The members of the division bacillariophyta are known as diatoms. Diatoms mean to cut into two. The name of these organisms is based on the cell wall of the diatoms that is divided into two parts. Diatoms belong to the kingdom Protista.
The Salient Features of the Protista Kingdom:
The living organisms included in this kingdom are as follows: dinoflagellates, diatoms, euglenoids, slime moulds, and protozoans.
All the organisms included in this kingdom are unicellular and eukaryotic in nature.
The mode of nutrition in protists is of different types:
Holophytic or Photosynthesis
These organisms can synthesize their own food. The synthesis of food can be done by the method of photosynthesis.
Holozoic Mode of Nutrition
These organisms possess a similar mode of nutrition as that of animals. In these organisms, the food is first ingested and then digested.
Some protists obtain their food from dead organic matter substances. These types of protists secrete some extracellular enzymes. These enzymes convert complex or compound substances into simple substances. These produced simple substances are easily absorbed by the body surface of the protists.
Mixotrophic Mode of Nutrition
Some protists have different types of mode of nutrition.
Mode of Reproduction
Protists reproduces both by sexual and asexual means of reproduction. Types of reproduction in protists are discussed below:
1. Asexual Reproduction
This is the most common method of reproduction in the members of the protist kingdom. Asexual reproduction takes place in favourable condition. It is of the following types:
In this type of reproduction two types of reproduction two daughter cells are formed by the division of one mother cell. After this step, each daughter cell formed in the binary fission grows in size to form a normal organism.
Some of the protists possess a special structure that is known as sporangia. Production of Spores takes place in this sporangia. The bursting of sporangia takes place after some time and all the spores become free (released into the environment). These spores form a new cell after germination.
2. Sexual Reproduction
In the sexual reproduction process two gametes (haploid in nature) fuse to form a zygote (diploid in nature). This fusion is known as syngamy. This fusion can be divided into three types.
The isogamy mode of fusion is the easiest way of sexual reproduction. In isogamy, the fusing gametes are morphologically similar but physiologically they may be similar or dissimilar.
The fusing gametes are morphologically dissimilar but physiologically they may be similar or dissimilar.
This type of fusion is developed from anisogamy. In this type of fusion, the male gamete is small and motile while the female gamete is large and non-motile. This female gamete is known as an egg. In it, the formation of male and female gametes takes place in sex organs.
Diatom is composed of two words Di and atoms that indicate two halves. The body of the diatom is divided into two halves. The scientific name of the diatom is Chrysophyta. The word Chrysophyta means golden colour. Therefore, diatoms are golden in colour. Diatoms are also known as golden algae. The cell structure of diatoms is unicellular. These organisms are eukaryotic in nature. They have the holophytic mode of nutrition because they possess chloroplast.
Division of Diatoms- Chrysophyta or Bacillariophyta.
Diatoms Under Microscope
Diatoms under a microscope can be easily visible. These organisms are not easily visible by the naked eye, thus need to view the diatoms under the microscope. Diatoms under the microscope make very interesting specimens. They have complex patterns on their surface with very fine punctures. Fine pores in the frustules of some of the animals are used to measure the resolving power of a microscope lens.
General Characteristics of Diatoms
Diatom is generally found in both freshwater and marine water.
The Shell of Diatom:
Diatom has silica in their shell wall. Their cell wall is called a shell or frustule. Diatoma has overlapping shell walls. The colour of the shell of the diatoms is generally transparent. The cell wall of these organisms is generally composed of cellulose. In this cellulosic cell wall, the silica particles are embedded in many places. Due to this reason, the cell wall appears to be made up of silica.
The Nucleus of the Diatom:
Diploid nucleus is present in the diatom.
Pigments Present in the Diatoms:
The cell wall of diatoms consists of chloroplasts. In the chloroplast of the diatoms, the pigments are present. These pigments are chlorophyll a, chlorophyll c, and xanthophyll. This xanthophyll is also known as fucoxanthin. Due to these pigments diatoms appear golden in colour.
Movement of the Diatoms:
Diatoms are immotile, because of the absence of flagella in them. They generally float on the surface of the water with the help of low molecular weight stored fats. The movement of some diatoms is done with the help of the slimy secretion. This slimy secretion is an oily material excreted by the diatoms. This provides the lubrication for the movement of the diatoms.
Mode of Nutrition in Diatoms:
The diatoms are autotrophic in nature. The form of stored food in the diatoms are leucosin (chrysolaminarin) and fats (oils).
The Shape of Diatoms:
The diatoms found in nature are of two types. One is round in shape and the other is elongated. On the basis of shape, diatoms can be classified into two types. These types are discussed below:
Types of Diatoms
Let us discuss these two forms one by one.
These types of diatoms are elongated in shape. These diatoms can be divided bilaterally. Therefore, they have bilateral symmetry. Pennate diatoms are motile in nature. They move by the gliding movement.
These types of diatoms are round-circular in shape. They possess radial symmetry. These forms of diatoms are non-motile in nature.
Reproduction in Diatoms
The diatoms reproduce both by sexual and asexual means. Diatoms mainly reproduce by the asexual mode of reproduction, by binary fission. Sexual reproduction is very rare in them. Sexually they reproduce by the gametic meiosis. The zygote formed during sexual reproduction is called auxospore. Auxospore is a asexual structure. When the diatoms reproduce by asexual means, their size decrease because of silica. To overcome this problem, they reproduce by the sexual mode of reproduction.
Use of Diatoms
Filtration of oils and syrups
As a heat insulator in steam boilers. They are used as thermostat because the kieselguhr is a bad conductor of electricity.
Diatoms are used as toothpaste.
Some diatoms are used in making skin medicines.
Diatoms are used in the manufacturing of certain medicines.
Diatoms are used as an insecticide, as they dry them by absorbing oil.
Did You Know That?
The cell wall of the diatoms has silica in very large quantities. Due to this reason, their cell wall is hard. The cell wall does not get destroyed after their death so, at the bottom of the sea, very huge rocks of dead diatoms are formed which are known as diatomite or diatomaceous earth or kieselguhr.
Diatoms are the chief producers in the ocean.
Diatoms are known as golden algae or jewels of the sea.