' own growth and development, it also serves as food for animals that feed on seaweeds. Seaweeds also help provide sea animals with oxygen, which is released as a by-product of photosynthesis. In addition, many marine creatures find shelter in seaweed beds. There are about 7,000 species of seaweeds.
Algae lack true roots, stems, leaves, and flowers.
However, their special structure suits seaweeds to a life of pounding by the sea. Some types of seaweeds Marine algae can be found from the polar seas to the tropics. Most varieties grow near coasts, where they are attached to rocks, shells, or the floor of the sea. A rootlike part, called a holdfast, anchors larger seaweeds to solid objects and prevents them from being washed away. Unlike a true root, the holdfast is not specialized to absorb water and minerals.