Diatoms are microscopic single-celled algae of the class Bacilliariophyta, and are one of the most common types of algae. Most diatoms are single-celled, but others can form colonies of algae. Diatoms secrete silica, the same material that sand is made of, that helps them build strong cell walls. They are found in the upper layers of the world’s oceans, freshwater bodies, soil, rocks and moist surfaces. Diatoms, like all algae, are photosynthetic; obtaining their energy from the Sun. they reproduce asexually by division. Due to their abundance, diatoms form an important part of the oceanic food chain, either directly or indirectly.
Size and shapes
Diatoms belong to a group of phylum known as the bacillariophytes. Diatoms’ cell shapes are either round (centric), radially symmetrical or elongated (pennate), bilaterally symmetrical. Tens of thousands of different diatom species have been identified, with many more species being continuously discovered. Diatoms lack flagella; however, flagella are only present in male gametes. They show a distinctive yellowish-brown color due to the pigment fucoxanthin present in the chromoplasts. Other pigments, such as chlorophyll a, c and B-carotene may also be present. Diatoms are encased within a cell wall (frustule) made of silica that consists of two halves; the larger one is the epitheca and the lower one the hypotheca, with one half overlapping the other half. At the point where the halves overlap, circular pieces form the girdle.
Diatoms vary in size ranging from 10-20μm across. Their siliceous walls may be patterned with a variety of pores, minute spines, grooves and holes. The frustule shape and varied patterns may be used to classify some species. Even though, the cell shapes are usually circular, some cells may have a square, triangular or an elliptical shape. Diatoms are unicellular, but they also can form colonies of various kinds. Diatoms are principally photosynthetic organisms; however, some are heterotrophs, while others can thrive in the absence of light, given there is a source of carbon in the environment. Diatoms are found in significant quantities in plankton and are of great importance in aquatic food chains, such as those in rivers, lakes and the oceans.
Reproduction
Diatoms reproduce asexually by binary fission. Each valve produces a new smaller valve. This process is repeated until the frustule reaches a very small size, during which the nucleus undergoes meiosis and produces gametes which are released, thus, a new cell is produced and the cycle gets repeated. The ability of diatoms of repeatedly manufacture valves may be of great utility in nanotechnology. It is thought that their ability to produce valves of different shapes and sizes could be used to produce Nano scale devices for solar cells and optical systems, moreover, diatom valves could be used as vehicles to deliver drugs.
Habitat
Diatoms are found in almost every aquatic and semi-aquatic ecosystem in the world, such as oceans, rivers, lakes, moist soils and damp surfaces. They are evenly distributed in the marine environment vertically and horizontally. Freshwater and marine diatoms usually go through prosperous and non prosperous lifecycles. Usually favorable conditions, such as those in the spring season, when there is plenty of light and nutrients, allow them to attain a high growth rate among phytoplankton communities. While, during unfavorable conditions, such as those when there is a depletion of nutrients, diatoms must sink to deeper waters, and only return to the surface when a mixing of waters replenishes nutrients in the upper ocean layers.
Evolution
Diatoms have inhabited the freshwater and salt bodies of the world for around 15,000,000 years. The decomposition and decay of diatoms produces sediments, which are used as index fossils to derive the age of ancient sediment deposits. Their siliceous remains form the substance of diatomaceous earth. Diatomaceous earth is used as a pesticide and for manufacture. Diatoms in marine and freshwater sediments are used to derive the conditions that were present in the past history of the Earth. The geological record present in marine deposits allow scientists to extract marine and mud cores. Phycology is a field of research that studies diatoms and their presence in the present in relation to the past.
Diatoms are microscopic unicellular plants that occur in almost every habitat that contains water, including not only the oceans, but rivers, lakes, ponds, streams and even soil and rocks. The great production of lipids in certain diatom species has generated an increased interest in diatoms as a source of biofuels. According to westerndiatoms.colorado.edu, diatoms are used extensively in the assessment of the environment due to their tolerance to environmental variables, and their silica cell walls help scientists derive the type of habitat to which particular species have adapted.
