Microscopic structure. Both cell layers of the hydra consist predominantly of so-called epithelial-muscle cells. Each of these cells has its own epithelial part and a contractile process. The epithelial part of the cell faces either outward (in the ectoderm) or toward the gastric cavity (in the endoderm).
Contractile processes extend from the base of the cell adjacent to the supporting plate - the mesoglea. Inside the contractile process are muscle fibers. The contractile processes of ectoderm cells are located parallel to the axis of the body and the axes of the tentacles, i.e., along the body of the hydra; their contraction causes shortening of the body and tentacles. The contractile processes of endoderm cells are located across the body in a circular direction; their contraction causes a narrowing of the hydra body. On the free surface of endoderm cells there are flagella, most often 2, and sometimes pseudopodia may appear.
In addition to epithelial-muscle cells, the ectoderm and endoderm contain sensory, nerve and glandular cells.
The former occupy the same position as epithelial-muscle cells, i.e., one pole extends to the surface of the body or to the digestive cavity, and the other to the supporting plate.
Hydra . I - in a calm state; II - contracted after irritation
The second lie at the base of the epithelial-muscle cells, near their contractile processes adjacent to the supporting plate. Nerve cells connected by processes into a primitive nervous system of a diffuse type. Nerve cells are especially numerous around the mouth, on the tentacles and on the sole.
Microscopic structure of hydra . I - incision through the body wall; II - diffuse nervous system (connections of nerve cell processes with each other are visible); III - separate epithelial-muscular cell ectoderm:
1—stinging cells, 2—epithelial-muscular cells of the ectoderm, 3—epithelial-muscular cells of the endoderm, 4—glandular cells of the endoderm, 5—flagellate and pseudopodial outgrowths of endoderm cells, 6—interstitial cells, 7—sensitive cells of the ectoderm, 8—sensitive ectoderm cells, 9—nerve cells of the ectoderm (nerve cells of the endoderm are not shown), 9 (III)—cell body, 10—contractile processes with contractile fibril inside them (11)
Glandular cells of the ectoderm are located mainly on the sole and tentacles; their sticky secretions on the sole serve to attach the hydra to the substrate, and on the tentacles they play a role in moving the animal (see below). The glandular cells of the endoderm are located near the mouth; their secretion has digestive value.
The ectoderm also contains stinging cells, i.e. cells containing stinging capsules (see above), they are especially numerous on the tentacles. Hydra has four types of stinging cells: the largest pear-shaped ones are penetrants, the small pear-shaped ones are volventes, the large cylindrical ones are glutinants, or streptolins, and the small cylindrical ones are stereolins. The effects of these types of capsules vary; Some of them, with their sharp threads, can pierce the wall of the enemy’s or victim’s body and introduce a toxic substance into the wound and thereby paralyze it, while others only entangle the victim with threads.
Finally, the hydra has undifferentiated so-called interstitial cells, from which various cellular elements of the hydra develop, in particular germ cells.
More interesting articles
The freshwater hydra is an amazing creature that is not easy to spot due to its microscopic size. Hydra belongs to the phylum of coelenterates.
The habitat of this small predator is rivers, dams, and lakes without strong currents overgrown with vegetation. The easiest way to observe a freshwater polyp is through a magnifying glass.
It is enough to take water with duckweed from a reservoir and let it stand for a while: soon you will be able to see the elongated “wires” of white or brown color 1-3 centimeters in size. This is exactly how the hydra is depicted in the drawings. This is exactly what a freshwater hydra looks like.
Structure
The hydra's body is tubular in shape. It is represented by two types of cells - ectoderm and endoderm. Between them there is an intercellular substance - mesoglea.
In the upper part of the body you can see a mouth opening framed by several tentacles.
On the opposite side of the “tube” there is a sole. Thanks to the suction cup, it attaches to stems, leaves and other surfaces.
Hydra ectoderm
Ectoderm is the outer part of the cells of an animal's body. These cells are essential for the life and development of the animal.
The ectoderm consists of several types of cells. Among them:
- skin-muscle cells - they help the body move and wriggle. When the cells contract, the animal contracts or, on the contrary, stretches. A simple mechanism helps the hydra move unhindered under the cover of water using “somersaults” and “steps”;
- stinging cells - they cover the walls of the animal’s body, but most concentrated in the tentacles. As soon as small prey swims near the hydra, it tries to touch it with its tentacles. At this moment, the stinging cells release “hairs” containing poison. Paralyzing the victim, the hydra attracts it to its mouth and swallows it. This simple scheme allows you to easily obtain food. After such work, the stinging cells self-destruct, and new ones appear in their place;
- nerve cells. The outer shell of the body is composed of star-shaped cells. They are connected to each other, forming a chain of nerve fibers. This is how the nervous system of an animal is formed;
- germ cells are actively growing in autumn period. They are egg (female) reproductive cells and sperm. The eggs are located near the mouth opening. They grow quickly, consuming nearby cells. Spermatozoa, after maturation, leave the body and float in water;
- intermediate cells - they serve defense mechanism: when an animal’s body is damaged, these invisible “defenders” begin to actively multiply and heal the wound.
Hydra endoderm
The endoderm helps the hydra digest food. Cells line digestive tract. They capture food particles, delivering them to the vacuoles. The digestive juice secreted by the glandular cells processes the beneficial substances necessary for the body.
What does hydra breathe?
Freshwater hydra breathing outer surface body, through which the oxygen necessary for its life is supplied.
In addition, vacuoles also participate in the respiration process.
Features of reproduction
In the warm season, hydras reproduce by budding. This is an asexual method of reproduction. In this case, a growth forms on the body of the individual, which increases in size over time. Tentacles grow from the “bud” and a mouth is formed.
During the budding process, a new creature separates from the body and goes free swimming.
During the cold period, hydras reproduce only sexually. Eggs and sperm mature in the animal's body. Male cells, having left the body, fertilize the eggs of other hydras.
After the reproductive function, adult individuals die, and the fruit of their creation becomes zygotes, covered with a dense “dome” in order to survive the harsh winter. In the spring, the zygote actively divides, grows, and then breaks through the membrane and begins an independent life.
What does hydra eat?
The hydra's diet is characterized by a diet consisting of miniature inhabitants of reservoirs - ciliates, water fleas, planktonic crustaceans, insects, fish fry, and worms.
If the prey is small, the hydra swallows it whole. If the prey is large in size, the predator is able to open its mouth wide and significantly stretch its body.
Regeneration of Hydra vulgaris
G Hydra has a unique ability: she does not age. Each cell of the animal is renewed in a couple of weeks. Even having lost a part of the body, the polyp is able to grow exactly the same one, restoring symmetry.
A hydra cut in half does not die: a new creature grows from each part.
Biological significance of freshwater hydra
Freshwater hydra is an indispensable element in food chain. This unique animal plays an important role in cleaning water bodies, regulating the population of its other inhabitants.
Hydras are a valuable research object for scientists in the biological, medical and scientific fields.
>>Features of the internal structure of the hydra
§ 8. Features of the internal structure of the hydra
The inner layer of cells is the endoderm.
Question 1. What are the features of the external structure of the hydra?
Hydra is an elongated sac-shaped polyp, reaching 1.5 cm in length. It is attached to the substrate by a sole located at one end of the body. At the other end there is a mouth opening surrounded by a corolla of tentacles. The body wall of the hydra is formed by two layers of cells: the outer - ectoderm and the inner - endoderm.
Question 2. How is the ectoderm of coelenterates structured?
Several types of cells can be distinguished in the ectoderm. The bulk is represented by epithelial-muscle cells that have processes in which contractile elements are concentrated. Also in the ectoderm are sensory, nervous, glandular, stinging and intermediate cells. Sensitive cells are located in the same way as epithelial-muscular cells, i.e., one end faces 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 participate in regeneration. Sex cells are formed in the ectoderm.
Question 3. What type nervous system do coelenterates have?
Coelenterates have diffuse type nervous system. Sensitive cells are located in the same way as epithelial-muscular cells, i.e., one end faces 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, the excitation that arises in the primary cells quickly spreads throughout the entire nervous network and the animal responds to the irritation by contracting the processes of the epithelial-muscle cells.
Question 4. How does a hydra stinging cell work?
The largest number of stinging cells are 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 throws out the thread it contains, which turns out like the finger of a glove. Burning or poisonous contents are released along with the thread. Thus, hydroids can immobilize and paralyze fairly large prey, such as cyclops or daphnia. Stinging cells after use they are replaced with new ones.
Question 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 processes resembling pseudopodia. Glandular cells secrete digestive enzymes into the digestive cavity: greatest number such cells are located near the mouth.
Question 6. Tell us about the nutrition of hydra.
Hydra is a predator. It feeds on plankton - ciliates, small crustaceans (cyclops and daphnia). The stinging threads entangle the prey and paralyze it. Then the hydra grabs it with its tentacles and directs it into the mouth opening.
Question 7. How is the hydra’s digestion process carried out?
Digestion in hydras is combined (intracavitary and intracellular). Swallowed food enters the digestive cavity. First, the food is processed with enzymes and crushed in the digestive cavity. The food particles are then 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, along with undigested food debris, they are thrown into the digestive cavity. environment through the mouth opening.
Question 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 ensure the restoration of body parts when damaged - regeneration.
Question 9. What is hermaphroditism?
Hermaphroditism is the simultaneous presence of both male and female organs in one organism.
Question 10. How does hydra reproduce and develop?
Hydra reproduces asexually and sexually. At asexual reproduction, which occurs during a period favorable for life, one or more buds are formed on the body of the mother’s body, which grow, their mouth breaks through and tentacles form. Daughter individuals are separated from the mother. Hydras do not form real colonies. Sexual reproduction occurs in the fall. 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 current of water. After fertilization, the zygote forms a shell, turning into an egg. The maternal organism dies, and the shell-covered egg overwinters and begins development in the spring. The embryonic period includes two stages: cleavage and gastrulation. After this, the young hydra leaves the egg shells and goes outside.
Question 11. What are hydromedusae?
Hydromedusae are free-swimming sexual specimens of some representatives of the hydroid class; they are formed by budding.
Question 12. What is a planula?
Planula is a larva covered with cilia. Formed after fertilization in some hydroids. Attaches to underwater objects and gives rise to a new polyp.
Question 13. What is it like? internal structure coral polyp?
Coral polyps have all characteristic features coelenterates. The body of coral polyps has the shape of a cylinder. They have a mouth surrounded by tentacles leading into a 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 allowing the polyp to change its body shape. Characteristic feature Coral polyps are characterized by the fact that most of them have a hard calcareous skeleton or a skeleton consisting of a horn-like substance.
Question 14. What role do coelenterates play in nature?
Coelenterates are predators and occupy a corresponding niche in food chains reservoirs, seas and oceans, regulating the number of single-celled, small crustaceans, worms, etc. Some deep-sea species of jellyfish feed on dead organisms. Coral polyps, which live in shallow tropical seas, form the basis of reefs, atolls and islands. These corals play an important role in coastal communities that include significant numbers of animals and plants.
The solution book contains answers to questions from the educational publication and is designed in an easy-to-read format. PDF format.
Lesson equipment.
Table “Freshwater Hydra”, multimedia projector, presentation “Freshwater Hydra”, microscopes, “Hydra” microslide.
Updating knowledge.
Learning new material
Introductory word from the teacher.
More than two and a half centuries ago, a young man came to Holland from Switzerland. He has just completed his university education in science. Needing money, he decided to hire himself as a tutor to a certain count. This work left him time to conduct his own research. The young man's name was Abraham Tremblay. His name soon became known throughout enlightened Europe. And he became famous by studying what was literally under everyone’s feet - very simple organisms that lived in puddles and ditches. Tremblay mistook one of these living creatures, which he carefully examined in droplets of water scooped up from a ditch, for a plant.
Application . Slide 3.4.
Freshwater hydra belongs to the phylum Coelenterate animals. Among the representatives of the type of coelenterates living in the seas, there are sessile forms - polyps and free-swimming ones - jellyfish. Freshwater hydra is also a polyp.
Write down the classification of the species “Freshwater Hydra”.
Application. Slide 5
External structure of the hydra
The hydra's body in the form of a thin oblong sac, only 2–3 mm to 1 cm long, is attached to a plant or other substrate with its lower end. The lower part of the body is called the sole. At the other end of the hydra’s body there is a mouth surrounded by a corolla of 6–8 tentacles.
Working with microspecimens. Consider the external structure of the hydra.
Application. Slide 6, 7
Draw the external structure of the hydra in a notebook and label the body parts.
Cellular structure of hydra
The body of the hydra has the form of a sac, the walls of which consist of two layers of cells: the outer - ectoderm and the inner - endoderm. Between them there are poorly differentiated cells. The cavity formed by this sac is called the intestinal cavity.
Application. Slide 7, 8, 9.
Filling out the diagram “Ectoderm cells”
We work independently. Fill out the diagram “Entodermal Cells”
What vital processes are characteristic of living organisms?
Application. Hydra movement. Slide 13, 14.
The structure of the nervous systems. Irritability.
Application. Slide 15,16.
Nutrition
Hydra is an active predator. Abram Tremblay said this while observing the hydra.
If the hydra is hungry, its body extends to its full length and the tentacles hang down. Food swallowed by the hydra irritates the sensitive cells of the endoderm. In response to irritation, they secrete digestive juice into the intestinal cavity. Under its influence, partial digestion of food occurs.
Application. Slide 17, 18.
Reproduction
Hydra reproduces sexually and asexually (budding). It usually buds in the summer. By autumn, male and female reproductive cells are formed in the hydra's body, and fertilization occurs.
Application. Slide 19, 20, 21.
Regeneration
On September 25, 1740, Abraham Tremblay cut the hydra in two. Both parts continued to live after the operation. From one piece, called Tremblay's "head", a new body grew, and from the other - a new "head". 14 days after the experiment, two new living organisms emerged. Hydra is small, only 2.5 centimeters. Such a small creature was divided into a hundred pieces - and from each piece a new hydra emerged. They split it in half and prevented the halves from growing together - they got two animals interconnected with each other. The hydra was dissected into bundles - a bundle-shaped colony of hydras was formed. When several hydras were cut and the individual parts were allowed to grow together, the result was absolutely monsters: organisms with two heads and even several. And these monstrous, ugly forms continued to live, feed and reproduce! One of Tremblay's most famous experiments is that, with the help of a pig's bristle, he turned the hydra inside out, that is, its inner side became outer; after that the animal lived as if nothing had happened.
Application. Slide 22, 23, 24.
Consolidation.
Choose the correct statements.
1. Among coelenterate animals there are representatives with radial and bilateral body symmetry.
- All coelenterates have stinging cells.
- All coelenterates are freshwater animals.
The outer layer of the body of coelenterates is formed by dermal-muscular, stinging, nerve and intermediate cells. - The movement of the hydra occurs due to the contraction of the stinging threads.
- All coelenterates are predators.
- Coelenterates have two types of digestion – intracellular and extracellular.
- Hydras are not able to respond to stimuli.
2. Name the characteristic features of freshwater hydra.
3. Fill out the table.
4. Fill in the missing words in the sentences.
The hydra is attached... to the substrate, at the other end is..., surrounded by.... Hydra... organism. Its cells are specialized, form... layers. Between them is... . A distinctive feature of coelenterates is the presence of... cells. There are especially many of them on... and around the mouth. The outer layer is called..., the inner layer.... Through the mouth, food enters... the cavity.
Homework.
- Study the paragraph.
- Repeat the signs of coelenterates.
- Prepare reports on coelenterate animals (jellyfish, corals, sea anemones).
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