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Diatom

From CreationWiki, the encyclopedia of creation science

Diatoms

Scientific Classification
Domain: Eukaryota Kingdom: Protista Phylum: Heterokontophyta Class: Bacillariophyceae
Orders
Centrales Pennales

Diatoms are a unicellular organism that is well known as phytoplankton. They are distributed all over the watery areas. They influence the world in lots of ways. They are responsible for 23% of the primary reproductive of the world, which means that they photosynthesize about one- quarter of the world. As a result, they play an important role for the food web. [1] Although diatoms can reproduce either sexually or asexually, they usually reproduce asexually, but as they reproduce asexually, they get smaller. Diatoms are divided into two orders: centric diatoms (Centrales) that is round and pennate diatoms (Pennales) that is thin ellipse. Diatoms are one of the most beautiful organisms to look under the scope; especially the pattern of areolae, holes that are needed to obtain nutrient and gases, is amazing. [2]

1 Classification
2 Anatomy
3 Reproduction
4 Ecology
5 Gallery
6 Related References
7 See Also

Classification

The opinion over classification of heterokonts is still debated. They can be either considered as a phylum, or kingdom, or some where between. Consequently, diatoms may be arranged anywhere from class (Bacillariophyceae) to a phylum (Bacillariophyta). Diatoms are also sometimes called Class Diatomophyceae.

There has been a recent revision for the classification of the diatom. According to the recent classification, diatoms are divided into three classes: centric diatoms (Coscinodiscophyceae), pennate diatoms without a raphe (Fragilariophyceae), and pennate diatoms with a raphe (Bacillariophyceae). The classification of diatom is likely to be revised in the future. [3]

Anatomy

Appealing patterns of areolae

Diatoms are encased in two distinct valves, which are made of silica. The larger, older valve that cover the other one is called the epivalve, and the smaller, younger valve that is covered by epivalve is called hypovalve. Two valves are hooked up by a girdle region. Diatoms often carry one or more spines that are known as setae. The setae are a quite unique part of diatoms since they may be many times longer than the diameter of the cell. These spines help diatoms to move vertically.

Diatom valves are equipped with areolae, numerous 0.1 ~ 0.6 micron hexagonal holes. Areolae is necessary for the diatom to obtain nutrient and dissolved gasses such as CO2 from the seawater, because no molecules or ions can go through the solid silica sheet that is covering the diatom. Areolae are arranged in alluring, regular patterns. [4]

The appearance of the diatom, especially the patterns of areolae, has appealed to microscopist for more than twenty years. Diatoms are one of the organisms that make people willing to look under the scope. [5]

Reproduction

Diatoms can reproduce in two different ways.

First of all, diatoms can reproduce asexually. Reproducing asexually is the basic method how diatoms reproduce. Diatoms have a distinctive mode called “shrinking division,” which is used in asexual reproduction. After cell division, two valves that encase the diatom separate. Each valves become the epivalve of a daughter cell, and new hypovalve is secreted to encase the daughter cell. As a result of the cell division, one daughter cell becomes the same size of mother’s, and another daughter cell becomes a little bit smaller. Consequently, the average size of diatom gets smaller as asexual reproduction is processed.

When diatoms get so small as a result of asexual reproduction, they switch to sexual reproduction. Meiotic cell division, which occurs in a parent cell, makes eggs or sperm. Auxphore that is formed when sperms find eggs split two valves of diatom and start to grow. When the process of growing is almost complete, test secretion occurs. If they think they’ve grown enough, they change to asexual reproduction.[6]

Ecology

Diatoms are one of the organisms that influence the world very much. Diatoms are responsible for 23% of the primary reproductive of the world. This means that almost one quarter of photosynthesis is processed in a diatom. As we can see from the proportion of the diatom’s photosynthesis, we can predict that there are many diatoms in the world. Since they are primary producers, they play a core role in marine food webs.[7]

Diatoms live in freshwater streams and lakes as well as light zone of every zone. Diatom lives in almost any watery point relying on its lifestyle known as boom and bust. When the condition in the upper layer such as nutrient or sunlight is favorable, they boom by dominating phytoplankton communities. When condition in the upper layer is not favorable, especially nutrient, they bust either by losing a buoyancy control, or by producing heavy resting spores. Because of their ‘boom and bust’ lifestyle, diatoms play a considerable role in export of carbon from oceanic surface waters. [8]

Gallery

A model of diatom

Scanning Electron Micrographs of Diatoms. (A) Biddulphia reticulata. Order: Centrales (B) Diploneis sp. Order: Pennales (C) Eupodiscus radiatus. Order: Centrales (D) Melosira varians. Order: Centrales