intermediate cells. The musculoskeletal system of the cell. Intermediate cell filaments What are intermediate cells what are the hydra functions

Answers to school textbooks

Hydra is a sac-like elongated polyp, reaching 1.5 cm in length. It is attached to the substrate with a sole located at one end of the body. At the other end is a mouth opening surrounded by a rim of tentacles. The body wall of the hydra is formed by two layers of cells: the outer one is the ectoderm and the inner one is the endoderm.

2. How is the ectoderm of coelenterates arranged?

Several types of cells can be distinguished in the ectoderm. The bulk is represented by epithelial-muscular cells that have processes in which contractile elements are concentrated. Also in the ectoderm are sensitive, nervous, glandular, stinging and intermediate cells. Sensitive cells are located in the same way as epithelial-muscular cells, i.e., one end is turned outward, and the other is adjacent to the basement membrane. Nerve cells lie between the contractile processes on the basement membrane. Intermediate cells are undifferentiated cells from which specialized cells subsequently develop, in addition, they are involved in regeneration. Sex cells are formed in the ectoderm.

3. What type of nervous system do coelenterates have?

Coelenterates have a diffuse type of nervous system. Sensitive cells are located in the same way as epithelial-muscular cells, i.e., one end is turned outward, and the other is adjacent to the basement membrane. Nerve cells lie between the contractile processes on the basement membrane. If you touch the hydra, then the excitation that has arisen in the primary cells quickly spreads throughout the entire nervous network, and the animal responds to irritation by contracting the processes of the epithelial-muscular cells.

4. How is the hydra's stinging cell arranged?

The largest number of stinging cells is located in the tentacles. Inside the cell there is a stinging capsule with a poisonous liquid and a spirally coiled hollow thread. On the surface of the cell there is a sensitive spine that perceives external influences. In response to irritation, the stinging capsule ejects the thread it contains, which turns out like a finger of a glove. Burning or poisonous contents are released along with the thread. Thus, hydroids can immobilize and paralyze rather large prey, such as cyclops or daphnia. Stinging cells are replaced with new ones after use.

5. What cells form the inner layer of the hydra?

The cellular elements of the endoderm are represented by epithelial-muscular and glandular cells. Epithelial muscle cells often have flagella and outgrowths resembling pseudopodia. Glandular cells secrete digestive enzymes into the digestive cavity: the largest number of such cells is located near the mouth.

6. Tell us about the nutrition of the hydra.

Hydra is a predator. It feeds on plankton - ciliates, small crustaceans (cyclops and daphnia). Stinging threads entangle prey and paralyze it. Then the hydra grabs her with tentacles and directs her into the mouth opening.

7. How is the process of digestion carried out in hydra?

Digestion in hydras is combined (intracavitary and intracellular). Swallowed food enters the digestive cavity. First, the food is processed by enzymes and crushed in the digestive cavity. Then the food particles are phagocytosed by epithelial muscle cells and digested in them. Nutrients diffusely distributed among all cells of the body. From the cells, metabolic products are released into the digestive cavity, from where, together with undigested food residues, they are released into the environment through the mouth opening.

8, What are intermediate cells, what are their functions?

Intermediate cells are undifferentiated cells that give rise to all other types of ecto- and endoderm cells. These cells provide restoration of body parts in case of damage - regeneration.

9. What is hermaphroditism?

Hermaphroditism is the simultaneous presence of both male and female organs in one organism (from the Greek Hermaphroditos - the son of Hermes and Aphrodite, a mythical bisexual creature).

10. How does hydra reproduce and develop?

Hydra reproduces asexually and sexually.

With asexual reproduction, which occurs during a period favorable for life, one or more kidneys are formed on the body of the mother's organism, which grow up, their mouth breaks out and tentacles are formed. Daughter individuals are separated from the mother. Hydra do not form true colonies.

Sexual reproduction occurs in autumn. Hydras are mostly dioecious, but there are also hermaphrodites. Sex cells are formed in the ectoderm. In these places, the ectoderm swells in the form of tubercles, in which either numerous spermatozoa or one amoeboid egg are formed. Spermatozoa, equipped with flagella, are released into the environment and delivered to the eggs by a stream of water. After fertilization, the zygote forms a shell, turning into an egg. The mother organism dies, and the egg covered with a shell overwinters and begins development in the spring. The embryonic period includes two stages: crushing and gastrulation. After that, the young hydra leaves the egg shells and comes out.

11. What are hydromedusas?

Hydromedusas are free-floating sexual individuals in some representatives of the hydroid class, they are formed by budding.

12. What is a planula?

Planula is a larva covered with cilia. It is formed after fertilization in some hydroids. Attaches to underwater objects and gives rise to a new polyp.

13. What is the internal structure of a coral polyp?

Coral polyps have all the characteristic features of coelenterates.

The body of coral polyps is cylindrical. They have a mouth surrounded by tentacles leading to the throat. The digestive cavity is divided into a large number of chambers, thereby increasing its surface and, consequently, the efficiency of food digestion. In the ecto- and endoderm there are muscle fibers that allow the polyp to change the shape of the body.

A characteristic feature of coral polyps is that most of them have a hard calcareous skeleton or a skeleton consisting of a horn-like substance.

14. What role do coelenterates play in nature?

Coelenterates are predators and occupy a corresponding niche in the food chains of reservoirs, seas and oceans, regulating the number of unicellular, small crustaceans, worms, etc. Some deep-sea species of jellyfish feed on dead organisms.

Coral polyps living in shallow waters in tropical seas form the basis of reefs, atolls and islands. These corals play an important role in coastal communities, which include a significant number of animals and plants.

Almost all living organisms are based on the simplest unit - the cell. You can find a photo of this tiny biosystem, as well as answers to the most interesting questions in this article. What is the structure and size of the cell? What functions does it perform in the body?

The cage is...

Scientists do not know the exact time of the appearance of the first living cells on our planet. In Australia, their remains were found 3.5 billion years old. However, it was not possible to accurately determine their biogenicity.

The cell is the simplest unit in the structure of almost all living organisms. The only exceptions are viruses and viroids, which are non-cellular life forms.

A cell is a structure that can exist autonomously and reproduce itself. Its dimensions can be different - from 0.1 to 100 microns or more. However, it is worth noting that unfertilized feathered eggs can also be considered cells. Thus, the largest cell on Earth can be considered an ostrich egg. In diameter, it can reach 15 centimeters.

The science that studies the characteristics of life and the structure of the cell of the body is called cytology (or cell biology).

Discovery and exploration of the cell

Robert Hooke is an English scientist who is known to all of us from a school physics course (it was he who discovered the law on the deformation of elastic bodies, which was named after him). In addition, it was he who first saw living cells, examining sections of a cork tree through his microscope. They reminded him of a honeycomb, so he called them cell, which means "cell" in English.

The cellular structure of plants was confirmed later (at the end of the 17th century) by many researchers. But the cell theory was extended to animal organisms only at the beginning of the 19th century. Around the same time, scientists became seriously interested in the contents (structure) of cells.

Powerful light microscopes made it possible to examine the cell and its structure in detail. They still remain the main tool in the study of these systems. And the advent of electron microscopes in the last century made it possible for biologists to study the ultrastructure of cells. Among the methods of their study, one can also single out biochemical, analytical and preparative ones. You can also find out what a living cell looks like - the photo is given in the article.

Chemical structure of the cell

The cell contains many different substances:

organogens;
macronutrients;
micro- and ultramicroelements;
water.

About 98% of the chemical composition of the cell are the so-called organogens (carbon, oxygen, hydrogen and nitrogen), another 2% are macronutrients (magnesium, iron, calcium and others). Micro- and ultramicroelements (zinc, manganese, uranium, iodine, etc.) - no more than 0.01% of the whole cell.

Prokaryotes and eukaryotes: the main differences

Based on the characteristics of the cell structure, all living organisms on Earth are divided into two kingdoms:

prokaryotes are more primitive organisms that have evolved;
eukaryotes - organisms whose cell nucleus is fully formed (the human body also belongs to eukaryotes).

The main differences between eukaryotic cells and prokaryotes:

larger sizes (10-100 microns);
method of division (meiosis or mitosis);
ribosome type (80S-ribosomes);
type of flagella (in the cells of eukaryotic organisms, flagella consist of microtubules that are surrounded by a membrane).

eukaryotic cell structure

The structure of a eukaryotic cell includes the following organelles:

nucleus;
cytoplasm;
golgi apparatus;
lysosomes;
centrioles;
mitochondria;
ribosomes;
vesicles.

The nucleus is the main structural element of the eukaryotic cell. It is in it that all the genetic information about a particular organism is stored (in DNA molecules).

Cytoplasm is a special substance that contains the nucleus and all other organelles. Thanks to a special network of microtubules, it ensures the movement of substances within the cell.

The Golgi apparatus is a system of flat tanks in which proteins constantly mature.

Lysosomes are small bodies with a single membrane, the main function of which is to break down individual cell organelles.

Ribosomes are universal ultramicroscopic organelles, the purpose of which is the synthesis of proteins.

Mitochondria are a kind of "light" cells, as well as its main source of energy.

Basic functions of the cell

The cell of a living organism is designed to perform several important functions that ensure the vital activity of this very organism.

The most important function of the cell is metabolism. So, it is she who breaks down complex substances, turning them into simple ones, and also synthesizes more complex compounds.

In addition, all cells are able to respond to external stimuli (temperature, light, and so on). Most of them also have the ability to regenerate (self-heal) through fission.

Nerve cells can also respond to external stimuli through the formation of bioelectrical impulses.

All of the above functions of the cell ensure the vital activity of the body.

Conclusion

So, a cell is the smallest elementary living system, which is the basic unit in the structure of any organism (animal, plant, bacteria). In its structure, the nucleus and cytoplasm are distinguished, which contains all the organelles (cellular structures). Each of them performs its specific functions.

Cell size varies widely - from 0.1 to 100 micrometers. Features of the structure and vital activity of cells are studied by a special science - cytology.

Class Hydroid, Class Scyphoid, Class Coral polyps

Question 1. Describe the features of the external structure and internal organization of the hydra.

The body wall of the hydra is formed by two layers of cells: the outer (ectoderm) and the inner (endoderm), between which there is a basement membrane. Inside is a digestive cavity, which also goes into the tentacles. Several types of cells can be distinguished in the ectoderm. The bulk is represented by epithelial-muscular cells that have processes in which contractile elements are concentrated. In addition to these cells, the ectoderm contains sensory, nerve, glandular, and stinging cells.

Question 2. How is the ectoderm of coelenterates arranged? What is the structure of the stinging cell of the hydra?

Sensitive cells are located in the same way as epithelial-muscular cells, i.e., one end is turned outward, and the other is adjacent to the basement membrane. Nerve cells lie between the contractile processes on the basement membrane. Intermediate cells are undifferentiated cells from which specialized cells subsequently develop, in addition, they are involved in regeneration. Sex cells are formed in the ectoderm.

Stinging (nettle) cells - a hallmark of the coelenterates - are distributed throughout the ectoderm, but there are especially many of them on the tentacles and around the mouth. The stinging cell has a capsule similar to a bubble, inside of which there is a hollow thread coiled in a spiral. On the surface of the cell there is a sensitive spine that perceives external influences. In response to irritation, the stinging capsule ejects the thread it contains, which turns out like a finger of a glove. Burning or poisonous contents are released along with the thread. Thus, hydroids can immobilize (paralyze) rather large prey, such as cyclops or daphnia, and also cause significant damage to enemies.

Question 3. What type of nervous system do coelenterates have?

Coelenterates have a diffuse type of nervous system. Sensitive cells are located in the same way as epithelial-muscular cells, i.e., one end is turned outward, and the other is adjacent to the basement membrane. Nerve cells lie between the contractile processes on the basement membrane. If you touch the hydra, then the excitation that has arisen in the primary cells quickly spreads throughout the nervous network and the animal responds to irritation by contracting the processes of epithelial-muscular cells.

Question 4. Describe the cells of the inner layer of the hydra.

The cellular elements of the endoderm are represented by epithelial-muscular and glandular cells. Epithelial-muscular cells often have flagella and outgrowths resembling pseudopodia. Glandular cells secrete digestive enzymes into the digestive cavity: the largest number of such cells is located near the mouth.

Question 5. Tell us about the nutrition of the hydra. How is the process of digestion carried out in hydra?

Digestion in hydras is combined (intracavitary and intracellular). Swallowed food enters the digestive cavity. First, the food is processed by enzymes and crushed in the digestive cavity. Then the food particles are phagocytosed by epithelial-muscular cells and digested in them. Nutrients diffusely distributed among all cells of the body. From the cells, metabolic products are released into the digestive cavity, from where, together with undigested food residues, they are released into the environment through the mouth opening.

Question 6. What are intermediate cells, what are their functions?

Intermediate cells are undifferentiated cells that give rise to all other types of ecto- and endoderm cells. These cells provide restoration of body parts in case of damage - regeneration.

Question 7. How does hydra reproduce and develop? What is hermaphroditism? What is a planula?

Hydra reproduces asexually and sexually.

Hermaphroditism is the simultaneous presence of both male and female organs in one organism (from the Greek Hermaphroditos - the son of Hermes and Aphrodite, a mythical bisexual creature).

Planula (novolat. planula, from lat. planus - flat), one of the larval stages of intestinal development. The body is oval, elongated or vermiform; consists of 2 layers. The outer (epithelial) layer - the ectoderm, is represented by flagellar cells, among which are epithelial-muscular, nerve and stinging cells. The inner layer (endoderm) limits the closed cavity of the intestine. Planula swims in the water column, then attaches to the bottom and passes into the next stage of development - the polyp.

Question 8. Why do you think hydromedusae and jellyfish proper are classified as different groups of coelenterates?

Hydromedusas are free-floating sexual individuals in some representatives of the hydroid class, they are formed by budding. They form special sex glands that produce germ cells. Fertilization and development of the egg takes place outside the mother's body. A larva covered with cilia emerges from the egg - a planula, which later attaches to underwater objects and gives rise to a new polyp.

Scyphoid jellyfish are represented by species that live only in the seas. They are much larger than hydromedusas; the cyanide umbrella, for example, can reach 2 m in diameter, and the length of the tentacles is 30 m. Therefore, they are classified as different groups of coelenterates.

Question 9. Why did the coelenterates get such a name?

The name coelenterates was given in connection with the existing intestinal, or gastric, cavity.

Question 10. What are the geographical and climatic conditions for the distribution of various coelenterates?

More than 9 thousand species of the leading exclusively introductory, mainly marine way of life, belong to the intestinal cavities.

Hydroids are widely distributed in fresh waters around the world. Freshwater hydras are often found on aquatic vegetation in slowly flowing reservoirs. A significant number of hydroid species live in the seas, where their small colonies arise.

All jellyfish are predators, but deep-sea species also feed on dead organisms. Fish fry sometimes find shelter in the umbrellas of large jellyfish. In Japan and China, the mesoglea of some jellyfish, such as Aurelia and Rapillema, is eaten. Aurelia is one of the most common scyphomedusas. It lives in almost all seas except the Caspian and Aral. Usually, after laying their eggs, jellyfish die off and are sometimes thrown ashore by waves in the form of gelatinous translucent discs.

Coral polyps are distributed almost throughout the world's oceans. As a rule, they live at shallow depths, however, species are known that live at a depth of more than 1 km, and some species can go down to 5–8 km.

Musculoskeletal system and its components as a cell frame provide resistance to external physical factors and, at the same time, are easily rebuilt and change the shape of the cell, participate in the regulation of hyaloplasmic flows and the movement of organelles.

To the components of the cell musculoskeletal function includes intermediate filaments, microfilaments, microtubules and their specialized derivatives (microvilli, stereocilia, cilia and flagella). The performance of almost all cellular functions is associated with the activity of these structures.

Intermediate filaments

Intermediate filaments built from fibrillar protein monomers. Their spatial design resembles the weaving of a rope with a thickness of about 8-10 nm. In the cell, they are localized in the form of a three-dimensional network mainly in the perinuclear region and are collected in bundles that are directed to the periphery of the cell. Here they are either part of desmosomes and hemidesmosomes (in the cells of epithelial tissues), or are sent to the processes of nerve cells. These parts of the cytoskeleton are characteristic of all types of cells, however, they are especially well developed in cells that experience mechanical stress, for example, in epidermal cells, muscle cells, and neurons. The group of intermediate filaments includes several related proteins, but these are usually different proteins in different cells.

In cells of mesenchymal origin (connective tissue, endothelial, blood cells), intermediate filaments composed of vimentin. In muscle cells, the intermediate filament protein is called desmin (in cross-striated muscle fibers, desmin filaments are part of the Z-lines). In neurons, intermediate filaments maintain the shape of the processes of nerve cells and fix transmembrane ion channel proteins. In the cells of the epidermis, intermediate filaments, binding to other proteins, form the horny substance, which is a powerful protective layer of the skin, impervious to many water-soluble compounds dangerous to the body. Finally, in all cells, the nucleus contains proteins of the nuclear plate (lamins). In contrast to the stable intermediate filaments of the cytoplasm, the layers of the nuclear lamina filaments are easily disassembled during mitotic cell division.

Main functions of intermediate filaments are: supporting, maintaining the shape of the cell, participating in the formation of intercellular connections such as desmosomes and hemidesmosomes, special functions in various types of cells.

Microfilaments and their derivatives

These are threadlike contractions education about 5 nm thick, consist of actin protein and are universal elements of the cytoskeleton. In the cytoplasm, actin microfilaments are located singly, or in the form of a grid and bundles, and on the inside of the plasmolemma they form a thickening - the cortical layer of the cell, or cortex. In the latter, actin filaments form a network with the help of binding (linker) proteins, one of which is filamin. The filaments of the actin cortex are fixed to the plasma membrane with the help of plasma membrane integral proteins - integrins. In specialized regions of the plasmalemma and adhesive contacts, actin can become a transmembrane protein.

actin in all cells filaments interact with a modified form of myosin, represented by a monomeric structure - minimyosin. Minimyosin is connected to cellular organelles and facilitates their transport, as well as the movement of vesicles along actin filaments. During the polymerization of actin microfilaments, local movements of the cytoplasm occur, which are necessary for cell movement.

Specialized derivatives microfilaments are microvilli and their compacted complexes - stereocilia. Microvilli are thin (0.1 µm) and long (about 1 µm) outgrowths of the apical (apical) part of cells. Inside each microvilli there is a bundle of actin microfilaments in the amount of 20-30. At one end, the filaments are attached to the top of the microvillus, and the lower part of the filaments is woven into the actin cortex. The filaments are connected into a bundle by transversely arranged protein molecules (ligaments) of fascin and fimbrin. The contractile protein minimyosin, which causes shortening and elongation of microvilli, was also found in microvilli.

Main Functions microfilaments are: maintaining the shape and stiffening the cell (carried out by the cortex); participation in the formation of intercellular connections, participation in transport processes - endo-, pino-, exocytosis (carried out by the cortex); participation in the processes of movement of cell organelles, transport and secretory vesicles (carried out by actin microfilaments with minimyosin associated with the surface of these structures) and in the formation of microvilli and stereocilia, in the formation of actomyosin contractile complexes specialized for muscle structures, as well as in the formation of a cellular constriction during cytotomy.

INTERMEDIATE CELLS

INTERMEDIATE CELLS, form a connective tissue between other tissues or groups of cells. For example, in nematocysts (such as jellyfish), they take the form of embryonic cells and fill the space between the cylindrical cells that form the body. In the testicles of vertebrates, interstitial cells between the seminiferous tubules produce male sex hormones - androgens.

Scientific and technical encyclopedic dictionary.

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