The giant kelp is a multicellular protist, even though most protists exist as unicellular organisms. Although the kelp is a multicellular protist, it’s still not considered a plant. Kelps lack the complexity of plant cell and tissue structures that carry water and nutrients. In fact, they don’t even have roots, instead, they are attached to rocky seafloors by a structure called a holdfast. This allows them to absorb nutrients through all parts of their tissues, unlike plants that primarily use their roots. The constant flow of water provides a continuous supply of nutrients that can be absorbed by the kelps.
http://www231.pair.com/fzwester/courses/bis10v/week7/12algae.html
The outer cell wall structure of brown algae consists of cellulose that is reinforced by alginic acid. This structural part is embedded in with soluble alginates (calcium alginate) and polysaccharide fucoidan to make the matrix. Alginic acid is a gelatinous carbohydrate found in the salt form known as alginate when it associates with metals. A fun fact about alginic acid is when it is combined with aluminum hydroxide and magnesium carbonate, it can be used as a drug to treat symptoms of gastrointestinal issues, such as stomach ulcers and heartburn.
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-46702004000200009
The plasma membrane exists beneath all of these components and encircles the cytoplasm. The plasma membrane also contains plasmodesmata, which are extensions of the cytoplasm that pass through the cell walls of one cell to neighboring cells and allows for transport and communication.
Brown Algae Cell Wall Structure
The basic organelles within the cytoplasm consist of the nucleus, nucleolus, nuclear and cytoplasmic endoplasmic reticulum, mitochondria, Golgi bodies, and plastids. Physodes pictured below are membrane-bound vesicles that contain phenolics, which,”… play a multiplicity of roles within the life cycle of the algae, from the early developmental stages, (such as eggs, zygotes) to the adult plants in areas such as cell wall formation, adhesion, polyspermy prevention, defense, and UV protection.” Chloroplasts are a specific type of plastids that contain chlorophyll and conduct photosynthesis. The pyrenoids are microcompartments inside of chloroplasts that aid the enzyme Rubisco in photosynthetic CO2 fixation during the Calvin cycle. Another structure inside the chloroplast is the thylakoids which exist in stacks of three, a unique feature in brown algae, and is the site for the light reaction of photosynthesis. Laminarin vesicles contain laminarin, which is the polysaccharide form of glucose that brown algae stores its sugars in.
https://slideplayer.com/slide/9987675/
