Carapace of diatoms

Carapace of diatoms

In this microphotograph - diatom Lyrella hennedyi. We see only its shell, penetrated by a large number of pores for communication with the external environment. In the middle there is a seam (central gap), in the center - a thickening of the shell (central nodule).

Diatoms, or diatoms (class Diatomophyceae), are single-celled single or colonial microscopic organisms. Their size usually varies from 2 to 200 microns (sometimes more). They live mainly in the aquatic environment - in the oceans, seas and rivers, where they represent 3-3-333. plankton and benthos , as well as in the upper layers of the soil, on snow and in ice, in hot springs. Diatoms can also grow on animals, from crustaceans to whales (that is, be episodes), or live inside other organisms (be 3-3-3335. Endobionts 3-3-33440.) - 3-3-3337. e.g. as photosymbionts foraminifera .

The main feature of diatoms is the presence of a shell on top of cell membrane . The shell consists mainly of 3-3-345. amorphous silica similar in composition to opal , and also includes an admixture of organic substances and some metals (iron, aluminum, magnesium). The shell has two halves that are worn one on top of the other. B about the higher (upper) half is the epithecus, the smaller is the hypothec. Each half consists of a sash and a girdle. In the place where the rims overlap, a girdle forms. Depending on the angle of cell location under the microscope and in the micrograph, a view from the sash and a view from the girdle are distinguished. The main photo shows the view from the sash.

Carapace of diatoms

Volumetric diagram of the structure of the shell of a diatom algae. Cn - central nodule (shell thickening), Ec - The rim band of the epithecus, HC - girdle rim of the hypotheca, Ev - epivalva (surface of the epithecus fold), Hv - Hypovalva (surface of the hypothetical cusp), 3-3-33297. Ra [/b] - central seam, Pn - terminal nodule. Figure from an article by G. Kratosova et al., 2014.3-3r379. Synthesis of metallic nanoparticles by silica based algae - outline, prospect and applications from the book Green biosynthesis of nanoparticles: mechanisms and applications

In some diatoms, incomplete partitions of the shell can divide the cell into several communicating chambers. The shells come in different shapes, with different numbers of pores (pores can occupy up to 75% of the shell area), with or without outgrowths.

Carapace of diatoms

The variety of forms and structures of the shells of marine diatoms (3-3-33297. A 3-3-33298. - 3-3-33297. D 3-3-33298., 3-3-33297. F 3-3-33298. - 3-3-33297. I 3-3-33298.) In 3-3-3329. scanning electron microscope . e - diatomite from Australia. The length of the scale segment is - 10 microns. Photo from article D. Losic et. al., 2009.3-3r3115. Diatomaceous Lessons in Nanotechnology and Advanced Materials

In pennate diatoms (3–3–3443 also belongs to them. Lyrella hennedyi 3–3–3444. From the main photo), armor exhibits 3–3–3125. bilateral symmetry, for centric - radial .

Carapace of diatoms

Centric diatom Coscinodiscus wailesii . View from the sash (round cells) and from the girdle. The average cell diameter is 230 ?m. Darkfield microscopy . Photo from the site

Silica for the construction of the shell diatoms are obtained from the external environment, where it is presented in the form of metasilicic or orthosilicic acids (see 3-3-3157. Silicic acids 3-3-33440.). How these acids are transported into the cell is unknown; perhaps mediators are special transport proteins (see article 3-3-3159. Silicon transporter proteins: a long way to discover 3-3-33440.).

Carapace of diatoms

Marine planktonic colonial diatom 3-3-3179. Chaetoceros debilis . Cells are typically characterized by long, hollow, straight or curved spikes, which connect them in the colony, and the spikes may intersect or grow together at the base. Phase contrast microscopy 3-3-33440. , magnification 250x. [/b] Photo © Dr. Wim van Egmond [b] from the site

Most diatoms are rather slow, but some bottom and soil diatoms are able to move fast enough (at a speed of 0.2–25 ?m /s), communicating with the environment with a suture that runs along the valve itself or along the special outgrowths of the carapace - keels. The seam can be slit-like (in the form of a narrow long slit on the leaf) or canal-like (in the keel). The movement of these algae is a complex process and not fully understood, but the principle is clear: algae secrete mucus and glide along it. If you place the diatom on a microscope slide, you can observe the traces of mucus that it leaves.

Diatoms reproduce under favorable conditions (in spring and early summer), mainly 3-3-33199. vegetatively : the cell divides in half with the divergence of the halves of the carapace. The half received from the mother cell will become an epitec, and the hypothec will be completed, therefore, the cell that received the epithec will have the size of the mother, and the one received the hypothec will be smaller. Thus, over time, in a vegetatively growing population, cell sizes will decrease. This process is inhibited in different ways in different species. For example, in species of the genus 3-3-33443. Melosira [/i] smaller cells simply stop dividing over time, and only larger offspring provide population growth. And some diatoms have more elastic bands of cells, which allows them to stretch a little.

Carapace of diatoms

The structure of the shell of the diatom pinnularia (3-3-33443. 3-3-33218. Pinnularia 3-3-33440. 3-3-33444.). A - view from the side of the girdle; B - view from the side of the sash; In - lengthwise cut; D - cross section; D - vegetative propagation of . 1 - epithecus, 2 - hypothec, 3 - seam, 4 - nodule, 5 - chromatophore, 6 - pyrenoids 3-3-33440. , 7 - cytoplasm, 8 - core, 9 - vacuole, 10 - sash, 11 - belt. Drawing from the site

The grinding of the cells is compensated during sexual reproduction, however, there is no evidence of a direct connection between the onset of the sexual process and the stabilization of cell sizes in the population, since larger cells also reproduce this way. The sexual process differs in pennate and centric diatoms: in the former, it mainly occurs with flagellate 3–3–3265. gametes 3-3-33440. and in the second - with flagellate sperm. In pennate diatoms as a result of 3–3–3267. meiosis 1–2 gametes are formed in the cell, the cusps move apart, and the gamete can exit to move to another cell for fusion. In the event that two gametes are formed, only one leaves, and the second remains in the cage and waits for the mobile gamete to merge. Gametes move amoeba-like, using pseudopod ; some diatoms form a special mucous channel for the gamete transition. In centric diatoms as a result of meiosis and subsequent mitosis 3-3-33440. (sometimes numerous) from 4 to 128 spermatozoa are formed, as well as one or two eggs.

Carapace of diatoms

Life cycle diagrams for pennate (3-3-33443. Left 3-3-33444.) And centric (3-3-33443. Right 3-3-33444.) Diatoms. 2n and n Is diploid and haploid stages respectively. Drawing from the site

After the sexual process, which takes only a few minutes, in both pennate and centric diatoms, 3–3–3311 is formed. zygote (inside a cell carrying an immovable gamete or egg), which is called auxospore . It becomes covered with a denser shell and eventually turns into a normal vegetative cell.

Carapace of diatoms

Centric diatom Melosira sp., Forming filamentous colonies. Focus on the cell that has become an auxospore. View from the girdle. Photo through a light microscope from the site

The diversity of diatoms is enormous: according to scientists, the number of species is about 10-12 thousand, but some believe that they are an order of magnitude more. They belong to department ocrophyte algae 3-3-33440. and capable of photosynthesis of . Their carapace is transparent and completely does not interfere with the light penetrating into the cell. Algae in the form of phytoplankton emit more than 60% of the oxygen produced on the planet as a result of photosynthesis, and diatoms produce up to 20% of this amount due to the high rate of reproduction. At the same time, algae spend much less oxygen on their own breath than plants.

Carapace of diatoms

Colonial diatom Licmophora phlabellata . In colonial diatoms, daughter cells after vegetative division do not diverge, but remain connected. Here, a single cell is a section of a “fan”; this alga also has mucous legs, with which it is attached to the substrate. Darkfield microscopy, magnification 10x. Photo © Dr. Wim van Egmond from

The shell of the diatoms does not decompose, which allows a very detailed study of the paleontology of these algae. The most ancient fossils found belong to Cretaceous 3-3-33440. so that the age of the class is at least 150 million years. Diatoms form thick deposits, called diatomite .

Carapace of diatoms

Fossil centric diatom 3-3-33391. Triceratium morlandii from New Zealand diatomite, age 32–40 Ma. Phase contrast microscopy 3-3-33440. . Photo from the site

Diatomite is used as a raw material for the production of liquid glass, heat-insulating bricks, insecticides and fertilizers, as a polishing material (including it can be found in toothpastes). It is also part of some types of cement, used in concrete production, water filtration, etc. But nanotechnology has become a particularly promising area for the study of diatoms: scientists hope to learn how to influence the microstructure of the valves of these algae, for example, for use in medicine (see article 3-3-3405. Silicon nanotechnology in a 3-3-33440 test tube.).

Carapace of diatoms

A variety of diatoms in the form of a kaleidoscope. Darkfield microscopy . Photo from the site (be sure to follow the link, there are many beautiful photos)

Klaus Kemp, a well-known diatom specialist, even created real works of art by arranging various diatoms on coverslips as in a kaleidoscope.

Video about creating a kaleidoscope from different types of diatoms

Photo © Massimo Brizzi from , magnification 1600x.

Veronika Khityaev

22 май 2020 /
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