How can plants like seaweed grow underwater?

As long as they get enough sunlight to carry out photosynthesis, plants can live at various depths in oceans or other bodies of water. The stems of most underwater plants usually hold them upright so they can grow toward the light that filters down through their watery homes.

 When the countless animals that live in seas and lakes breathe, they provide water plants with the carbon dioxide they need for photosynthesis. As underwater plants release oxygen during photosynthesis, you can sometimes see it bubble to the surface (in the same way that bubbles appear when people breathe out underwater).

Seaweeds are odd underwater plants because they don’t have true roots, stems, or leaves. They are really just larger forms of single-celled algae, the simplest type of plant that exists. Many sea weeds have “fronds” that look like leaves and “stalks” that look like stems. Some even have “holdfasts” that do the work of roots, attaching them to rocks or sea beds. But these special parts don’t do different jobs, like they do in most plants. All parts of a seaweed plant absorb water, carbon dioxide, minerals, and sun light for photosynthesis.

Algae are very important plants. Water covers much of the world’s surface, which means algae cover much of the world’s surface too. All plants release oxygen as part of photosynthesis, and the large quantities of this simple plant make algae a major source of the oxygen we breathe. One of the most common types of seaweed, known as giant kelp, forms underwater forests in the oceans, providing shelter, food, and oxygen for countless sea animals. Some of these plants have fronds up to 200 feet (61 meters) long and grow up to 75 feet (23 meters) below the sea surface! (A type of red seaweed can grow even deeper up to 200 feet, or 61 meters, below the surface.) Some sea weeds are eaten by people mostly in the East and they are used to make things like fertilizers, cosmetics, and medicines.