Protozoa are single-celled animals that can have one, two or more nuclei. Single-celled eukaryotes live in colonies and are considered the most numerous and oldest inhabitants of the earth. The simplest organisms with a nucleus appeared about 1.5 billion years ago. Living organisms without a nucleus appeared about 4 billion years ago.
Interesting information
Different types
- A tablespoon of sea sand is not so much, however, it contains 100-200 thousand shells of foraminifera - a marine protozoan.
- Euglena greena feeds on chlorophyll like a plant, but when unfavorable conditions For this type of nutrition, euglena can feed like an animal - on other creatures.
- Sporozoa is a protozoa that does not have any forms of movement.
- The body shape of amoebas is constantly changing, and the sizes can be very different. For example, the size of a small amoeba can be a quarter of a millimeter, and a large one 8 millimeters.
- Some microorganisms reproduce by division. Paramecia can divide up to three times a day.
- The protozoa Ciliates have a peculiar skeleton, which consists of polysaccharides.
- The flagellated microorganism Monas stigmatica is considered the fastest. This organism, which consists of one cell, can run a distance in one second that is forty times its length. If a person were that fast, he would cover more than 60 meters in one second.
- The empty shells of the rhizomes, which in ancient times lived in the sea, accumulated over many millions of years. It is from them that calcareous (sedimentary) rocks were formed. The chalk we use to write on the blackboard at school consists of the shells of these microorganisms.
Ciliate slipper
The ciliate slipper is an amazing predator:
- Among the protozoa there are also predators. Most famous representative single-celled predators - slipper ciliates. Ciliates feed on microbes through the mouth cavity, which sucks in water along with the microbes.
- The speed of movement of the ciliate slipper is approximately 10 times the size of its body per second.
- Not only microbes, but also other, smaller protozoa also have the risk of becoming dinner for ciliates.
The largest cell in the human body is the egg and, of course, it is found only in the body of women, since it is part of the female reproductive system. Its diameter is approximately 130 microns. It is commonly believed that an egg lives for about one month, but this is not true. A month is the time of its maturation. And the egg itself older women for 5-6 months. How can this be? The fact is that even when the little girl is in the womb, between the 3rd and 6th months of intrauterine development, all her eggs are formed.
A newborn girl is born with a full set of immature eggs. She has about 100,000 of them. Approximately 250-400 of them will mature during a woman’s life, only a few of them will be fertilized and make the world happy with a new birth. All the rest will remain in an immature state.
Egg of the expectant mother
Eggs are greatly influenced by life factors: infections, chronic diseases, stress, depression, smoking, alcohol, taking heavy medications, etc. All this cannot pass without leaving a trace and has a strong impact on the unborn child. By the way, the older a woman gets, the older her eggs are. At the same time, their risk increases genetic disorders. For example, for 30-year-old women, the risk of having a child with Down syndrome increases 4 times compared to 20-year-old women, and for 40-year-old women – 10 times.
According to doctors, women who want to give birth to a child after 35 years old should definitely consult a doctor, or even better, resort to the method of artificial insemination. It greatly reduces the chances of having a child with pathologies, since the egg is fertilized in the laboratory and is carefully examined for abnormalities even before it is implanted into the uterine cavity.
Description of sperm
The smallest cell in the human body is the sperm. It occurs only in men, because it is part of their reproductive system. The first sperm cells, like immature eggs in the body of women, are formed even when the unborn boy develops in the womb. The main vital task of the cell is to overcome the woman’s reproductive tract and penetrate the egg to fertilize it. Together with the sperm, the man's genetic material is introduced into the egg.
The total length of the cell is 55 µm, the head is 5.0 µm in length and 3.5 µm in width, the middle section is 4.5 µm and the tail is 45 µm in length. This small size allows the sperm to move quickly. The cell moves with the help of a flagellum, while it rotates around its axis. Movement speed 3 mm/min. To fertilize a female cell, a sperm needs to travel a distance of about 20 centimeters.
Fertilization of the egg
In a man’s body, a sperm matures within 64 days and can remain alive for about a month. After entering a woman’s body, sperm die within about 2 hours. Having reached the uterine cavity, sperm can live up to three days, and at the same time maintain their motor activity, since the cavity environment supports their vital activity. According to scientists, in the uterine cavity physical activity sperm even increases.
The sperm then move down the fallopian tube against the flow of fluid. How they can find the egg is not yet known to science. There is a possibility that they rush towards the source of enzymes that are secreted by the egg. With pathology in men, the quantity and quality of sperm decreases, this is often the cause of infertility. The quality of sperm is also significantly affected by the environment and lifestyle of a man.
Animals consisting of a single cell with a nucleus are called unicellular organisms.
They combine characteristics cells and independent organism.
Unicellular animals
Animals of the subkingdom Unicellular or Protozoa live in liquid environments. External forms they are varied - from amorphous individuals that do not have a definite outline, to representatives with complex geometric shapes.
There are about 40 thousand species of single-celled animals. The most famous include:
- amoeba;
- green euglena;
- ciliate-slipper.
Amoeba
It belongs to the rhizome class and is distinguished by its variable shape.
It consists of a membrane, cytoplasm, contractile vacuole and nucleus.
Assimilation nutrients carried out with the help of a digestive vacuole, and other protozoa, such as algae and etc., serve as food. For respiration, amoeba requires oxygen dissolved in water and penetrating through the surface of the body.
Green euglena
It has an elongated fan-shaped shape. It feeds by converting carbon dioxide and water into oxygen and food products thanks to light energy, as well as ready-made organic substances in the absence of light.
Belongs to the class Flagellates.
Ciliate slipper
A class of ciliates, its outline resembles a shoe.
Bacteria serve as food.
Unicellular fungi
Fungi are classified as lower non-chlorophyll eukaryotes. They differ in external digestion and chitin content in the cell wall. The body forms a mycelium consisting of hyphae.
Unicellular fungi are systematized into 4 main classes:
- deuteromycetes;
- chytridiomycetes;
- zygomycetes;
- ascomycetes.
A striking example of ascomycetes is yeast, which is widespread in nature. The speed of their growth and reproduction is high due to their special structure. Yeast consists of a single round cell that reproduces by budding.
Unicellular plants
A typical representative of lower unicellular plants often found in nature are algae:
- chlamydomonas;
- chlorella;
- spirogyra;
- chlorococcus;
- Volvox.
Chlamydomonas differs from all algae in its mobility and the presence of a light-sensitive eye that determines the location largest accumulation solar energy for photosynthesis.
Numerous chloroplasts are replaced by one large chromatophore. The role of pumps that pump out excess fluid is performed by contractile vacuoles. Movement is carried out using two flagella.
Green algae, Chlorella, unlike Chlamydomonas, have typical plant cells. A dense shell protects the membrane, and the cytoplasm contains the nucleus and chromatophore. The functions of the chromatophore are similar to the role of chloroplasts in land plants.
The spherical algae Chlorococcus is similar to Chlorella. Its habitat is not only water, but also land, tree trunks growing in a humid environment.
Who discovered single-celled organisms
The honor of discovering microorganisms belongs to the Dutch scientist A. Leeuwenhoek.
In 1675, he examined them through a microscope of his own making. The name ciliates was assigned to the smallest creatures, and since 1820 they began to be called the simplest animals.
Zoologists Kelleker and Siebold in 1845 classified unicellular organisms as a special type of the animal kingdom and divided them into two groups:
- rhizomes;
- ciliates.
What does a single cell animal cell look like?
Structure single-celled organisms can only be studied with a microscope. The body of the simplest creatures consists of a single cell that acts as an independent organism.
The cell contains:
- cytoplasm;
- organoids;
- core.
Over time, as a result of adaptation to environment, in certain species of unicellular organisms special organelles of movement, excretion and nutrition appeared.
Who are the protozoa?
Modern biology classifies protozoa as a paraphyletic group of animal-like protists. The presence of a nucleus in a cell, unlike bacteria, includes them in the list of eukaryotes.
Cellular structures differ from those of multicellular organisms. In the living system of protozoa, digestive and contractile vacuoles are present; some have organelles similar to the oral cavity and anus.
Protozoan classes
IN modern classification According to the characteristics, there is no separate rank and significance of unicellular organisms.
Labyrinthula
They are usually divided into the following types:
- sarcomastigophores;
- apicomplexans;
- myxosporidium;
- ciliates;
- labyrinthula;
- Ascestosporadia.
An outdated classification is considered to be the division of protozoans into flagellates, sarcodes, ciliates and sporozoans.
In what environments do unicellular organisms live?
The habitat of the simplest unicellular organisms is any humid environment. Common amoeba, green euglena and slipper ciliates are typical inhabitants of polluted fresh water sources.
The science for a long time classified opalines as ciliates, due to the external similarity of flagella to cilia and the presence of two nuclei. As a result of careful research, the relationship was refuted. Sexual reproduction opaline occurs as a result of copulation, the nuclei are identical, and the ciliary apparatus is absent.
Conclusion
It is impossible to imagine a biological system without single-celled organisms, which are the source of nutrition for other animals.
The simplest organisms contribute to the formation of rocks, serve as indicators of pollution of water bodies, and participate in the carbon cycle. Microorganisms have found widespread use in biotechnology.
Antonenko Andrey
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How many small creatures live on Earth, about which we know nothing. These creatures are both unicellular and multicellular. Multicellular creatures are larger in size than unicellular ones. That is why most of the smallest creatures on Earth are simplest organisms. This list contains the ten smallest organisms.
Sea Urchin Echinocyamus Scaber
In science, sea urchins are classified in the class Echinoidea. These creatures are found in the oceans and live even at depths of 5000 meters. These are very tiny creatures with a spherical shape and a spiny, round shell. There are sea urchins different colors, including blues, reds, purples, greens, olives and various shades of brown. They are characterized by great diversity - approximately 950 species sea urchins classified into this moment, and they all have different sizes, as well as shells ranging from 3 - 10 cm. These creatures move very slowly and depend on seaweed. Their smallest species is called Echinocyamus scaber - it does not exceed 6 mm in size, being one of the smallest creatures on Earth.
Starfish Patiriella Parvivipara
Starfish belong to the class Asteroidea. These creatures live in oceans around the world at depths of up to 6,000 meters or more. The shape of the starfish is somewhat like a star, with a round disk in the center, and five limbs surrounding it. Some star species have more than five limbs and come in a variety of colors, including red, blue, brown, orange, or grey colour. These creatures have the ability to regenerate limbs after being attacked by predators. The starfish feeds on a variety of prey and its life cycle quite complex. Many species of this creature have been discovered, but the smallest of them is Patiriella Parvivipara, measuring 5 mm. It is most often found near South Australia.
Sea cucumber Psammothuria Ganapati
Species of Sea Cucumbers are marine animals that belong to the class Holothuroidea. These varieties have an elongated body, slightly reminiscent of a cucumber - hence the corresponding name. The Sea Cucumber has a single sexual gland and is found in all of the world's oceans, but is most widespread in the Asia-Pacific region. These types of creatures are also eaten by people, they are even raised on special farms. Sea cucumbers send hormonal signals to communicate with other creatures of their species. The Sea Cucumber comes in a variety of sizes, ranging from 10 to 30 centimeters in length. However, the smallest one is called Psammothuria ganapatii and is approximately 4mm in length. You can meet this baby on the coast of India 
Beetle Scydosella Musawasensisis
Beetles are usually classified under the insect class and have two pairs of wings. These animals have the ability to survive in any environment. They are present everywhere, with the exception of marine and colder areas. These species can survive on any type of diet, including waste, fungi, plants, flesh and much more. Overall, there are more than forty thousand species of beetles worldwide, ranging in size, but the smallest of these species, Scydosella musawasensis of the genus Nanosellini, is only 300 micrometers in length. 
Nanoarchaeum bacterium
Nanoarchaeum equitans is a bacterium with a diameter of 400 nm. The body requires quite high temperature for your full height, and must always remain in contact with the owner. Small size at 400 nm makes them one of the smallest living creatures in the world. 
Nanobacterium Nanobes
The newly discovered nanobacterium Nanobes is one-tenth the size of bacteria and is considered the tiniest life form on earth. They reach only 20 millimicrons in size and are rather poorly studied. Until now, little is known about their unconventional method of reproduction, as well as other details of the functioning of Nanobes. 