Figure: Structure of freshwater hydra. Radial symmetry of Hydra
Habitat, structural features and vital functions of the freshwater hydra polyp
In lakes, rivers or ponds with clean, transparent water, a small translucent animal is found on the stems of aquatic plants - polyp hydra(“polyp” means “multi-legged”). This is an attached or sedentary coelenterate animal with numerous tentacles. The body of an ordinary hydra has an almost regular cylindrical shape. At one end is mouth, surrounded by a corolla of 5-12 thin long tentacles, the other end is elongated in the form of a stalk with sole at the end. Using the sole, the hydra is attached to various underwater objects. The body of the hydra, together with the stalk, is usually up to 7 mm long, but the tentacles can extend several centimeters.
Radial symmetry of Hydra
If you draw an imaginary axis along the body of the hydra, then its tentacles will diverge from this axis in all directions, like rays from a light source. Hanging down from some aquatic plant, the hydra constantly sways and slowly moves its tentacles, lying in wait for prey. Since the prey can appear from any direction, the tentacles arranged in a radial manner are best suited to this method of hunting.
Radiation symmetry is characteristic, as a rule, of animals leading an attached lifestyle.
Hydra intestinal cavity
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). Inside the body of the hydra there is intestinal cavity(hence the name of the type - coelenterates).
The outer layer of hydra cells is the ectoderm.
Figure: structure of the outer layer of cells - hydra ectoderm
The outer layer of hydra cells is called - ectoderm. Under a microscope, several types of cells are visible in the outer layer of the hydra - the ectoderm. Most of all here are skin-muscular. By touching their sides, these cells create the cover of the hydra. At the base of each such cell there is a contractile muscle fiber, which plays an important role in the movement of the animal. When everyone's fiber skin-muscular cells contract, the hydra's body contracts. If the fibers contract on only one side of the body, then the hydra bends in that direction. Thanks to the work of muscle fibers, the hydra can slowly move from place to place, alternately “stepping” with its sole and tentacles. This movement can be compared to a slow somersault over your head.
The outer layer contains and nerve cells. They have a star-shaped shape, as they are equipped with long processes.
The processes of neighboring nerve cells come into contact with each other and form nerve plexus, covering the entire body of the hydra. Some of the processes approach the skin-muscle cells.
Hydra irritability and reflexes
Hydra is able to sense touch, temperature changes, the appearance of various dissolved substances in water and other irritations. This causes her nerve cells to become excited. If you touch the hydra with a thin needle, then the excitement from irritation of one of the nerve cells is transmitted along the processes to other nerve cells, and from them to the skin-muscle cells. This causes muscle fibers to contract, and the hydra shrinks into a ball.
Picture: Hydra's irritability
In this example, we get acquainted with a complex phenomenon in the animal body - reflex. The reflex consists of three successive stages: perception of irritation, transfer of excitation from this irritation along the nerve cells and response body by any action. Due to the simplicity of the hydra's organization, its reflexes are very uniform. In the future we will become familiar with much more complex reflexes in more highly organized animals.
Hydra stinging cells
Pattern: Stringing or nettle cells of Hydra
The entire body of the hydra and especially its tentacles are seated with a large number stinging, or nettles cells. Each of these cells has a complex structure. In addition to the cytoplasm and nucleus, it contains a bubble-like stinging capsule, inside which a thin tube is folded - stinging thread. Sticking out of the cage sensitive hair. As soon as a crustacean, small fish or other small animal touches a sensitive hair, the stinging thread quickly straightens, its end is thrown out and pierces the victim. Through a channel passing inside the thread, poison enters the body of the prey from the stinging capsule, causing the death of small animals. As a rule, many stinging cells are fired at once. Then the hydra uses its tentacles to pull the prey to its mouth and swallows it. The stinging cells also serve the hydra for protection. Fish and aquatic insects do not eat hydras, which burn their enemies. The poison from the capsules is reminiscent of nettle poison in its effect on the body of large animals.
The inner layer of cells is the hydra endoderm
Figure: structure of the inner layer of cells - hydra endoderm
Inner layer of cells - endoderm A. The cells of the inner layer - the endoderm - have contractile muscle fibers, but the main role of these cells is to digest food. They secrete digestive juice into the intestinal cavity, under the influence of which the hydra’s prey softens and breaks down into small particles. Some of the cells of the inner layer are equipped with several long flagella (as in flagellated protozoa). The flagella are in constant motion and sweep particles towards the cells. The cells of the inner layer are capable of releasing pseudopods (like those of an amoeba) and capturing food with them. Further digestion occurs inside the cell, in vacuoles (like in protozoa). Undigested food remains are thrown out through the mouth.
The hydra has no special respiratory organs; oxygen dissolved in water penetrates the hydra through the entire surface of its body.
Hydra regeneration
The outer layer of the hydra's body also contains very small round cells with large nuclei. These cells are called intermediate. They play a very important role in the life of the hydra. With any damage to the body, intermediate cells located near the wounds begin to grow rapidly. From them, skin-muscle, nerve and other cells are formed, and the wounded area quickly heals.
If you cut a hydra crosswise, tentacles grow on one of its halves and a mouth appears, and a stalk appears on the other. You get two hydras.
The process of restoring lost or damaged body parts is called regeneration. Hydra has a highly developed ability to regenerate.
Regeneration, to one degree or another, is also characteristic of other animals and humans. Thus, in earthworms it is possible to regenerate a whole organism from their parts; in amphibians (frogs, newts) entire limbs, various parts of the eye, tail and internal organs can be restored. When a person is cut, the skin is restored.
Hydra reproduction
Asexual reproduction of hydra by budding
Figure: Hydra asexual reproduction by budding
Hydra reproduces asexually and sexually. In summer, a small tubercle appears on the hydra’s body - a protrusion of the wall of its body. This tubercle grows and stretches out. Tentacles appear at its end, and a mouth breaks out between them. This is how the young hydra develops, which at first remains connected to the mother with the help of a stalk. Outwardly, all this resembles the development of a plant shoot from a bud (hence the name of this phenomenon - budding). When the little hydra grows up, it separates from the mother’s body and begins to live independently.
Hydra sexual reproduction
By autumn, with the onset of unfavorable conditions, hydras die, but before that, sex cells develop in their body. There are two types of germ cells: ovoid, or female, and spermatozoa, or male reproductive cells. Sperm are similar to flagellated protozoa. They leave the hydra's body and swim using a long flagellum.
Figure: Hydra sexual reproduction
The hydra egg cell is similar to an amoeba and has pseudopods. The sperm swims up to the hydra with the egg cell and penetrates inside it, and the nuclei of both sex cells merge. Happening fertilization. After this, the pseudopods are retracted, the cell is rounded, and a thick shell is formed on its surface - a egg. At the end of autumn, the hydra dies, but the egg remains alive and falls to the bottom. In the spring, the fertilized egg begins to divide, the resulting cells are arranged in two layers. From them a small hydra develops, which, with the onset of warm weather, comes out through a break in the egg shell.
Thus, the multicellular animal hydra at the beginning of its life consists of one cell - an egg.
Theoretical round of the school stage of the All-Russian Biology Olympiad,
Class
Task completion time 120 minutes
Maximum score: 55 points
Part I You are offered test tasks that require a choice only one answer
out of four possible. The maximum number of points you can score is 20
(1 point for each test task).
1. Systematics is a science that studies:
a) diversity and distribution of organisms into groups
b) features of the metabolism of organisms
c) external and internal structure of organisms
d) behavior of living organisms.
2. Plants as opposed to animals:
a) grow up to a certain age
b) use organic substances formed in their body from inorganic
c) able to move actively
d) feed on ready-made organic substances.
3. All living cells:
a) breathe, grow
b) feed, reproduce
c) breathe, eat, develop, reproduce
d) breathe, eat, photosynthesize, grow, develop.
a) aspen leaf
b) cells of the stomach walls
c) an oak tree growing from an acorn
d) birch forest
5. There is no cytoplasm in the cells:
a) nettle
b) boletus
c) cholera vibrio
d) the virus that causes rabies
6. The main organs of a flowering plant:
a) root, stem, leaves, buds
b) root, stem, buds, flower
c) root, shoot, flower, fruit with seeds
d) root, stem, flower.
7. Cells of the root cap -
a) continuously divide
b) conduct water and minerals
c) absorb water and minerals
d) protect the root tip from damage.
8. Only a bacterial cell is characterized by:
a) cell wall containing murein
b) cell wall containing cellulose
c) plasma membrane without a cell wall
d) plasma membrane and mucous capsule.
9. Cyanobacteria synthesize:
a) organic substances from inorganic ones
b) vitamins
c) mineral compounds
d) cyanide compounds.
10. Autotrophic bacteria do NOT include:
a) iron bacteria
b) botulism bacterium
c) sulfur bacteria
d) hydrogen bacterium
11. The similarity between fly agaric and fern is manifested in the fact that they:
a) heterotrophs
b) store glycogen
c) have unlimited growth
d) there is mycelium.
12. The same function is typical for:
a) spores of bacteria and fungi
b) bacterial spores and protozoan cysts
c) spores of bacteria and plant seeds
d) there is no correct answer
13. The global role of fungi and bacteria is that:
a) they are food for many animals
b) they are medicine for many animals
c) they produce oxygen for animals to breathe
d) they are destroyers of organic matter
14. The vegetative body of the tinder fungus is formed:
a) hyphae
b) mycelium
c) mycelium
d) everything is correct.
15. There is no stage in the life cycle of sphagnum:
a) gametophyte
b) outgrowth
c) sporophyte
d) everything is correct.
16. Malaria is caused by:
a) amoeba
b) trypanosomes
c) plasmodia
d) ciliates.
17. Where do hydra get new stinging cells from:
a) stinging cells divide
b) are formed from intermediate cells
c) are formed from integumentary muscle cells
d) they are not restored; when their supply runs out, the hydra dies.
18. Roundworms differ from flatworms by the presence of:
a) nervous system; b
b) excretory system
c) cuticles;
d) anus.
19. The intestines are absent in:
a) wide tapeworm
b) liver fluke
c) pinworms;
d) roundworms
20. Insects with complete metamorphosis include:
a) Orthoptera, Diptera
b) hemiptera, homoptera
c) Coleoptera, Lepidoptera
d) Hymenoptera, dragonflies.
Task 2. Test tasks with one answer option out of four
A characteristic feature of coelenterates is the presence of stinging cells in the integument (Fig. 93). They develop from intermediate cells and contain a special oval stinging capsule with dense walls. The capsule is filled with liquid, and at one end of the capsule its wall is pushed inward in the form of a very thin but hollow process, which twists into the capsule into a spirally curled stinging thread. The stinging cells serve the hydra as a weapon of attack and defense.
On the outer surface of the cell there is a thin sensitive hair - cnidocil. Studying stinging cells using an electron microscope showed significant complexity in the structure of the cnidocil (Fig. 93). It consists of a long flagellum surrounded by 18-22 thin finger-like outgrowths of the cytoplasm - microvilli. In structure, the cnidocil flagellum is very similar to the flagella and cilia of protozoa, but unlike them, it is motionless. When prey or an enemy touches the flagellum, the latter deflects and touches one or more microvilli, which leads to the excitation of the stinging cell. At the same time, the stinging capsule throws out an elastic thread that turns outward and straightens out like an arrow. The thread, like a harpoon, is seated with back-facing spines, and at the base it bears larger spines. Thread pricks are poisonous and can paralyze small animals. After the thread is thrown out, the stinging cell dies.
Hydra has several categories of capsules, the functions of which are different. The large capsules considered, which serve to pierce the covers and damage prey, are called penetrants (Fig. 93). Much smaller ones - volvents - have short spirally twisted threads that wrap around various protrusions (setae, hairs, etc.) on the body of the prey and in this way hold it. Finally, elongated stinging capsules - glutinants - are glued to the body of the prey with long sticky threads.
In this article we will continue to consider the world of living organisms of the animal kingdom.
The phylum is one of the first most simply organized multicellular animals (there is an even more primitive type - the Sponge type, which is not currently considered in the school curriculum).
Yes, of the multicellular life forms, coelenterates are one of the most primitive, but you must agree, what enormous progress life has made ! A real breakthrough was made - the transition from, that is, unicellular life form to multicellular.
In addition, coelenterates are TWO-layer . They have an outer layer of cells - ECTODermis and an inner layer of cells - ENTODermis. Between these layers of cells is the noncellular mesoglea (8) - not to be confused with, which evolutionarily will appear only in the next type of animal - FLATWORMS.
Moreover, in both layers the cells are heterogeneous, differentiated, and specialized to perform certain functions.
As we can see from the figure, there are 5 types of different cells in the ectoderm
Of particular interest may be the intermediate cells of the ectoderm (5), which are capable of forming any type of cell. Thus, the term “” of higher animals can to some extent be compared with the “intermediate cells” of coelenterates.
Availability internal cavity (not to be confused with the term "body cavity"), which can be called “gut” or “stomach”, provides double digestion to coelenterates : and inside the “gut” due to enzymes secreted by glandular cells (7) of the endoderm (narrower and darker in color in the diagram), and intracellular due to digestive muscle cells (6) - large cells with flagella.
Feeding: predators, actively capture prey with tentacles, using stinging cells, paralyzing prey. Digestion how gastric(“intracavitary”) due to enzymes secreted by glandular cells, and intracellular- digestive muscle cells.
Breathing and elimination products of exchange : the entire surface of the body.
Irritability: primitive diffuse nervous system. Attached forms have only touch from their sensory organs, while free-swimming forms have them in their tentacles organs of vision(eyes - distinguish light from darkness) and balance organs — statocysts.
Regeneration: possible through reproduction and differentiation intermediate cells.
Reproduction : R dioecious, there is also hermaphrodites- ovaries and testes develop on one individual.
Sexual reproduction - direct or with metamorphosis (larva planula ).
Asexual reproduction - budding the formation of an outgrowth on the mother’s body and strobilation (multiple transverse divisions of the polyp).
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For the first time in coelenterates there appears and nervous system, so-called diffuse or star-shaped. These are specialized cells, “scattered” in the lower part of the ectoderm and connected to each other by long processes.
For the first time in coelenterates, a real sexual process. I write “real” because the primitive sexual process—conjugation—is present in bacteria and some protozoa (ciliates, for example). In coelenterates, in specialized areas of the body, some of the cells divide, forming male and female haploid cells - gametes. So hydra can reproduce both asexually by budding (analogue of vegetative propagation of plants) and sexually.
Jellyfish, in general, are characterized by the development of sexual and asexual life forms.
So, here are the main ones that life underwent during the transition from unicellular protozoa to the first multicellular coelenterates :
1. Multicellular life form.
2. Differentiation of cells has occurred, their specialization according to the functions they perform.
3. Body made of a double layer of cells - ectoderm and endoderm.
4. The appearance of the real sexual process.
5. The appearance of internal digestion.
6. The appearance of a diffuse type nervous system.
He described the coelenterates in such a way that one can think anything - life was so “spent” in its sophisticated ingenuity creating them that it is not clear what kind of progress can still be expected? But all kinds of “beauties” await us ahead worms, an even more advanced form of life!
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Anyone who has questions about the article for a biology tutor via Skype, comments, or suggestions - please leave a comment.
Hydra is a typical representative of the class Hydrozoa. It has a cylindrical body shape, reaching a length of up to 1-2 cm. At one pole there is a mouth surrounded by tentacles, the number of which in different species varies from 6 to 12. At the opposite pole, hydras have a sole, which serves to attach the animal to the substrate.
Sense organs
In the ectoderm of hydras there are stinging or nettle cells that serve for defense or attack. In the inner part of the cell there is a capsule with a spirally twisted thread.
Outside this cell there is a sensitive hair. If any small animal touches a hair, the stinging thread quickly shoots out and pierces the victim, who dies from the poison that gets along the thread. Usually many stinging cells are released at the same time. Fish and other animals do not eat hydras.
The tentacles serve not only for touch, but also for capturing food - various small aquatic animals.
Hydras have epithelial-muscle cells in the ectoderm and endoderm. Thanks to the contraction of the muscle fibers of these cells, the hydra moves, “stepping” alternately with its tentacles and its sole.
Nervous system
The nerve cells that form a network throughout the body are located in the mesoglea, and the processes of the cells extend outwards and into the body of the hydra. This type of structure of the nervous system is called diffuse. Especially many nerve cells are located in the hydra around the mouth, on the tentacles and sole. Thus, coelenterates already have the simplest coordination of functions.
Hydrozoans are irritable. When nerve cells are irritated by various stimuli (mechanical, chemical, etc.), the perceived irritation spreads throughout all cells. Thanks to the contraction of muscle fibers, the hydra's body can shrink into a ball.
Thus, for the first time in the organic world, reflexes appear in coelenterates. In animals of this type, reflexes are still monotonous. In more organized animals they become more complex during the process of evolution.
Digestive system
All hydras are predators. Having captured, paralyzed and killed prey with the help of stinging cells, the hydra with its tentacles pulls it towards the mouth opening, which can stretch very much. Next, food enters the gastric cavity, lined with glandular and epithelial-muscular endoderm cells.
Digestive juice is produced by glandular cells. It contains proteolytic enzymes that promote the absorption of proteins. Food in the gastric cavity is digested by digestive juices and breaks down into small particles. The endoderm cells have 2-5 flagella that mix food in the gastric cavity.
Pseudopodia of epithelial muscle cells capture food particles and subsequently intracellular digestion occurs. Undigested food remains are removed through the mouth. Thus, in hydroids, for the first time, cavity, or extracellular, digestion appears, running in parallel with the more primitive intracellular digestion.
Organ regeneration
In the ectoderm of the hydra there are intermediate cells, from which, when the body is damaged, nerve, epithelial-muscular and other cells are formed. This promotes rapid healing of the wounded area and regeneration.
If a hydra's tentacle is cut off, it will recover. Moreover, if the hydra is cut into several parts (even up to 200), each of them will restore the entire organism. Using the example of hydra and other animals, scientists study the phenomenon of regeneration. The identified patterns are necessary for the development of methods for treating wounds in humans and many vertebrate species.
Hydra reproduction methods
All hydrozoans reproduce in two ways - asexual and sexual. Asexual reproduction is as follows. In the summer, approximately halfway through, the ectoderm and endoderm protrude from the hydra's body. A mound or bud is formed. Due to cell proliferation, the size of the kidney increases.
The gastric cavity of the daughter hydra communicates with the cavity of the mother. A new mouth and tentacles form at the free end of the bud. At the base, the bud is laced, the young hydra is separated from the mother and begins to lead an independent existence.
Sexual reproduction in hydrozoans under natural conditions is observed in autumn. Some species of hydra are dioecious, while others are hermaphroditic. In freshwater hydra, female and male sex glands, or gonads, are formed from intermediate ectoderm cells, that is, these animals are hermaphrodites. The testes develop closer to the mouth of the hydra, and the ovaries develop closer to the sole. If many motile spermatozoons are formed in the testes, then only one egg matures in the ovaries.
Hermaphroditic individuals
In all hermaphroditic forms of hydrozoans, spermatozoons mature earlier than eggs. Therefore, fertilization occurs cross-fertilization, and therefore self-fertilization cannot occur. Fertilization of eggs occurs in the mother in the autumn. After fertilization, hydras, as a rule, die, and the eggs remain in a dormant state until spring, when new young hydras develop from them.
Budding
Marine hydroid polyps can be, like hydra, solitary, but more often they live in colonies that appear due to the budding of a large number of polyps. Polyp colonies often consist of a huge number of individuals.
In marine hydroid polyps, in addition to asexual individuals, during reproduction through budding, sexual individuals, or jellyfish, are formed.