Algae are simple yet large and diverse groups of autotrophic organisms that grow in water or in moist areas. They act as producers of food and oxygen. Algae may be unicellular or multicellular based on their type, and they reproduce either sexually or asexually. The algae are classified into phyla based on their type of chlorophyll, the form of food-storage, the color of the algae and the cell wall composition. All of the phyla contain the chlorophyll a, and the important features of all the seven phyla are discussed in this article.
The chlorophyta is the commonly found green algae and is composed of almost 7,000 species. These algae may be unicellular, multi cellular or colonial. They are said to have given rise to the terrestrial plants. They contain the chlorophyll a, b and the orange and the yellow pigments the carotenoids. The cell wall is mostly made of cellulose but some marine forms may also add calcium carbonate. They store the food in the form of starch and may inhabit fresh water, moist areas or marine environments. Some of the examples include the ulva, spirogyra and the chlamydomonas.
These are the commonly found brown algae and the largest of all protists. The kelps and seaweeds are also included in this group. This phyla is composed of 1,500 species. They contain the chlorophyll a, c and a brown pigment called the fucoxanthin. They store the food in the form of a carbohydrate called the laminarin. They live in the cooler marine areas and have special adaptations such as the air bladders, the stipes and specialized root-like holdfasts to anchor the thallus to the rocks and to float the leaf-like blades to get sunlight for photosynthesis. Some examples of the phaeophytes are the laminaria and the fucus.
The rhodophytes are the red algae and this phylum contains almost 4,000 species. They grow in the warm marine areas and in deeper waters. Sometimes they can be found in fresh waters also. They contain chlorophyll a and the phycobilins, which are the red pigments. They store food in the form of starch, and their cell wall is made up of cellulose and agar, which is used as a culture medium for growing microbes. Some species contain the carageenan that is used for making the gelatin capsules for medicines.
This is a large phylum with more than 11,500 species and is called the phytoplanktons that start a number of food chains. They contain chlorophyll a and c, the carotenoids and the xanthophylls. Food is stored in the form of starch and their cell wall contains cellulose. They have glass-like shells that contain SiO2 that keeps the two parts together.
They are also called the pyrrophyta and are composed of 1,100 species. They store food in the form of starch and mostly contain chlorophyll a, c and carotenoids. They are yellow to brown in color and are small and unicellular, making up plankton. They often undergo algal blooms and vastly increase in numbers and produce a red poisonous substance, causing red tides.
This is the golden algae and is composed of 850 species. They mostly live in fresh water habitats and contain chlorophyll a, c, fucoxanthins and carotenoids. They can form highly resistant cysts to survive in winter under the frozen lakes.
This phylum contains 1,000 species, and they are unicellular. These algae lack a definite cell wall but have a protein covering called the pellicle. They are also called the euglenoids. They contain chlorophyll a, b and carotenoids. They live in fresh water and some in moist soil and in the digestive tracts of some animals. They store their food in the form of a polysaccharide called paramylon.