Frog habitat
Frogs live in damp places: in swamps, wet forests, in meadows, along the banks of freshwater bodies or in water. The behavior of frogs is largely determined by humidity. In dry weather, some species of frogs hide from the sun, but after sunset or in wet weather, rainy weather It's time for them to hunt. Other species live in the water or near the water, so they hunt during the day.
Frogs feed on various insects, mainly beetles and dipterans, but they also eat spiders and ground animals. gastropods, and sometimes fish fry. Frogs lie in wait for their prey, sitting motionless in a secluded place.
When hunting main role vision plays. Having noticed any insect or other small animal, the frog throws out a wide sticky tongue from its mouth, to which the victim sticks. Frogs only grab moving prey.
Figure: Frog tongue movement
Frogs are active in the warm season. With the onset of autumn they leave for the winter. For example, the grass frog overwinters at the bottom of ice-free reservoirs, in the upper reaches of rivers and streams, accumulating in tens and hundreds of individuals. The sharp-faced frog climbs into cracks in the soil for the winter.
External structure of a frog
The frog's body is short, the large flat head without sharp boundaries merges into the body. Unlike fish, the head of amphibians is movably articulated with the body. Although the frog does not have a neck, it can tilt its head slightly.
Figure: External structure of a frog
Two large bulging eyes are visible on the head, protected over the centuries: leathery - upper and transparent movable - lower. The frog blinks frequently, while the moist skin of the eyelids moistens the surface of the eyes, protecting them from drying out. This feature developed in the frog in connection with its terrestrial lifestyle. Fish, whose eyes are constantly in the water, do not have eyelids. A pair of nostrils are visible on the head in front of the eyes. These are not only the openings of the olfactory organs. The frog is breathing atmospheric air, which enters her body through the nostrils. The eyes and nostrils are located on the upper side of the head. When the frog hides in the water, it puts them out. At the same time, she can breathe atmospheric air and see what is happening outside the water. Behind each eye on the frog's head there is a small circle covered with skin. This is the outer part of the hearing organ - eardrum. The inner ear of a frog, like that of fish, is located in the bones of the skull.
The frog has well-developed paired limbs - front and hind legs. Each limb consists of three main sections. In the front leg there are: shoulder, forearm And brush. The frog's hand ends with four fingers (its fifth finger is underdeveloped). In the hind limb these sections are called hip, shin, foot. The foot ends in five toes, which in the frog are connected by a swimming membrane. The limb sections are movably articulated with each other using joints. The hind legs are much longer and stronger than the front legs; they play a major role in movement. A sitting frog rests on slightly bent forelimbs, while the hind limbs are folded and located on the sides of the body. Quickly straightening them, the frog makes a jump. The front legs protect the animal from hitting the ground. The frog swims by pulling and straightening its hind limbs, while pressing its front limbs to its body.
All modern amphibians have naked skin. In a frog, it is always moist thanks to the liquid mucous secretions of the skin glands.
Water from environment(from reservoirs, rain or dew) enters the frog’s body through the skin and with food. The frog never drinks.
Frog skeleton
The skeleton of a frog consists of the same main sections as the skeleton of a perch, however, due to its semi-terrestrial lifestyle and the development of its legs, it differs in a number of features.
Pattern: Frog Skeleton
Unlike fish, the frog has a cervical vertebra. It is movably articulated with the skull. It is followed by the trunk vertebrae with lateral processes (the frog's ribs are not developed). The cervical and trunk vertebrae have superior arches that protect the spinal cord. At the end of the spine of the frog and all other tailless amphibians is a long tail bone. In newts and other tailed amphibians, this section of the spine consists of large number vertebrae movably articulated with each other.
A frog's skull has fewer bones than a fish's skull. Due to pulmonary respiration, the frog does not have gills.
The skeleton of the limbs corresponds to their division into three sections and is connected to the spine through the bones of the limb girdles. Forelimb belt - sternum, two crow bones, two collarbones And two blades- has the appearance of an arc and is located in the thickness of the muscles. Hind limb belt formed by fused pelvic bones and is attached tightly to the spine. It serves as a support for the hind limbs.
Internal structure of a frog
Frog muscles
The structure of the muscular system of a frog is much more complex than that of a fish. After all, the frog not only swims, but also moves on land. Through contractions of muscles or muscle groups, the frog can perform complex movements. Her limb muscles are especially well developed.
Digestive system of a frog
Digestive system amphibians have almost the same structure as fish. Unlike fish, its hind intestine does not open directly outward, but into a special extension called cloaca. The ureters and excretory ducts of the reproductive organs also open into the cloaca.
Figure: Internal structure of a frog. Digestive system of a frog
Respiratory system of a frog
The frog breathes atmospheric air. The lungs and skin are used for breathing. The lungs look like bags. Their walls contain a large number of blood vessels, in which gas exchange occurs. The frog's throat is pulled down several times per second, creating a rarefied space in the oral cavity. Then the air enters through the nostrils into oral cavity, and from there to the lungs. It is pushed back under the action of the muscles of the body walls. The frog's lungs are poorly developed, and skin respiration is as important for it as pulmonary respiration. Gas exchange is possible only when the skin is damp. If a frog is placed in a dry vessel, its skin will soon dry out and the animal may die. Immersed in water, the frog switches entirely to skin respiration.
Figure: Internal structure of a frog. Circulatory and respiratory systems of the frog
Circulatory system of a frog
The frog's heart is located in the front of the body, under the sternum. It consists of three chambers: ventricle And two atria. Both atria and then the ventricle contract alternately.
In the frog's heart, the right atrium contains only venous blood , left - only arterial, and in the ventricle the blood is mixed to a certain extent.
The special arrangement of the vessels originating from the ventricle leads to the fact that only the frog’s brain is supplied with pure arterial blood, while the whole body receives mixed blood.
In a frog, blood from the ventricle of the heart flows through the arteries to all organs and tissues, and from them through the veins it flows into the right atrium - this systemic circulation. In addition, blood flows from the ventricle to the lungs and skin, and from the lungs back to the left atrium of the heart - this pulmonary circulation. All vertebrates, except fish, have two circles of blood circulation: small - from the heart to the respiratory organs and back to the heart; large - from the heart through the arteries to all organs and from them back to the heart.
Metabolism in amphibians using the example of frogs
Metabolism in amphibians is slow. The frog's body temperature depends on the ambient temperature: it rises in warm weather and falls in cold weather. When the air becomes very hot, the frog's body temperature decreases due to the evaporation of moisture from the skin. Like fish, frogs and other amphibians are cold-blooded animals. Therefore, when it gets colder, frogs become inactive, try to get somewhere warmer, and during the winter they go into hibernation.
The central nervous system and sensory organs of amphibians using the example of a frog
The central nervous system and sensory organs of amphibians consist of the same sections as those of fish. The forebrain is more developed than in fish, and two swellings can be distinguished in it - cerebral hemispheres . Amphibians' bodies are close to the ground and they do not have to maintain balance. In this regard, the cerebellum, which controls the coordination of movements, is less developed in them than in fish.
Figure: Internal structure of a frog. Nervous system of a frog
The structure of the sense organs corresponds terrestrial environment. For example, by blinking its eyelids, a frog removes dust particles stuck to the eye and moistens the surface of the eye.
Like fish, the frog has an inner ear. However, in the air sound waves spread much worse than in water. Therefore, for better hearing, the frog has also developed middle ear. It begins with the sound-receiving eardrum - a thin round membrane behind the eye. From it, sound vibrations are transmitted through the auditory bone to the inner ear.
Amphibians, or amphibians, are cold-blooded predatory animals that thrive both in water and on land. Initially, they breathe using gills, and then adults switch to pulmonary breathing. The article will examine in detail the internal structure of amphibians using the example of a frog.
Habitat
Amphibians live in two environments: on land and in water, they jump well and swim well, and even climb trees. Thanks to their characteristics, they thrive both in damp places (swamps, wet forests and meadows) and on the banks of freshwater bodies. The entire development process takes place in water. There they reproduce, the development of larvae occurs, as well as the growth of fry, and only mature individuals are found on land.
The behavior of frogs also depends on the humidity of the environment. They can't stand it sunny weather, and in the evening and on rainy days they go hunting. Those that live in or near water also look for food during the daytime. With the onset of cold weather, animals burrow into the silt at the bottom of reservoirs and spend the entire cold season there. They can breathe through their skin, so there is no need to rise to the surface. Some animals winter time spend years on the surface of the earth, burrowing under heaps of fallen leaves and big stones. All processes in the body slow down and only with the arrival of warmth do they, even from a frozen state, return to normal life.
Characteristics of the external structure of the frog
Schoolchildren usually study the internal structure of a frog in 7th grade. However, first let’s get acquainted with the external structure. The frog's body consists of a head and a body with a length of 8 mm to 32 cm. The color can be solid (green, brown, yellow) or variegated. The cervical region is not pronounced, the head immediately passes into the body. The animal has developed fore and hind limbs. The skin is bare and mucous, the horny ones are poorly developed. The epidermis contains a large number of multicellular glands that produce a mucous substance that protects the skin from drying out. Typically terrestrial limbs of the five-fingered type have a complex muscular structure. Hind limbs due to the special method of movement, they have become more developed than the front ones, which consist of the shoulder, forearm and hand. There are four toes; males have a swelling at the base of the inner one, which is a genital wart. The long hind limb consists of a thigh, lower leg and foot, which has five toes connected by a swimming membrane.
frog head
On the flat head there are:
External and internal structure of a frog
The frog, like all amphibians, can be without water for a long time, but it needs it to reproduce. Having changed, the larvae lose their resemblance to fish and turn into amphibians. The body is elongated, there are two pairs of limbs. The head, which goes into the body, unlike fish, is capable of turning. The skeleton consists of bones, although there is a lot of cartilage; The spine has many vertebrae. There are no ribs, which means there is no chest. Thanks to its strong skeleton and developed muscles, the animal is adapted for life on land. The hind and forelimbs have three joints. The skin is smooth and contains many glands to moisturize it. The frog breathes through the lungs and skin.
Structure internal organs frog suggests the presence of a three-chambered heart, consisting of one ventricle and two atria, as well as two circulation circles. Food passes from the pharynx through the esophagus, stomach and short intestine. To digest it, secretions are produced by the liver, stomach walls and pancreas. At the end of the rectum there is a cloaca into which the female's oviduct opens. Animals have two kidneys and a bladder. The small braincase contains the developed forebrain and cerebellum. Frogs have organs of vision, hearing, touch, taste, and smell.
Internal structure of a frog
The muscles have a rather complex structure and are quite well developed compared to fish. Thanks to the coordinated work of a group of muscles, the frog can move, and in addition, they also take part in breathing.
The skeleton includes the following sections: spine, girdles and skeleton of the limbs, skull. The latter is connected to the spine using the cervical vertebra. This makes it possible to tilt your head. There are seven vertebrae in the trunk; there are no ribs. Sacral section, like the cervical one, is represented by one vertebra. The long bone forms the tail part. The thighs, legs, and feet form the hind limbs, and the shoulders, forearms and hands form the forelimbs. They are connected to the spine using a girdle of limbs: anterior and posterior. The first includes two shoulder blades and the sternum, and the second - pelvic bones, which have grown together.
Nervous system
The frog's nervous system is more complex than that of fish. Its internal structure is as follows: nerves, spinal cord and brain. The latter has three sections: a more developed, compared to fish, forebrain and a small cerebellum, since frogs lead a sedentary lifestyle and make only monotonous movements, as well as the cerebral hemispheres. Adults have developed upper and lower eyelids, as well as a nictitating membrane, thanks to which the cornea does not dry out and is protected from contamination.
Circulatory system
The circulatory system is represented by a three-chambered heart. From the lungs, arterial blood enters the left atrium. The right atrium receives venous blood from the internal organs, and arterial blood from the dermis.
With the simultaneous contraction of the atria, blood enters the ventricle. With the help of a special valve, venous blood flows to the lungs and skin, and arterial blood flows to the brain and head organs. It reaches all other organs, as well as parts of the body. mixed blood. The frog has two circles of blood circulation, and they are united by a common ventricle.
Respiratory system
The skin takes part in breathing, and the internal structure of the frog allows breathing with the help of the lungs, which have a network of blood vessels.
The frog opens its nostrils, the bottom of the oropharyngeal cavity drops and air enters it. Next, the nostrils close, and the bottom rises, and air enters the lungs. When the pulmonary walls collapse and the abdominal muscles contract, exhalation occurs.
Digestive system
It begins with a rather large oropharyngeal cavity. When it sees prey, the frog throws out its tongue and the prey sticks to it. Small teeth are located on the upper jaw and serve to hold prey. The structure and activity of the frog's internal organs contribute to the processing of food. She gets wet with secret salivary glands in the oropharyngeal cavity and enters the esophagus, and then into the stomach. Incompletely digested food enters the duodenum and then into the small intestine, where nutrients are absorbed. Undigested residues exit through the cloaca, having first passed through the rectum (hind) intestine.
Excretory system
On the sides of the sacral vertebra there are two kidneys that contain glomeruli and filter waste products and some nutrients from the blood.
The latter are absorbed in the renal tubules. Urine enters the bladder, having first passed through the ureters and cloaca. The internal structure of the frog allows the muscles Bladder contract as it fills. Urine enters the cloaca and then comes out.
Metabolism
It proceeds quite slowly. The frog's body temperature also depends on the ambient temperature. In cold times it decreases and increases in warm periods. IN extreme heat Due to the evaporation of moisture from the skin, the animal’s body temperature decreases. Due to the fact that these are cold-blooded animals, when cold weather sets in, they become inactive, choosing warmer places. And in winter they completely hibernate.
Sense organs
The structure and functions of the frog’s internal organs help it adapt to its living conditions:
- The frog is able to blink, having a movable upper eyelid and the so-called nictitating membrane. It moistens the surface of the eye and removes dirt particles stuck to it. The animal reacts more to moving object, and the motionless person does not see well enough.
- The hearing aid consists of the inner and middle ear. The latter is a cavity that opens on one side into the oropharynx, and the other goes to the surface of the head, separated from the external environment by the eardrum, which is connected to the inner ear with a stirrup. Through it, sound vibrations are transmitted to the inner ear from the eardrum.
- The animal is quite good at navigating by smell. Communicate with external environment sense of smell through the nostrils.
Conclusion
Thus, the peculiarities of the internal structure of the frog, like other amphibians, consist in a more complex structure of the nervous system, as well as sensory organs. In addition, they have lungs and two circulation circles.
Place of work, position:MAOU "Gymnasium No. 1" in Syktyvkar, teacher of biology and chemistry
Lesson topic: “Habitats and external structure of amphibians. Internal structure of amphibians using the example of a frog"
Tasks:
Educational:
- To develop students’ knowledge about the features external structure, skeleton and muscles of amphibians in connection with the terrestrial-aquatic lifestyle;
Educational:
- Development of curiosity and cognitive interest;
- Development of mindfulness;
- To develop the ability to compare the class of amphibians with the class of fish.
Educators:
- Aesthetic education;
- Upbringing careful attitude to nature.
Teaching methods:
- Verbal: story.
- Visual: printed tables “Type chordates. Class Amphibians", "Type Chordates. Class Amphibians. Frog", skeleton of a frog.
- Equipment: photocopies of frogs
Lesson type: Learning new material
Structure (elements) of the lesson with time indication:
- Organizational start of the lesson – 1 min.
- Learning new material - 20 min
- Laboratory work – 15 min
- Organization homework- 3 min
- Organized end of lesson – 1 min.
Literature for teachers:
- Naumov S.P. Vertebrate Zoology: A Textbook for Pedagogical Students. Institutes of Biology specialist. – 4th ed., revised. – M.: Education, 1982;
- Pepelyaeva O.A., Suntsova I.V. Biology. 7-8 grade: Lesson developments for textbooks Nikishova A.I., Sharova I.Kh.; Latyushina V.V. Shapkina V.A.; Konstantinova V.M. and others - M: VAKO, 2004
- I'm going to a biology lesson: Zoology: Fishes and Amphibians: A Teacher's Book. – M.: Publishing house “First of September”, 2000
Literature for students:
- Illustrated encyclopedia for schoolchildren. Zoology. World of encyclopedias - M., 2006;
During the classes
Teacher: Hello guys. Sit down. Open your notebooks and write downdate and topic of today’s lesson “Habitats and external structure of amphibians. Internal structure of amphibians using the example of a frog."
Guys, today we are starting to study a new class of vertebrates - Amphibians.
Amphibians, or Amphibians, are the first small group of primitive land animals that have retained a close connection with aquatic environment and numbering more than 2800 species of animals. The word "amphibian" means "two lives", as these creatures can live both on land and in water.Write it down in a notebook.
The habitats of amphibians are different, since I already noted above that they have retained a close connection with water. For example, some frogs are found along the banks of reservoirs in the summer, here they watch for insects, spiders, etc. Frogs feed only on moving insects. In case of danger, the frog jumps into the water and dives. After a while she floats up and if everything is calm she gets ashore. Amphibians are active only in warm weather, and with the onset of cold weather they sink to the bottom of reservoirs, bury themselves in silt and fall into torpor.
Newts and toads overwinter in ground shelters - wood dust, rodent burrows, and soil depressions.
When mastering new environment habitat, amphibians had to greatly change the structure of the body. The body of an amphibian, like a human, is 70% water, but their skin, unlike ours, is permeable to water.
Amphibians broke the law: those living on land must have dry skin. Disrespect for laws, as we know, is fraught with consequences. Punishment and amphibians awaited.
Which? How do they cope with this challenge?
Skin with scales is a useless breathing apparatus. You can breathe through your skin only when it is wet. And amphibians acquired glands that produce mucus. In toads and other amphibians, the skin glands secrete poisonous mucus that protects them from enemies. As a result, they became those who broke the law. The punishment is that they are caught in a vicious circle. Their wet skin is like an open water surface from which water evaporates easily. As water evaporates, it carries away heat with it. Always wet, amphibians lose heat hundreds of times more than they produce. So they live in the border zone of two environments, water and land. They stay near bodies of water, in damp places - there is little evaporation.
However, the skin, which makes the life of amphibians so difficult, also has a great advantage: it skillfully replenishes water reserves. Amphibians do not need to drink water by mouth. Those that live in streams, swamps, lakes absorb moisture with their entire skin. And in land animals, water delivery is carried out by certain areas of the skin. Neither toads nor other anurans need to look for a pond. They will fall with their bellies on the wet ground or walk on the grass wet with dew - and collect water.
It also turns out that the Russian fairy tale “The Frog Princess,” in which the frog sheds its skin, is not fiction, and even if it is fiction, it is very true. Skin is the only clothing of amphibians. In it they burrow into the ground, crawl into hollows, over stones. And no matter how much amphibians take care of their dresses, they become old and wear out. Not fabulous, ordinary frogs change their clothes at least four times.
In the water, the frog moves with the help of its hind limbs, between the toes of which a swimming membrane is stretched, which serves amphibians in the same way as flippers do for divers - they help them swim faster, since when sharply stretching and straightening the hind limbs, the frog makes strong pushes. Guys, why does a frog need its forelimbs?
Student: The frog lands on its front legs, while folding its hind legs.
Teacher: Right. Please note that the limbs of frogs are weak and not entirely of the terrestrial type.
Guys, please note that amphibians were the first to stand on their feet. The legs of amphibians have joints and are secured in the body with the help of limb girdles. They were the first to blink - to protect their eyes from damage and drying out, they developed movable eyelids. Like all terrestrial vertebrates, there are lacrimal glands, the secretion of which moistens the eyes, washes away dust particles and has a bactericidal effect. Note that the cornea of the eyes is convex (not flat like a fish) and the lens is lenticular (not round like a fish). Interestingly, in water, the cornea of amphibians becomes flat.
To hear better in air environment, amphibians have a new organ - the middle ear, closed by a flexible membrane - the eardrum - equipped with special bones to amplify and transmit the resulting vibrations.
Amphibians were the first of the terrestrial vertebrates to acquire a vocal apparatus. Males have vocal sacs (or resonators) located in the corners of their mouths, which, when croaking, inflate like bubbles, amplifying sounds. Females do not have sound amplifiers. They just squeak quietly.
Guys, let’s write down the conclusion in a notebook: The features of the external structure of amphibians depend on their access to land and on the fact that amphibians lead an aquatic and terrestrial lifestyle.
Guys, the most important changes have occurred in the skeleton of amphibians. And in order for us to better understand these changes, we will conduct laboratory work. Write down the name in a notebook laboratory work"Study of the frog skeleton." Next, draw a table in your notebook called “Structural features and significance of the frog skeleton.” Draw a table.
Skeletal departments | Name of the bones | Meaning |
Scull | Brain part Jaw bones | Brain protection |
Cervical – 1 vertebra Trunk – 7 vertebrae Sacral – 1 vertebra | ||
Skeleton of the forelimbs | Participate in movement |
|
Forelimb belt | Front limb support |
|
Skeleton of the hind limbs | Participate in movement |
|
Hind limb belt | Pelvic bones | Hind leg support |
Conclusion:
Homework: Paragraph 36. Learn the notes in the notebook, color the frog skeleton and paste it into the notebook, complete the table.
Student notebook sheet
11.02.2010
“Habitats and external structure of amphibians.
Internal structure of amphibians using the example of a frog"
“Amphibian” (“amphibian”) means “two lives,” as these creatures can live on both land and water.
Features of the external structure and lifestyle in connection with the terrestrial-aquatic lifestyle:
- The skin allows water to pass through;
- The body is covered with mucus;
- There are special glands that protect the skin from drying out;
- They move with the help of their hind limbs, between the toes of which there is a membrane;
- Movable eyelids;
- Middle ear;
- Eardrum;
- Voice apparatus;
- Convex cornea of the eyes.
Laboratory work
"Study of the Frog Skeleton"
“Structural features and significance of the frog skeleton”
Skeletal departments | Name of the bones | Meaning |
Scull | Brain part Jaw bones | Brain protection |
Spine (no thoracic septum) | Cervical – 1 vertebra Trunk – 7 vertebrae Sacral – 1 vertebra Caudal vertebra - urostyle | Protecting the spinal cord and supporting internal organs |
Skeleton of the forelimbs | Shoulder, forearm, hand (wrist, metacarpus, phalanges) | Participate in movement |
Forelimb belt | Paired scapulae, paired clavicles, paired caracoids | Front limb support |
Skeleton of the hind limbs | Thigh, lower leg, foot (tarsus, metatarsus, phalanges) | Participate in movement |
Hind limb belt | Pelvic bones | Hind leg support |
Conclusion: Due to life on land and movement by jumping, the frog skeleton is distinguished by a relatively wide skull, short spine, the presence of limb girdles, long hind and short limbs.
Frog (lat. rana) is a representative of the class of amphibians belonging to the order of tailless frogs, the family of true frogs.
Description of the frog.
All representatives of frogs do not have a pronounced neck; their head seems to have grown together with a wide and short body. The absence of a tail is reflected in the very name of the order to which these amphibians belong. On the sides of the large and flat head are bulging eyes. Like all land vertebrates, frogs have upper and lower eyelids. Under the lower eyelid you can find a nictitating membrane, the so-called third eyelid.
Behind each eye of a frog there is a place covered with thin skin (tympanic membrane). Two nostrils, which have special valves, are located slightly above the huge mouth with small teeth. The front legs of the frog, equipped with four toes characteristic of all amphibians, are quite short. The hind legs are highly developed and have five toes. The space between them is covered with a leathery membrane; the fingers of the limbs do not have claws.
The only excretory opening located in the back of the body is the cloacal opening. The frog's body is covered with bare skin, thickly lubricated with mucus, which is secreted by special subcutaneous glands. The frog's size ranges from 8 mm to 32 cm, and the coloring can be either single-color (brown, yellow, green) or variegated.
Types of frogs.
The entire diversity of these amphibians is represented by subfamilies:
- toad frogs;
- shield-toed frogs;
- African wood frogs;
- real frogs;
- dwarf frogs;
- disc-toed frogs.
In total, there are more than 500 species of frogs in the world. In the territory Russian Federation the most common are pond frogs and grass frogs. The world's largest frog reaches a length of 32 cm - this is the Goliath frog. The smallest frog in the world is the leaf frog, measuring 2 cm. In general, all types of frogs amaze with their diversity in size and color.
Where does the frog live?
The distribution area of frogs is huge. Due to the fact that representatives of this species are cold-blooded, it does not include areas with a critical climate. You won't see a frog in sandy deserts Africa, on the ice fields of Taimyr, Greenland and Antarctica. Some New Zealand islands were once not part of the frog's native areas, but now have distinct populations of the animals. The distribution of some species of frogs can be limited by both natural causes (mountain ranges, rivers, deserts, etc.) and man-made ones (highways, canals). In tropical conditions, the diversity of species is much greater than in areas with temperate or cold climates. Exist individual species frogs that are quite capable of living in salt water or even in the Arctic Circle.
The frog is a typical representative of amphibians. Using this creature as an example, you can easily study the most important characteristics class. To do this, we will look at the internal and external structure of the lake frog, which will further help us understand the structural features of all amphibians.
External structure
The external structure of a frog and its habitat are two inextricably linked links in a single chain. It's no secret that appearance and the structure is determined by the place and lifestyle of the animal.
The lake frog lives on the banks and in reservoirs, which is why it got its name. However, a river, swamp, pond and other places can also serve as a place of residence.
The external structure of the frog is very simple. The wide flat head turns into a small body with a reduced tail. The frog has very short forelimbs equipped with four fingers. The hind limbs, on the contrary, are elongated and have five fingers.
Covers of an animal
Speaking about the external structure of a frog, it is necessary to pay attention to its skin. The body of an amphibian creature is covered with smooth skin, on the surface of which there is an impressive number of glands that constantly secrete mucus. The secretion lubricates the surface, helping to retain moisture and promoting gas exchange. Mucus also protects the animal from penetration of harmful microorganisms into the body.
The amphibian's thin skin protects the body and also participates in gas exchange. Features of the external structure of the frog are associated with its lifestyle. For example, water enters the animal’s body only through the skin. It is for this reason that the frog must most time in dampness or water.
Characteristics of the external structure of the frog: body parts
Speaking about the external structure of the frog, we can distinguish the following parts of the body - the hind and forelimbs, the head and the torso. One of the features of the amphibian is the almost complete absence of a neck. In general, the separation line between the body and the head is not clear, or rather, it is practically non-existent. The frog's body is slightly larger than its head. The animal completely lacks a tail.
The large head has big eyes stick out. They are covered by clear eyelids designed to prevent damage, drying out and clogging.
Below the eyes are the nostrils. In general, it is worth noting that the eyes and nostrils are located close to each other at the top of the head for a reason. The fact is that while swimming they are constantly above the surface of the water. Thanks to this, the animal can breathe and see everything that happens above the lake.
The upper jaw of frogs is armed with a row of small teeth. But they don't have ears. Their role is played by the eardrums located behind the animal’s eyes.
Animal color
Describing the external structure of the frog, let us pay attention to its color, which is largely determined by its habitat. Most amphibians mimic external nature. And some varieties even have special cells that can change color skin depending on environmental conditions. Therefore, the color of the animal often repeats the pattern of the places where the creature lives.
In the tropics there are amphibians with bright colors. This indicates that the animal is very poisonous. This is what scares away enemies from such frogs.
Amphibian limbs
When presenting the external structure of the lake frog, we mentioned the unusual limbs of the animal. The peculiarity of their structure is due to the fact that the front legs are used for landing and for support in a sitting position. The hind limbs are much stronger and longer than the forelimbs. It is the hind legs that are used to move through water or on land. There are membranes on the limbs of the animal, which greatly facilitate movement in the water. The external structure of the frog is such that it allows the animal to move not only in water, but also on land.
Some representatives can even climb trees or glide in the air. Frogs have a lot of adaptations depending on their habitat. Nature has endowed some with special suction cups, thanks to which they stick to any surface, while others can remain under layers of sand or soil for a long time. In all these cases, their strong limbs help amphibians move.
The skeleton of a frog, according to biologists, is very similar to the skeleton of a perch. However, due to the nature of the lifestyle, there are significant differences. As we know, frogs have limbs. The front ones are attached to the spine with the help of peculiar bones. But the back ones are connected to the spine using hip bones. The amphibian representative is much simpler than that of fish, since it has fewer bones.
The frog's spine consists of a total of nine vertebrae. Moreover, it is divided into four sections: cervical, sacral, caudal and trunk. But the animal has no ribs.
Digestive system
Frogs and toads feed on insects and small invertebrates. Such animals are classified as predators. Sometimes they even disdain their relatives. Frogs guard their prey in a secluded place, motionless. As soon as the prey approaches, they shoot out their tongue and consume the prey.
Amphibian Blood
Blood is a connective tissue that plays a very important role in any organism. It is she who transports metabolic products and nutrients. As you know, blood consists of red blood cells and white blood cells.
The external structure and shape of frog red blood cells differs from human red blood cells. In the animal they are oval and have nuclei. But in humans, red blood cells are biconcave and lack nuclei. This increases the area occupied by oxygen molecules. Which means circulatory system people are more perfect. In addition, frog red blood cells are larger and there are much fewer of them than in human blood. All this suggests that amphibians require oxygen in much smaller quantities than mammals. And the reason for this is the ability to absorb part of the necessary oxygen by the surface of the skin.
It also has its own characteristics respiratory system frogs. Amphibians breathe not only with the help of their lungs. The skin also plays an active role in this process. As you can see, the outer covers play vital role in the life of amphibians. The lungs of an animal are thin-walled paired sacs that have a cellular internal structure and a highly branched network of blood vessels.
How does breathing occur? Amphibians use valves that close and open their nostrils. During inhalation, the nostrils open and the oropharyngeal cavity descends. This is how air gets inside. In order for it to get further into the lungs, the nostrils close, and the bottom of the oropharynx, on the contrary, rises. Exhalation is carried out due to the work of the walls of the lungs and the movement of the abdominal muscles.
Sense organs
The sense organs of amphibians have their own characteristics, due to the fact that animals also live on land. The lateral line organs help the frog navigate in space. The largest number of them is located on the head. Outwardly, they resemble two stripes that run along the body.
Temperature and pain receptors are located on the skin of amphibians. The nose as a tactile organ only works if it is located above the water. In water, the nostrils are always closed. Even the respiratory system is fully adapted to the amphibian’s habitat both in water and on land.
Nervous system of a frog
But the nervous system of amphibians is not very developed. It is in many ways similar to nervous system fish In this regard, amphibians are not far along the evolutionary ladder. The amphibian brain consists of five sections: the anterior, middle, intermediate, medulla oblongata, and cerebellum. By the way, the latter is poorly developed due to sedentary lifestyle animal life. But the forebrain consists of two hemispheres and, on the contrary, is quite developed.
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