Table of contents:
- Place of amoeba in scientific classification
- School taxonomy
- Features of amoebas
- Internal structure of the amoeba
- Amoeba movement and digestion
- Excretory system and reproduction
Video: Common Amoeba Type - Size And Classification Of Common Amoeba
2023 Author: Riley Dean | [email protected]. Last modified: 2023-05-24 12:07
Last updated 18 March 2020 at 00:35
Reading time: 6 minutes
The naturalist scientist Levenguk, once discerning an amoeba in a drop of water through his microscope, called it an animacula, "a little animal." Since then, biologists have broken many copies, trying to determine what type of living creatures this representative of the mysterious microworld belongs to. After all, all life on Earth can be classified according to various criteria: by its external form, by its internal structure, by the way of nutrition or reproduction. On the one hand, this unicellular creature is capable of performing all the basic functions inherent in representatives of the animal world. On the other hand, its differences from animals and plants are very striking.
- 1 Place of amoeba in scientific classification
- 2 School taxonomy
- 3 Features of amoebas
- 4 Internal structure of the amoeba
- 5 Movement of amoeba and digestion
- 6 Excretory system and reproduction
- 7.1 Amoeba proteus
- 7.2 Entamoeba histolytica
- 7.3 Amoeba and immortality
- 7.4 Similar articles
Place of amoeba in scientific classification
From school, many remember well that this single-celled organism belongs to the simplest. Consider which kingdom the amoeba belongs to. Confusion often arises on this issue.
According to the taxonomic classification of living organisms, biologists currently distinguish five kingdoms:
The kingdoms of plants and animals are represented by multicellular organisms. Mushrooms make up a separate kingdom. The bacteria are classified as scraps. Amoeba belongs to the kingdom of protists, where it is included among the other protozoa (Protozoa).
Like amoeba, bacteria are made up of one cell. The difference is that bacteria lack a formalized cell nucleus; DNA is scattered throughout the cell. Amoeba, like other protists, has a nucleus.
In school biology, a different classification is adopted. According to it, the protozoa, including the amoeba, enter the animal kingdom, forming a separate sub-kingdom
The figure shows the classification of the common amoeba from the position of school systematics.
Amoebae belong to the class of rhizomes, which is subordinate to the type of sarco-flagella. That, in turn, enters into the sub-kingdom of the simplest.
The name "rhizomes" reflects the mode of movement common to representatives of this class
Features of amoebas
The body-cell is filled with jelly-like cytoplasm and looks arbitrary, that is, every time it looks different. But this is true as long as the amoeba is motionless. Having started to move, it takes on a well-defined shape, characteristic of its species. According to this form, protozoologists determine to which species a given protozoan belongs.
The size of the amoeba is from 1/5 mm. The largest of them is Amoeba proteus, its length reaches 600 microns (0.6 mm).
Behavior determines irritability and taxis - reactions in response to the action of chemical and physical agents, which biologists consider the rudiments of the nervous system. In response to stimuli, the body carries out the simplest motor reactions. For example, an amoeba crawls away from the light, feeling food - it moves towards it. That is, a positive taxis follows in response to a positive stimulus - food. The body responds with a negative taxis to light and chemicals.
The body is capable of regeneration. If the body is damaged in some place, it will be completed, provided the core is intact.
Internal structure of the amoeba
The body of an amoeba is a cell filled with cytoplasm. In the center is the nucleus, it contains genetic information intended for reproduction. The shape of the body is unstable, since the cell is not surrounded by a hard shell.
The parts of the body, or "organs" of the protozoa are called organelles. They perform various functions that ensure the vital activity of the body
- cell membrane;
- contractile and digestive vacuoles;
A thin cell membrane separates the contents of the cell from the external environment. The cytoplasm is divided into two layers: ectoplasm and endoplasm. Ectoplasm is the outer layer; it participates in the mechanism of cell movement. In the endoplasm, the inner layer of the cytoplasm, which is less dense than the ectoplasm, there are the nucleus and organelles, and also globules - fat droplets. They give the microorganism buoyancy. There are other granules that contain polysaccharides, crystals and other storage substances. Vacuole cavities are filled with cell sap; they perform digestive and excretory functions. The organs of movement of the amoeba - pseudopods - also serve to capture food.
Amoeba movement and digestion
The amoeba moves with the help of pseudopodia, which are protrusions of the cytoplasm. The creeping microorganism pulls the pseudopod in the right direction, and its entire body, as it were, smoothly "flows" into it. The movement of the amoeba looks like a squeezing and pulling process.
Amoeba is a predator. She eats and drinks, grabbing food with the help of the same pseudopods. The absorption of solid particles is called phagocytosis, while droplets with liquid are called pinocytosis. Sensing a particle of food nearby, the pseudopods grab it and push it into the cytoplasm. Then this particle is surrounded by a digestive vacuole, and with the help of enzymes it digests. The cytoplasm absorbs nutrients, the rest is excreted.
The characteristic type of nutrition for the amoeba, the kingdom of the protozoa, is endocytosis, that is, the capture of nutrient material by the cell
Some species feed on decaying organic material.
In the photo: what an amoeba looks like that has absorbed a diatom
Excretory system and reproduction
Isolation is carried out in two ways: through the ectoplasm or using a contractile vacuole. The digestive vacuole merges with the cell wall, and through it undigested residues are thrown out. The contractile vacuole contains excess fluid. Periodically, it contracts and pushes the liquid away.
The amoeba breathes with the entire surface of the body
Reproduction is asexual. The cell simply divides in two. By successive divisions, many individuals are formed. This way of self-reproduction is called binary fission. The whole process takes about 30 minutes.
Before division, the contractile vacuole and excretory organelle disappear. The cell stops moving. First, the nucleus is divided, then cytokinesis occurs: the body is divided in half, each half receives the same set of chromosomes and organelles.
The most famous is Amoeba proteus, or ordinary (Ukrainian Amoeba zvichayna, Latin Amoeba proteus Latin). In this name, the changing shape of the body of this creature was twice reflected: the ancient Greek sea god Proteus could take on various forms, and the word "Amoeba" itself means "change".
The figure shows several types.
Dysenteric amoeba and Fowler's nigleria are dangerous to humans. The first parasitizes in the human large intestine, causing chronic diarrhea. The second affects the brain, causing the most dangerous disease - amoebic meningoencephalitis. Another representative of the simplest - the oral amoeba - causes trouble for a quarter of the human population of the earth. It lives in carious teeth and crypts of the palatine tonsils, and, according to some researchers, is involved in periodontal diseases.
Other representatives: euglyph, arcella and armor difflugium.
Let us consider in more detail two types of amoeba: free-living Amoeba proteus and parasitic dysentery Entamoeba histolytica.
It inhabits fresh and stagnant water bodies. The most favorable environment for it are rotting ponds and swamps, where there are many bacteria. When living conditions become unfavorable, the individual surrounds itself with a cyst - a hard shell that protects it for a long time, and stops feeding. In cysts, the microorganism retains its viability for a long time. When times are better, the amoeba comes out of the cyst and returns to its usual way of life.
The common amoeba according to systematics belongs to sarcodes (rhizomes) and is their classic representative
Despite the "ordinariness", its feature is the presence of a huge number of chromosomes in the nucleus, more than 500.
The free-living protozoan Amoeba proteus is a completely full-fledged organism capable of independent existence.
One of the main characteristics of the common amoeba is the ability to form numerous pseudopods, up to 10, with the help of which it moves at a speed of up to 15 mm per hour.
Entamoeba is smaller than common. The pseudopods are shorter and wider.
It is a parasite that lives in the intestines. It feeds on bacteria, but also phagotes erythrocytes. A person becomes infected by swallowing his cysts.
In the intestine, Entamoeba multiplies without destroying the organ; at the same time, a person is a carrier. If the parasite invades the wall of the colon and begins to divide there, ulcers form, amoebic dysentery develops.
When feces thicken, cysts are formed. Once in the external environment, they can live in a humid environment for about a month.
Entamoeba is able to reproduce by forming cysts with multiple nuclei. As a result of mitotic division, 4-8 young individuals appear inside the cyst.
Different types of amoebas are able to change the size, diet and mode of reproduction depending on the conditions of existence: this manifests the evolutionary power of the simplest organisms
Amoeba and immortality
The capacity for endless existence is one of the most exciting features of the unicellular organism. Reproducing itself by dividing in half, each daughter cell is at the same time a parent. Each of the individuals turns out to be the same organism that existed in those distant times when the very first amoeba appeared on Earth. In this sense, biologists consider her to be immortal.
It is believed that her cell is not subject to apoptosis (programmed death). However, you can never say for sure how long an amoeba lives, more precisely, how long it can live. Once in an unfavorable environment, she will die like a mere mortal. Freshwater amoeba in salt water will lose its moisture, shrink and die. If she is exposed to any amoebicide such as tinidazole, she will also die.
In any case, experiments carried out back in the 60s of the last century show that in a favorable environment, with sufficient nutrition, this creature can live indefinitely. There have been no refutations of this fact yet.