| 词条 | Frustule |
| 释义 |
A frustule is the hard and porous cell wall or external layer of diatoms. The frustule is composed almost purely of silica, made from silicic acid, and is coated with a layer of organic substance, which was referred to in the early literature on diatoms as pectin, a fiber most commonly found in cell walls of plants.[1][2] This layer is actually composed of several types of polysaccharides.[3] The frustule's structure is usually composed of two overlapping sections known as thecae (or less formally as valves). The join between the two thecae is supported by bands of silica (girdle bands) that hold them together. This overlapping allows for some internal expansion room and is essential during the reproduction process. The frustule also contains many pores and slits that provide the diatom access to the external environment for processes such as waste removal and mucilage secretion. ThecaeA frustule is usually composed of two identically shaped but slightly differently sized thecae. The theca which is a bit smaller has an edge which fits slightly inside the corresponding edge of the larger theca. This overlapping region is reinforced with silica girdle bands, and constitutes a natural "expansion joint." The larger theca is usually thought of as "upper," and is thus termed the epitheca. The smaller theca is usually thought of as "lower," and is thus called the hypotheca.[4] As the diatom divides, each daughter retains one theca of the original frustule and produces one new theca. This means that one daughter cell is the same size as the parent (epitheca and new hypotheca) while in the other daughter the old hypotheca becomes the epitheca which together with a new and slightly smaller hypotheca comprises a smaller cell. DiatomsDiatoms have varied life strategies including floating in the water column (phytoplankton), colonising submerged surfaces and living within the surface of deposited sediments. Some cells are essentially cylindrical (centric) while others have an elongated "boat-like" shape. Since they are algae belonging to the division Bacillariophyta they require light for photosynthesis. Perhaps the most studied group of diatoms belong to the phytoplankton. Phytoplanktonic diatoms rely on ocean currents and wind to keep them in the upper oceanic levels as their cell wall is denser than water around them. They would naturally sink otherwise. Diatom skeletons and their usesWhen diatoms die and their organic material decomposes, the frustules sink to the bottom of the aquatic environment. This remnant material is diatomite or "Diatomaceous earth", and is used commercially as filters, mineral fillers, mechanical insecticide, in insulation material, anti-caking agents, as a fine abrasive, and other uses.[5] There is also research underway regarding the use of diatom frustules and their properties for the field of optics, along with other cells, such as those in butterfly scales.[2] Frustule formation{{Expand section|date=February 2008}}As the diatom prepares to separate it undergoes several processes in order to start the production of either a new hypotheca or new epitheca. Once each cell is completely separate they then have similar protection and the ability to continue frustule production.[6] A brief and extremely simplified version can be explained as:[6]
References1. ^{{cite web|url= http://www.ucmp.berkeley.edu/chromista/diatoms/diatommm.html|title= Diatoms: More on Morphology}} 2. ^1 Access to articles : Nature Nanotechnology 3. ^Progress in Phycological Research: v. 7 (1991) by F.E. Round (Volume editor), David J. Chapman (Volume editor) 4. ^Diatoms: More on Morphology 5. ^Diatom Frustule 2 6. ^1 Exploring Bioinorganic Pattern Formation in Diatoms. A Story of Polarized Trafficking - Zurzolo and Bowler 127 (4): 1339 - PLANT PHYSIOLOGY External links
Regarding the Super formula
2 : Algal anatomy|Diatom biology |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。