ALGAE Algae can be unicellular or multicellular. There are those that are not pathogenic but are very important to the environment, such as diatoms, brown algae, red algae, dinoflagellates, and green algae because they make oxygen to a large extent and make up a great amount of the earth’s organic matter. Algae are responsible for making agar and carrageenan, used to solidify and thicken foods. Some are only harmful because they produce toxins when they come from algal blooms, which can cause nervous system and liver damage in humans and water-dwelling animals. Algae will store starches in pyrenoids within their chloroplasts as part of their metabolism. A few will have chloroplasts that have triple or quadruple membranes, depending on their evolutionary origin. Algae can be differently pigmented, depending on what pigments are in them. Seaweed is a form of algae and are not plants, even though they are macroscopic and look like plants. Algae are divided into two supergroups: the Chromalveolata and the Archaeplastida. The dinoflagellates are Chromalveolata and make up plankton. Some are phototrophic, while others are heterotrophic or mixed in how they get their energy. Dinoflagellates whirl because of their two flagella. Some can have an outer plate called a theca made from cellulose. Some are neurotoxic to fish or humans. Red tides come from overgrowth of dinoflagellates. There are stramenopiles that are what make up golden algae, brown algae, and diatoms. These are photosynthetic. The diatoms have an outer skeleton made from crystallized silica, which goes on to make diatomaceous earth. Some diatoms will contribute to toxic algal blooms. Giant kelp organisms are considered brown algae; they have holdfasts that attach them to substrates. Green and red algae are similar to land plants but are not plants. Chlorella are small unicellular algae.
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