"Diatoms" by kevin dooley is licensed under CC BY 2.0
Definition of Bacillariophyta (Diatoms)
Bacillariophyta or Diatoms are unicellular algae that are widely distributed in freshwater and seawater, as well as in moist soils. The number of diatoms is very large, it is estimated that there are 16,000 types. Due to the large number of diatoms, which act as one of the phytoplankton, they become an important producer component in marine waters.
Some diatoms live alone and some form colonies in filaments. Some live freely on the surface of the water, some other species live attached to the substrate. Bacillariophyta has food that is stored as leukocin in the form of oil drops and has photosynthetic pigments, namely chlorophyll a, chlorophyll c, xanthophyll, and carotene.
Diatom cells elongated shape with a cell wall or shell consisting of two parts like a box (hypotheka) with a lid (epiteka). The shell is composed of pectin and silica with various forms of ornamentation. When a diatom dies, a translucent silica shell remains. The shells of diatoms are equipped with tiny holes that allow the cell to come into contact with the water environment.
Diatoms have the highest abundance and can be found in various types of habitats such as wet soil, rock walls, steep coral, peat and bark. In addition, Diatoms can be seen as yellow froth on the mud in sewers or ponds. Thus it can be said that diatoms are cosmopolitan. Besides being cosmopolitan, diatoms also have a high growth rate, for example in fertile and unpolluted waters the population density can reach 2,000 – 10,000 cells per liter of water.
Factors Affecting Diatom Growth
■ Water is an essential for growth and development, as well as necessary at various stages of the life of diatoms. If there is no water, diatoms will not be able to survive much longer in the active state.
■ Light also includes an important factor that will determine the growth and development of the diatom. Light is the main component for the process of photosynthesis. Some diatoms are insensitive to light intensity. However, there is also a metabolic process that requires a certain light intensity. Therefore, appropriate light is needed for the process to run well.
■ The temperature is a factor that affects the presence of diatoms in the habitat. Each genus (Marga) of diatoms has a different optimum temperature. Certain species require a certain temperature range for normal metabolic processes. Above and below the optimum temperature range, metabolic processes will not take place normally and even die.
■ Organic compounds . The content of organic compounds dissolved in the waters greatly affects the level of acidity and alkalinity. Some diatoms require a pH below 7.00 and a low content of calcium (Ca) and Magnesium (Mg), for example Eunotia and Frustulia .
Other genera are just the opposite, avoiding acidic waters and very low concentrations of calcium and magnesium, such as Mastogoia, Diploneis, Amphipleura, Gysigma, Denticula , Ephitemia, and Rhopalopoada . Slight changes in the pH value and organic compounds of the waters will affect the presence of diatoms in these waters. Organic compounds for diatoms are useful in the formation of frustules, such as sulfur and calcium.
How Diatoms Move
Although it does not have a special means of locomotion, it does not mean that diatoms cannot move. According to Bold & Wynne, diatoms move spontaneously. This spontaneous movement occurs because of the following three things:
1. The presence of mucopolysaccharide chain secretion. This substance is secreted continuously, causing cells to move and be able to move places.
2. The existence of a capillary mechanism that causes the slow movement of the particles along the raphe.
3. The movement of diatoms is closely related to the flow of cytoplasm in the cell and the presence of raphes in the cell wall.
Body Structure of Bacillariophyta (Diatoms)
To understand how the structure or parts of diatom cells, we take the example of Pinnularia Viridis which is a species of Bacillariophyta. The body structure of Pinnularia sp. and its function is shown in the picture and description below.
Diatom cell walls are made of pectin and silica, so the structure is very hard. The cell wall consists of two parts called valves ( walves ) . This valve has 2 overlapping parts and is limited by a layer called the cingulum . The two parts of the valve together with the protoplast are called frustules . The outermost valve is called the epitheca while the smaller inner valve is called the hypotheca .
The surface of the valve has pores or short holes to form a pattern or mark on the valve part (wall marking) . Meanwhile, the part where there is no wall marking is called the axial area. Wall markings are arranged in a linear row. In the axial region, it may contain longitudinal slits called raphes . The raphe has a circular structure in the middle called a central nodule .
Characteristics of Bacillariophyta (Diatoms)
Diatoms or Bacillariophyta have general characteristics or characteristics, namely as follows.
■ Generally unicellular (single-celled) and live freely. However there are some members that form colonies in various forms such as filaments.
■ Types of eukaryotic cells because it already has a core membrane.
■ Characteristically autotrof being able to perform photosynthesis.
■ cells are microscopic in various shapes such as oval, round, triangular, ships and so forth.
■ Body bilaterally symmetrical or radially symmetrical.
■ Having a rigid cell wall made of pectin substances and silica.
■ Have a photosynthetic pigment chlorophyll a and chlorophyll c and santofil like fukosantin, diatosantin and diadinosantin.
■ Backup food is stored in the form of oil.
■ It is mostly berhabitat algae in freshwater and seawater.
Classification of Bacillariophyta (Diatoms)
The grouping of diatoms is based on two things, namely based on the way of life and shape. The following is an explanation of the two types of grouping Bacillariophyta or diatoms.
Classification of Diatoms Based on Shape
Based on their shape, diatoms are divided into centric (radial symmetry) and pennate (bilateral symmetry) forms .
■ Centris , talus shaped radial symmetry, no sliding movement occurs, sexual reproduction is anisogamy or Oogami, and gametnya motile.
■ Pennate , shaped talus bilateral symmetry, sliding movement occurs, and sexual reproduction in amoeboid.
Classification of Diatoms Based on Way of Life
Based on their way of life, diatoms are grouped into two major groups, namely benthic diatoms and planktonic diatoms.
■ Diatoms benthos generally live mixes with mud or attached to the substrate at the bottom, for example Cymbella, Gomphonema, Cocconeis, and Eunotia .
■ diatom plankton usually live freely floated in water, both freshwater and seawater. In fresh water diatoms can be found in rivers, lakes, ponds, swamps, and some can be found in waters where the temperature reaches 45 0 C. Some diatoms live as epiphytes in other algae or aquatic plants.
Methods of Reproduction of Bacillariophyta (Diatoms)
Reproduction in Bacillariophyta or diatoms can occur in two ways, namely asexually (vegetatively) by cell division and sexually (generatively) by oogamy.
Asexual reproduction of diatoms
Diatoms have a box-like shape and have a cell wall. The cell is composed of two parts, namely the container (hypotheca) and the lid (epiteka). If these cells divide, then initially between the container and the lid will separate. Next, each will form its own container and lid. So, the lid (epiteka) forms a new container (hypotheka) and the container part will form a new lid and have a smaller size.
Once formed, if the cell will divide again then the process is the same, and so on until over time the cells are so small that they cannot divide again. At a critical level of cell size and cell division is no longer possible, the protoplasm will come out of the cell wall and form auxospores . Auxospores will experience growth to improve cell size to normal. Subsequent reproduction is done sexually.
Sexual Reproduction of Diatoms
Sexual reproduction of diatoms occurs through oogamy in which non-motile egg cells fuse with motile male gametes. When the male gamete cell enters the egg cell, fertilization occurs and a zygote is formed.
Examples and Roles of Bacillariophyta (Diatoms) in Life
What is the role of diatoms in natural life? The role of diatoms is very important in aquatic ecosystems because they are producers in the food chain, namely as producers of organic matter and oxygen. In freshwater ecosystems, diatoms take over the role of other flora, especially Cyanophyta and Chlorophyta. Diatoms that live in the oceans have an important part in life, namely as a food source for colorless protists or small animals so that they can prolong the life of other organisms.
If this diatom dies, it will fall to the bottom of the sea, and because it contains silica, its cell walls will not be destroyed and remain intact. Large deposits of this material, known as diatomaceous earth, are found in many parts of the earth's surface. On United States soil, the largest assemblages 1,400 feet (or more than fifty meters) thick are in California.
Because diatomaceous earth is chemically inert and has outstanding physical properties, it is of great importance and industrial value. For example it is used as a filtering agent, which is widely used to separate colored substances from products such as gasoline and sugar. Because it is not a good conductor of heat, diatomaceous earth is used in heating pipes and steam pipes.
Diatom shells are also sound-absorbing, so they can be used as materials in soundproofing devices. In addition, it is used in the manufacture of paints, varnishes, vinyl records, and containers for battery boxes. Because of its hardness, it is also used in lubricants and abrasives.
In addition, it is also used as an insulating material, cosmetic base material, and dynamite insulation.
