The structure and functions of the internal organs of amphibians lesson. “Structure and activity of the internal organ systems of amphibians” lesson plan in biology (grade 7) on the topic

Class amphibians or amphibians

general characteristics

Amphibians or amphibians (lat. Amphibia) - a class of vertebrate four-legged animals, including, among others, newts, salamanders, frogs and caecilians - about 4500 in total modern species, which makes this class relatively small.

The group of amphibians belongs to the most primitive terrestrial vertebrates, occupying an intermediate position between terrestrial and aquatic vertebrates: reproduction and development occurs in aquatic environment, and adults live on land.

Skin

All amphibians have smooth, thin skin that is relatively easily permeable to liquids and gases. The structure of the skin is characteristic of vertebrates: a multilayered epidermis and the skin itself (corium) are distinguished. The skin is rich in cutaneous glands that secrete mucus. For some, mucus may be toxic or facilitate gas exchange. The skin is an additional organ of gas exchange and is equipped with a dense network of capillaries.

Horny formations are very rare, and ossifications of the skin are also rare: Ephippiger aurantiacus and the horned toad of the species Ceratophrys dorsata have a bony plate in the skin of the back, legless amphibians have scales; Toads sometimes develop lime deposits in their skin when they get old.

Skeleton

The body is divided into a head, torso, tail (in caudates) and five-fingered limbs. The head is movable and connected to the body. The skeleton is divided into sections:

axial skeleton (spine);

head skeleton (skull);

skeleton of paired limbs.

The spine is divided into 4 sections: cervical, trunk, sacral and caudal. The number of vertebrae ranges from 10 in tailless amphibians to 200 in legless amphibians.

The cervical vertebra is movably attached to the occipital part of the skull (provides head mobility). Ribs are attached to the trunk vertebrae (except in tailless animals, which lack them). The only sacral vertebra is connected to the pelvic girdle. In tailless animals, the vertebrae of the caudal region are fused into one bone.

The flat and wide skull articulates with the spine using 2 condyles formed by the occipital bones.

The skeleton of the limbs is formed by the skeleton of the limb girdle and the skeleton of the free limbs. The shoulder girdle lies in the thickness of the muscles and includes paired shoulder blades, collarbones and crow bones connected to the sternum. The skeleton of the forelimb consists of the shoulder (humerus), forearm (radius and ulna) and hand (bones of the wrist, metacarpus and phalanges). The pelvic girdle consists of paired iliac ischial and pubic bones fused together. It is attached to the sacral vertebra through the ilia. The skeleton of the hind limb includes the thigh, tibia (tibia and fibula) and foot. Bones of the tarsus, metatarsus and phalanges of the fingers. In anurans, the bones of the forearm and tibia are fused. All bones of the hind limb are greatly elongated, forming powerful levers for mobile jumping.

Musculature

Musculature is divided into the muscles of the trunk and limbs. The trunk muscles are segmented. Special muscle groups provide complex movements lever limbs. The levator and depressor muscles are located on the head.

In a frog, for example, the muscles are best developed in the jaw area and the muscles of the limbs. In Tailed Amphibians ( fire salamander) the tail muscles are also strongly developed

Respiratory system

The respiratory organ of amphibians is:

lungs (special air breathing organs);

skin and mucous lining of the oropharyngeal cavity (additional respiratory organs);

gills (in some aquatic inhabitants and in tadpoles).

Most species (except for lungless salamanders) have small lungs, in the form of thin-walled sacs entwined with a dense network of blood vessels. Each lung opens with an independent opening into the laryngeal-tracheal cavity (here are located vocal cords opening with a slit into the oropharyngeal cavity). Air is forced into the lungs by changing the volume of the oropharyngeal cavity: air enters the oropharyngeal cavity through the nostrils when its bottom is lowered. When the bottom rises, air is pushed into the lungs. In toads, adapted to living in more arid environments, the skin becomes keratinized, and respiration occurs primarily through the lungs.

Circulatory organs

The circulatory system is closed, the heart is three-chambered with mixing of blood in the ventricle (except for lungless salamanders, which have a two-chambered heart). Body temperature depends on temperature environment.

The circulatory system consists of the systemic and pulmonary circulations. The appearance of the second circle is associated with the acquisition of pulmonary breathing. The heart consists of two atria (in the right atrium the blood is mixed, mainly venous, and in the left - arterial) and one ventricle. Inside the walls of the ventricle, folds form that prevent the mixing of arterial and venous blood. An arterial cone, equipped with a spiral valve, emerges from the ventricle.

Arteries:

cutaneous pulmonary arteries (carry venous blood to the lungs and skin)

carotid arteries (the organs of the head are supplied with arterial blood)

The aortic arches carry mixed blood to the rest of the body.

The small circle is pulmonary, begins with the cutaneous pulmonary arteries, carrying blood to the respiratory organs (lungs and skin); From the lungs, oxygenated blood is collected in paired pulmonary veins, which flow into the left atrium.

The systemic circulation begins with the aortic arches and carotid arteries, which branch into organs and tissues. Venous blood enters the right atrium through the paired anterior vena cava and the unpaired posterior vena cava. In addition, oxidized blood from the skin enters the anterior vena cava and therefore the blood in the right atrium is mixed.

Due to the fact that the body's organs are supplied with mixed blood, amphibians have a low metabolic rate and therefore are cold-blooded animals.

Digestive organs

All amphibians feed only on mobile prey. The tongue is located at the bottom of the oropharyngeal cavity. In tailless animals, its front end is attached to the lower jaws; when catching insects, the tongue is thrown out of the mouth, and the prey is attached to it. The jaws have teeth that serve only to hold prey. In frogs they are located only on the upper jaw.

Ducts open into the oropharyngeal cavity salivary glands, the secretion of which does not contain digestive enzymes. From the oropharyngeal cavity, food enters the stomach through the esophagus, and from there into the duodenum. The ducts of the liver and pancreas open here. Digestion of food occurs in the stomach and duodenum Small intestine passes into the colon, ending with the rectum, which forms an extension - the cloaca.

Excretory organs

The excretory organs are paired trunk kidneys, from which ureters depart, opening into the cloaca. In the wall of the cloaca there is an opening of the bladder into which urine that enters the cloaca from the ureters flows. There is no reabsorption of water in the trunk kidneys. After filling the bladder and contracting the muscles of its walls, concentrated urine is discharged into the cloaca and thrown out. Part of the products of exchange and a large number of moisture is released through the skin.

These features did not allow amphibians to completely transition to a terrestrial lifestyle.

Nervous system

Compared to fish, the brain weight of amphibians is greater. The weight of the brain as a percentage of body weight is in modern cartilaginous fish 0.06-0.44%, in bony fishes 0.02-0.94, in tailed amphibians 0.29-0.36, in tailless amphibians 0.50-0.73%

The brain consists of 5 sections:

the forebrain is relatively large; divided into 2 hemispheres; has large olfactory lobes;

the diencephalon is well developed;

the cerebellum is poorly developed;

the medulla oblongata is the center of the respiratory, circulatory and digestive system;

midbrain relatively small.

Sense organs

The eyes are similar to the eyes of fish, but do not have silvery and reflective membranes, as well as a sickle-shaped process. Only Proteas have underdeveloped eyes. There are adaptations for operation in the air. Higher amphibians have upper (leathery) and lower (transparent) movable eyelids. The nictitating membrane (instead of the lower eyelid in most anurans) performs a protective function. There are no lacrimal glands, but there is a Harderian gland, the secretion of which moistens the cornea and protects it from drying out. The cornea is convex. The lens has the shape of a biconvex lens, the diameter of which varies depending on the lighting; accommodation occurs due to changes in the distance of the lens to the retina. Many have developed color vision.

The olfactory organs function only in the air and are represented by paired olfactory sacs. Their walls are lined with olfactory epithelium. They open outward with the nostrils, and into the oropharyngeal cavity with the choanae.

There is a new section in the organ of hearing - the middle ear. The external auditory opening is closed by the eardrum, connected to the auditory ossicle - the stapes. The stirrup rests on the oval window, which leads into the cavity of the inner ear, transmitting vibrations of the eardrum to it. To equalize the pressure on both sides of the eardrum, the middle ear cavity is connected to the oropharyngeal cavity by the auditory tube.

The organ of touch is the skin, which contains tactile nerve endings. Aquatic representatives and tadpoles have lateral line organs.

Genitals

All amphibians are dioecious. In most amphibians, fertilization occurs externally (in water).

During the breeding season, the ovaries filled with mature eggs fill almost the entire abdominal cavity of females. Ripe eggs fall into the abdominal cavity of the body, enter the funnel of the oviduct and, after passing through it, are brought out through the cloaca.

Males have paired testes. The seminiferous tubules extending from them enter the ureters, which at the same time serve as vas deferens for the males. They also open into the cloaca.

Life cycle

IN life cycle Amphibians have four stages of development: egg, larva, metamorphosis, and imago.

Amphibian eggs (eggs), like fish eggs, do not have a waterproof shell. For the egg to develop, it needs constant moisture. The vast majority of amphibians lay eggs in fresh water bodies, but exceptions are known: caecilians, amphium frog, giant salamanders, Alleghamian cryptobranchs and some other amphibians lay eggs on land. Even in these cases, the eggs need high environmental humidity, the provision of which falls on the parent. Species are known that carry eggs on their bodies: the female reticulated copefrog attaches them to her stomach, and the male midwife toads wrap the cord-like clutch around their hind legs. The care of the offspring of the Suriname pipa looks especially unusual - the fertilized eggs are pressed by the male into the back of the female and the latter carries it on herself until young pipas hatch from the eggs.

The eggs hatch into larvae that lead water image life. In their structure, the larvae resemble fish: they lack paired limbs, breathe with gills (external, then internal); have a two-chamber heart and one circle of blood circulation, lateral line organs.

Undergoing metamorphosis, the larvae turn into adults leading a terrestrial lifestyle. The process of metamorphosis in tailless amphibians occurs rapidly, while in primitive salamanders and legless amphibians it is greatly extended over time.

Amphibians of some species take care of their offspring (toads, tree frogs).

Lifestyle

Most amphibians live in damp places, alternating between land and water, but there are some purely aquatic species, as well as species that live exclusively in trees. The insufficient adaptability of amphibians to live in the terrestrial environment causes sudden changes in their lifestyle due to seasonal changes in living conditions. Amphibians are capable of hibernating for long periods of time unfavorable conditions(cold, drought, etc.). In some species, activity may change from nocturnal to diurnal as temperatures drop at night. Amphibians are active only in warm conditions. At a temperature of +7 - +8°C, most species fall into torpor, and at −2°C they die. But some amphibians are able to withstand prolonged freezing, drying out, and also regenerate significant lost parts of the body.

Amphibians cannot live in salt water, which is due to the hypotonicity of tissue solutions to sea ​​water, as well as high skin permeability. Therefore, they are absent from most oceanic islands, where conditions are generally favorable for them.

Nutrition

All modern amphibians in the imago stage are predators, feed on small animals (mainly insects and invertebrates), and are prone to cannibalism. There are no herbivores among amphibians due to their extremely sluggish metabolism. Into the diet aquatic species may include juvenile fish, and the largest ones may prey on chicks of waterfowl and small rodents caught in the water.

The feeding pattern of the larvae of tailed amphibians is almost similar to the feeding of adult animals. The larvae of anurans are fundamentally different, feeding on plant food and detritus (a set of small (from several microns to several cm) undecomposed particles of plant and animal organisms or their excretions), switching to predation only at the end of the larval stage.

Reproduction

Common feature reproduction of almost all amphibians is their attachment during this period to water, where they lay eggs and where the development of larvae occurs.

Amphibian poison

The most poisonous vertebrates on Earth belong to the order of amphibians - dart frogs. The poison, which is secreted by the skin glands of amphibians, contains substances that kill bacteria (bactericides). Most amphibians in Russia have poison that is completely harmless to humans. However, many tropical frogs are not so safe. The absolute “champion” in terms of toxicity among all creatures, including snakes, should be recognized as the resident tropical forests Colombia - a tiny, only 2-3 cm in size, cocoa frog. Her skin mucus is terribly poisonous (contains batrachotoxin). Indians use the skin of cocoa to make poison for arrows. One frog is enough to poison 50 arrows. 2 mg of purified poison from another South American frog, the terrible frog, is enough to kill a person. Despite terrible weapon, this frog has a mortal enemy - the small snake Leimadophis epinephelus, which feasts on young leaf climbers.

Amphibians and humans

Due to their vitality, amphibians are often used as laboratory animals.

Known healing properties amphibian poison. Powder from dried toad skins is used in China and Japan for dropsy, to improve heart function, for toothache and for bleeding gums. Relatively recently in tropical forests South America was found tree frog, releasing substances that are 200 times more effective than morphine.

Classification

Modern representatives are represented by three groups:

Anurans (frogs, toads, tree frogs, etc.) - about 2100 species.

Tailed animals (salamanders, newts, etc.) - about 280 species.

Legless, the only family of caecilians - about 60 species.

Evolution

In evolutionary terms, amphibians descended from ancient lobe-finned fish and gave rise to representatives of the class reptiles. The most primitive order of amphibians are the tailed ones. Tailed amphibians are most similar to the most ancient representatives class. More specialized groups are the tailless amphibians and the legless amphibians.

There is still debate about the origin of amphibians, and according to the latest data, amphibians descend from ancient lobe-finned fish, specifically from the order Rhipidistia. In terms of the structure of the limbs and skull, these fish are close to fossil amphibians (stegocephalians), which are considered the ancestors of modern amphibians. The most archaic group is considered to be ichthyostegids, which retain a number of features characteristic of fish - a caudal fin, rudiments of gill covers, organs corresponding to the organs of the lateral line of fish.

Class amphibians- these are cold-blooded animals associated with both water and terrestrial environment; there are about 5000 species. They are also called amphibians.

The structure of the amphibian class

Amphibian organ	What parts does it consist of?
SKELETON
Head skeleton	Skull box; Jaws - upper and lower	Brain protection Capturing food
Spine	Vertebrae (there is a cervical vertebra); tail bone	Body support, protection internal organs
Forelimb belt	Sternum, two crow bones, two collarbones and two shoulder blades	Connects the limbs with the spine
Hind limb belt	Fused pelvic bones attached to the spine	Hind leg support
Forelimb	Humerus, two fused bones of the forearm, small bones of the hand, bones of the four fingers	Support while moving
Hind limb	Femur, two fused bones of the lower leg, bones of the foot and five toes	Push-off while moving
NERVOUS SYSTEM
Brain	Divisions: anterior (better developed than in fish), middle, intermediate, oblongata, cerebellum (due to the uniformity of motor reactions, less developed than in fish)	Movement control, unconditioned and conditioned reflexes
Spinal cord		implementation of simple reflexes, conduction of nerve impulses
	perception and conduction of signals
Sense organs	The organ of vision is the eyes, protected by eyelids; The organ of hearing is the ear (consists of the middle and inner ear, the organs of smell and balance are located in the brain	Perception of signals from the external environment
ORGANS OF THE BODY CAVITY
Digestive system	1. Digestive tract (mouth, pharynx, esophagus, stomach, intestines, anus) 2. Digestive glands (pancreas, liver)	1. Capturing, chopping, moving food 2. secretion of juices that promote food digestion
Respiratory system(may be pulmonary and cutaneous respiration)	Lungs (sacs with elastic walls in which many capillaries branch)	Gas exchange
Circulatory system	Three-chambered heart (two atria and one ventricle), arteries, veins, capillaries; two circles of blood circulation	Supplying all body cells with oxygen and nutrients, removal of decomposition products

Origin of the class Amphibians

Amphibians or amphibians appeared about 375 million years ago. The first amphibians descended from ancient lobe-finned fish, which were of enormous size, which in turn also reached gigantic sizes.

Classification of Amphibians

Amphibians are divided into 3 main orders:

	Representatives	Features and numbers
Squad Tailed	representatives are newts, salamanders, ambistoms, sirens	All of them have an elongated body, which turns into a tail, and the limbs are short and weak. A feature of tailed animals is the high regeneration of body parts, which happens when animals restore up to the half of their body. This order includes approximately 500 species of amphibians.
Tailless Squad	toads, frogs, toads, tree frogs and others	Representatives of this order have well-developed hind limbs for jumping movement and lack a tail. Includes approximately 4,000 species of amphibians
Legless Squad	these include worms	Primitive amphibians, which have neither tails nor limbs, resemble earthworms.

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A source of information: Biology in tables and diagrams./ Edition 2, - St. Petersburg: 2004.

Let us consider the systems of internal organs of amphibians also using the example of the lake frog (Fig. 98). The digestive system of amphibians is more complex than the digestive system of fish. It begins with the oral cavity, at the bottom

To which the tongue is attached at the front end. (Consider how the way a frog's tongue is attached differs from the way a human's tongue is attached.) The main function of the tongue is to catch insects, not to push food through. The ducts of the salivary glands open into the oral cavity, producing saliva intended for moistening food. (Remember that other animals have salivary glands and what is their purpose.) The oral cavity passes into the esophagus, which opens into the stomach, where food digestion begins. The duodenum lies under the stomach and receives the bile duct of the liver and the pancreatic duct. The intestine forms several loops, passes into the rectum and ends in the cloaca. Water is absorbed in the intestines.

Oddly enough, some amphibians are helped to swallow food... by their eyes. Perhaps you have watched a frog roll its eyes in pain as it eats a fly. This is by no means a sign of sympathy for the victim, but the process of swallowing food.

The excretory system of amphibians is similar excretory system fish The bare skin of the lake frog does not prevent water from penetrating into the body, so excess water constantly accumulates in it. This excess water is removed by large body buds (fish also have similar ones). From the kidneys, urine is discharged through the ureters into the cloaca.

Amphibians living in the desert know how to save water. That is why urine is not produced in the South American quakia - phylomedusa. Harmful substances in it accumulate in the bladder in the form of solid crystals and dissolve when the animal enters the water.

Respiratory system. The frog's respiratory organs - the lungs - look like bags divided into cells. The lungs are penetrated by a branched network of blood vessels.

The inhalation mechanism is as follows: when the bottom of the oropharyngeal cavity drops, a rarefied space is created in it, and air enters through the open nostrils. Next, the nostrils are closed with special valves, and the bottom of the cavity rises, pushing air into the lungs.

Due to insufficient development of the lungs in amphibians great importance acquires skin respiration. The amount of oxygen entering the body through the skin, and carbon dioxide also released through the skin, is half the total volume of gases necessary for the animal to breathe.

A pond frog, which was placed in water and thus deprived of the ability to breathe with its lungs, can live for three weeks, a grass frog - for a month. An ordinary newt once stayed underwater for seven months! He felt great and would have sat there for who knows how long, but the scientists were tired of watching him. The whole family amphibians - bezlegenev salamanders - do without lungs at all, and breathe only through the skin and using the surface of the oral cavity.

The circulatory system of amphibians is adapted to the pulmonary type of breathing. (Remember the structure of the perch’s heart.) This means that the lake frog has a three-chambered heart, consisting of two atria and a ventricle, and two circles of blood circulation allow partial separation of arterial and venous blood and better saturation of body tissues with oxygen. Mixed blood collects in the right atrium: venous, saturated carbon dioxide, - from internal organs, and arterial, oxygen-rich - from the skin. Only arterial blood enters the left atrium and is enriched with oxygen in the lungs. Both atria contract simultaneously, and blood from them enters the ventricle. The blood in the ventricle is mixed. Thanks to the presence of the heart valve, blood is distributed: arterial blood goes to the brain, venous blood goes to the lungs and skin, where it is saturated with oxygen and turns into arterial blood, and mixed blood goes to all organs. Due to the fact that in amphibians the arterial and venous blood mixes and the saturation of tissues with oxygen does not occur quickly enough, the metabolism is slowed down. (Remember what metabolism is.) Therefore, the body temperature of amphibians, like fish, does not differ from the ambient temperature.

The nervous system of the lake frog is more complex than the nervous system of fish. The frog's more developed forebrain is divided into two cerebral hemispheres, thanks to which the frog is a smarter creature than, for example, a perch.

Sense organs. Complications of the nervous system are directly related to the development of the sensory organs.

The frog's visual organs - the eyes - are well adapted to terrestrial conditions. She is able to see moving objects at a considerable distance, and also follow prey without turning her head and body.

The frog's hearing organs consist not only of the internal (like in fish), but also of the middle ear. The outer opening of the middle ear cavity is covered with the eardrum - a special elastic membrane. The middle ear includes the auditory ossicle - the stapes, which transmits signals from the eardrum to the inner ear.

The olfactory organs are represented by paired external and internal nostrils and are quite well developed. With their help, amphibians find their way to their native reservoir, covering a distance of more than a kilometer.

The organ of taste is the taste buds, which are located on the tongue. You can observe how the frog first grabs an inedible object with its tongue, and then gets rid of it by pushing it out of its mouth with its front paw.

Unlike fish, amphibians more complex structure nervous, digestive and circulatory systems, are lungs, and sense organs are better developed. However, the structure of the excretory system is similar to the excretory system of fish.

Terms and concepts: duodenum, bile duct, pancreas, rectum, oropharyngeal cavity, cutaneous respiration, cerebral hemispheres, middle ear, stirrup.

Check yourself. 1 . What is the structure of the lake frog's digestive system? 2. How does a frog breathe?

3. Why does a frog have pulmonary respiration and not suffocate under water?

4 . How circulatory system The frog's circulatory system is different from that of the fish, what is the difference? 5 . What blood goes to the left atrium and what blood goes to the right? 6. How is the perfection of the nervous system and sensory organs of amphibians manifested in comparison with the nervous system and sensory organs of fish?

How do you think? Why is the presence of two circulation circles and a three-chambered heart a progressive sign of the structure of the animal?

Lesson type: combined.

Pedagogical technology: problem-based learning technology.

Assessment of the pedagogical situation: One of the leading forms of activity for 7th grade students is search activity. Therefore, in lessons for students of this age, the use of such cognitive methods as modeling, analogy, deriving consequences from facts and experiment is justified. These methods are based on the active activity of students. Subject this lesson allows, based on the independent work of students, to determine the content of basic educational units and formulate leading concepts. The search model was chosen as the learning model.

Target: create conditions for students to acquire knowledge about the peculiarities of the organization and operation of the internal organ systems of amphibians.

Tasks:

• continue the formation of a system of ideas about the internal structure of vertebrates using the example of fish and amphibians;
• create conditions for developing the ability to establish cause-and-effect relationships between the structure and functions of organs;
• expand students’ understanding of the possibilities of the modeling method and thought experiment.

Methods: verbal - according to the nature of the predominant means speech activity, and logical - according to the method of obtaining educational information, based on logical operations, visual.

Equipment: media projector, demonstration tables, handouts, presentation.

During the classes

Today's lesson continues the study of chordates. The topic of the lesson is “Structure and operation of the internal organ systems of amphibians”,(start showing the presentation using a media projector)

Lesson objectives:

• remember the internal structure of amphibians using the example of a frog,
• learn to compare the structure of amphibians and fish,
• build a diagram showing the connection of organs in the frog’s body and the dependence of their structure and functions.

Why do you think it is necessary to know the structure of a frog? In what cases can this knowledge be useful in the future in adulthood? ( Suggested answer: for people who choose a profession related to the study of animals). It’s true, and a profession that requires knowledge of the structure and functioning of animal organs is, for example, a doctor, or more precisely a veterinarian.

Remember the children's poem by Korney Chukovsky about such a doctor? ( Suggested answer: Aibolit)

(Watching a video clip based on the cartoon “Aibolit” using a media projector – 2-3 min.)

Of course, in order to treat animals, you need to know how their body works. Can you imagine how much Aibolit probably knew about the structure and functioning of various animal organs! After all, he treated various animals. Remember who? ( Suggested answer: a fox that was bitten by a wasp, a watchdog whose nose was pecked by a chicken, hippos, ostriches, baby sharks, tiger cubs, camels, etc.)

Remember how Aibolit cured a bunny? ( Suggested answer: his legs were sewn on)

Look what wonderful legs Aibolit sewed on the bunny.

(Demonstration of a drawing of a bunny with human legs. Laughter.)

But is something wrong?…( Suggested answer: These are not bunny legs). Of course this is a joke. Doctor Aibolit should know well which legs to sew on and to whom.

But let’s imagine that a frog came to Aibolit for advice on whether it should exchange its heart for a fish’s, two-chambered one, since after all, it lives in water. Today let's try to imagine ourselves in the role of Doctor Aibolit, and give the frog sound advice.

So far we, perhaps, cannot solve the problem of whether to change the frog’s heart or not. And therefore I offer you several opinions. The correct ones may be the key to solving the problem.

Let's try to find them.

1. The main organ in any living organism, on which the work of other organs depends, is the intestine.

2. All organs in the body are connected by blood vessels.

3. Animals living in water do not need oxygen.

4. Blood transports substances.

5. The nervous system of vertebrates is represented by the ventral nerve cord.

6. The movement of blood through the vessels is ensured by the work of the heart.

(Correct judgments: 2, 4, 6)

How can correct judgments be connected with each other?( Suggested answer: you can build the following diagram)

Let's simplify the diagram. Its last part contains elements of one of critical systems organs, which one? ( Suggested answer: circulatory) And are functionally connected with this system ( Suggested answer: all other organ systems)

Correction of the original scheme.

The circulatory system is functionally connected to other organ systems. What are these systems? Let's remember their functions.

Working with a table - a guide

These systems are characteristic of fish and frogs. They perform the same functions in fish and amphibians.

But do you think the structure of these systems will be the same and why? ( Suggested answer: differs due to terrestrial lifestyle)

To understand the structure of the internal organs of a frog, we will use the text. Read the text and enter a “+” sign in one of the columns of the table on your handouts, after first comparing the structure of the organ systems of fish and frogs. Independent work of students using handouts.

Handout 1. Structure and activity of internal organ systems

Digestive system consists of the same organs as those of fish. The wide mouth leads into a large oral cavity. Placed at the bottom real language. It can be thrown out of the mouth and is used for catching small insects. Food moistened with saliva in the mouth passes through the esophagus and is exposed to digestive enzymes in the stomach. Next comes the duodenum (the initial section of the intestine). The ducts of the liver, gall bladder and pancreas open into it. The final digestion of food occurs in the small intestine. Nutrients are absorbed by the intestinal walls and distributed by the blood to all organs and tissues of the body. Undigested residues accumulate in the large intestine. Through the expansion of the cloaca, undigested food remains are removed to the outside.

Handout 2. Respiratory system

frogs breathe lungs and skin. Lungs are small elongated sacs with thin elastic walls. The role of a pump during breathing is performed by the oral cavity, the bottom of which either lowers or rises. Gas exchange occurs in the lungs: oxygen enters the capillaries and is distributed by the blood to all organs and tissues, and carbon dioxide is released from the capillaries into the lungs, which is delivered here by the blood from the organs and tissues. The lungs of amphibians are primitive: they have a small surface area of ​​contact between capillaries and air. Therefore, the skin is important in gas exchange. Gas exchange occurs only through moist skin.

Handout 3. Circulatory system

The heart is three-chambered: two atria and one ventricle. Blood from the internal organs collects in large veins and enters the right atrium. The left atrium receives blood from the lungs and is rich in oxygen. When the atria contract, the blood passes into a single ventricle, where it is partially mixed. Mixed blood enters the aorta and is distributed to all organs and tissues of the body. Thus, amphibians have two circles of blood circulation: a small one, passing through the respiratory organs, and a large one, passing through other organs.

Handout 4. Nervous system

The nervous system consists of central and peripheral sections. The forebrain, divided into two hemispheres, is more developed. The diencephalon is almost hidden from above by the hemispheres. The midbrain associated with vision is moderately developed. The cerebellum is poorly developed. This explains the monotonous movements and sedentary lifestyle.

(Demonstration of the completed summary table through a media projector. Self-test.)

Comparison internal structure fish and amphibians

Organ system	Signs of a frog	Similarities with fish	Difference from fish
Digestive	The alimentary canal is differentiated (divided into sections).	+
	There are salivary glands and a tongue.		+
	The intestine is lengthened due to an additional section.		+
Respiratory	When breathing, oxygen can enter the capillaries from water.	+
	Gas exchange occurs in the lungs and skin.		+
	Gas exchange occurs between atmospheric air and blood.		+
Blood	The circulatory system is closed, there is a heart.	+
	The structure of the heart ensures the division of blood circulation into two circles.		+
	The nervous system includes the spinal cord, brain, and the nerves that arise from them.	+
	The forebrain is divided into two hemispheres.		+
	The cerebellum is poorly developed.		+

We see that the structure of the internal organs of amphibians has changed compared to fish; there are more differences than similarities. With what it can be connected? ( Suggested answer: transition to ground-air environment) Let's return to our diagram. In the diagram we see the functional dependence of the circulatory system and other organ systems. The transition to a land-air environment contributed to changes in all organ systems, and primarily the respiratory system, and therefore the circulatory system also changed - a frog’s heart is not like a fish’s.

Now our knowledge will be enough to model the frog’s body and understand the principle of organization of its heart in connection with the work performed in the body.

(Constructing a diagram on the board from individual elements, connecting them with each other. Accompanied by a story from the teacher.)

The structure of the amphibian heart allows the blood circulation to be functionally divided into two capillary networks. The first capillary network includes the skin and lungs. It saturates the blood with oxygen. The second capillary network includes all other organs. In it, the blood gives up oxygen, turning into venous. The three-chambered heart of a frog, in addition to its suction (pumping) function, performs a distribution function. Blood coming from the lungs (pulmonary circulation) enters the left atrium. Blood from muscles, internal organs and skin (systemic circulation) enters the right atrium. Further separation of blood flows in the heart is achieved physiologically, due to the work of a single ventricle. In the center of the ventricle the blood is partially mixed. When the ventricle contracts, blood is pushed into the arteries through the spiral valve. This valve sequentially opens the entrance first to the vessel going to the lungs and skin, then to the vessel going to other internal organs, and finally to the vessel going to the brain. This feature allows you to “sort” venous blood to the respiratory organs, and arterial blood to the brain.

That. Thanks to the structure and functioning of the heart, the frog has a system for the appropriate distribution of venous and arterial blood between the lungs, internal organs and the brain.

Let us now consider the question of a two-chamber heart. (Students do it independently.) ( Suggested answer: it will work if you remove the septum between the atria. In this case, venous and arterial blood will mix in the atrium. The same mixed blood will enter the lungs as the brain. Internal organs will receive less oxygen. The animal's activity will decrease).

What advice can we give to the frog? ( Suggested answer: the frog needs to preserve its three-chambered heart)

Let's summarize the lesson. Today in class we studied the structure of the internal organ systems of amphibians using the example of a frog, and compared its body with that of a fish.

At home, I suggest you try to simulate the system of working organs of a frog if it is under water. Think about how you need to change the constructed circuit.

Now let's check how well you have learned new material. Execute test"Wave". If the sign refers to fish, then raise the “wave” above the horizontal line; if it refers to amphibians, then raise it below the line.

1. Occupy an aquatic habitat.

2. They have two circles of blood circulation.

3. The body is covered with moist skin.

4. Venous blood collects in the atrium.

5. Gas exchange occurs in one organ.

6. The intestines are supplied with mixed blood.

Check with comments.

Homework

1) No errors in operation:

Answer the question

The frog's forebrain is better developed than that of fish, which is associated with the behavior of the animal. Using your own observations and sources of additional information, prove this statement by comparing the behavior of fish and amphibians.

2) 1 or 2 errors:

Answer the questions

Can a frog spend its entire life in water without going onto land?

What advice can you give to a frog who wants to have fish gills?

3) 3 or more errors:

Re-read the text on the handouts.

Try to recall what you read from memory and fill in the tables.