In land plants, this occurs in the leaves. In large brown seaweeds, a structure called the blade contains the special cells needed to perform this function. Other seaweeds have photosynthetic cells all over the entire plant. The blade may have a gas sac attached to it which helps keep it near the surface. It is important for the blade to r emain near the surface so that it can get the sunlight needed for photosynthesis.
Some seaweeds have pneumatocysts as large as baseballs.
If a blade is present, as in the brown seaweeds, it is attached to a flexible structure known as the stipe. The stipe is flexible and easily bends with the waves and currents. The base of the stipe broadens to form the holdfast. The holdfast can be dis c shaped or it may resemble a root, but it does not perform the same functions as a root. In land plants, roots transport nutrients from the soil to leaves.