Looks like a plant but is really a protist…

Most seaweed is photosynthetic. Some are not producers but parasites of other seaweeds. Seaweeds transform solar energy into chemical energy in the form of organic matter. This organic matter is available to many other organisms.

Seaweed is a type of marine algae, it can also be referred to as a macrophyte or macroalgae. Seaweed is multicellular and eukaryotic. Seaweeds lack highly specialized structures and reproductive structures that are characteristic of terrestrial plants. Seaweeds show a wide range of growth forms and complexity of structures.

Seaweeds lack true leaves and roots. The complete body is called the thallus. It can be a filament, thin leafy sheet or giant kelp. The leaf like, flattened portion of the thallus is known as the blade, these have no veins. Gas-filled bladders, called pneumatocysts, sometimes keep the blades close to the sea surface.

Some have a distant stem-like structure that provides support, this is called the stipe. Blades originate from the stipe. A structure that looks like roots attach the thallus to the bottom. This is called the holdfast.

These help anchor the seaweed. They cannot usually cannot anchor in soft sediments and are restricted to hard bottoms. These do not penetrate through sand or mud like true roots do, so they are not involved in the absorption of water and nutrients. They also usually lack tissues specialized in the transport of water and nutrients. Water and nutrients are picked up across the surface of the thallus.