How a tadpole turns into a frog for children. Development of a frog from egg to individual in an unnatural habitat under different external conditions. Fertilization occurring externally

After hibernation frogs and toads go to shallow ponds, ditches, puddles and spills well warmed by the sun melt water. Here the females lay eggs, very similar to fish eggs, and the males water them with seminal fluid.

As a rule, a lot of eggs are laid, with a reserve, because from the fertilization stage to the adult frog, their offspring face countless dangers. Unfertilized eggs become white or opaque. If everything went well, you can observe the division of the yolk into two, then into four, into eight, and so on, until it looks like a raspberry inside the jelly. Soon the embryo begins to look more and more tadpole-like, moving little by little inside the egg.
On average, the egg stage lasts about 6-21 days, until the larva hatches out. Most eggs develop in calm or still waters to prevent mechanical damage to the eggs.

Tadpole

Immediately after hatching, the tadpole feeds on the remains of the yolk, which is located in its intestines. On this moment The amphibian larva has poorly developed gills, mouth and tail. This is a rather fragile creature. The tadpole initially attaches itself to objects in the water using small sticky organs between its mouth and abdominal region.

Then, 7-10 days after the tadpole has already hatched, it will begin to swim and eat algae.

After 4 weeks, the gills begin to become overgrown with skin until they eventually disappear.
Tadpoles receive tiny teeth that help them scrape off algae. They have long had a spiral-shaped intestine, which makes it possible to extract from what they eat maximum amount nutrients. At this time, the tadpole has developed a notochord, a two-chambered heart and one circulation.
Interestingly, by the fourth week, tadpoles can be considered completely social creatures. Some are even able to interact with each other like fish!

Tadpole with legs

After about 6-9 weeks, the tadpole develops tiny legs and begins to grow. The head becomes more pronounced and the body lengthens. Now large objects, such as dead insects or plants, can also serve as food for the tadpole.

The forelimbs appear later than the hind limbs, with the elbow appearing first.

After 9 weeks the tadpole looks more like a small frog with a very long tail. The process of metamorphosis begins.

By the end of 12 weeks, the tail gradually disappears and the tadpole looks just like a miniature version of an adult frog. Soon he emerges from the water to begin adult life. And after 3 years, the young frog will be able to participate in the reproduction process.

Some frogs living on high altitudes or in colder places they can go through the tadpole stage much longer. Others exhibit unique developmental stages that differ from the traditional tadpole-in-water type life cycle.

Are the life cycles of a toad and a frog different?

In fact, toads are the same frogs. Toads just have a different name, look a little different, but they are all part of the frog family. Many people wonder what the difference is between the life cycles of toads and frogs. Perhaps the main difference is that frog eggs look like clumps, and toad eggs look like ribbons or stripes.

A frog turns into a prince only in a fairy tale. But don't the changes that occur to a frog during its life cycle demonstrate evolution? From a tadpole resembling a fish (even having gills), the “baby frog” quickly “transforms” into a completely new uniform to start leading a radically new lifestyle! The mouth becomes wider, the tail dissolves, but an “elastic” tongue is formed for catching flies, nostrils also appear, and the bulging eyes move to another place on the head. Finally, when the lungs finally mature and four legs grow, this mature tadpole celebrates its “coming of age” by jumping out of the water to now live on land.

This amazing transformation (metamorphosis) is far from just external. Almost all organs and systems of the body undergo radical restructuring. For example, a complete reconfiguration of the nervous system is required to control new or reprogrammed organs - eyes, ears, paws, tongue, etc. A similar reorganization must also occur at the biochemical level. Hemoglobin in the blood changes, the light-sensitive pigment in the eyes changes, among many other changes. Even the frog's excretory system changes to accommodate the new lifestyle.

Biologists are scratching their heads over the mega-complexity of this “rebirth” that occurs in ordinary ponds. A frog basking on a water lily leaf is the amazing result of many changes occurring successively with amazing precision in the right order. It would not be an exaggeration to say that the opening ceremony Olympic Games simply pales in comparison with the “choreography” of the process of frog metamorphosis. The life of a tadpole would certainly become more complicated if, for example, its tail disappeared before its legs grew. The same applies to his internal organs, bones, nervous system, biochemical processes, etc. Any failure can stall the entire process of reorganization of the body... and lead to rather unfortunate results (for the tadpole)!

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Very complex program

The fantastically complex information encoded in the DNA that allows a tadpole to transform into a frog clearly points to a Supreme Intelligence that created it. Such a program cannot be formed naturally; it demonstrates an initially intended end result.

All steps are interconnected

Years of research have uncovered multiple levels of processes required to accomplish this “life transformation.” For example, the disappearance of the tail requires precisely programmed micro-logistics operations. First, the tadpole stops the formation of tail muscle cells. It then produces a series of highly specific enzymes that dissolve the tail cells.

Then, at the right moment, these “little killers” are combined and injected into all types of tail cells. Finally, roving macrophages engulf these killed cells to then reuse their components and nutrients in other parts of the body (that is, the tail is not discarded, but is absorbed by the body).

"Change" does not mean "evolve"

So how substantiated is the claim that this is an example of “ evolution in action"? Is the transformation of a tadpole into a frog a clear example evolution?

Quite the opposite! Although the tadpole may look like a real "fish", from the moment it is born it is a frog. Everything he needs for rebirth (that is, all genetic information, schemes and programs), is already embedded in the DNA code stored in the nuclei of tadpole cells. At this micro level we find not only a complete plan for the development of the frog, but also a fully functional factory with all the necessary mechanisms and equipment to bring this plan to life.

The fish's genome does not contain the information necessary to become an amphibian, and there is nowhere for it to get such information.

This embedded information is the key difference between an evolutionary tale (that a fish evolved into an amphibian) and real world(in which the tadpole turns into a frog). From the very moment of its birth from an egg, the tadpole is already equipped with a full set of instructions “how to independently turn into a frog.” In contrast, a fish contains genetic instructions only for “building”... a fish! The fish's genome does not contain the information necessary to become an amphibian, and there is nowhere for it to get such information. In fact, it is doubtful that there is a single undisputed example of how evolutionary mechanisms have introduced new information into the genetic plan of a being.

This spring I was looking at frog eggs in a ditch on the property and thinking about how I could show Masha how frogs emerge from eggs. But I was afraid that I would destroy the future “princes” and “princesses”)).

But now, thanks to this article, I am theoretically savvy, and next spring I will definitely set up a frog incubator at my dacha. We will watch how frogs are made from eggs.

The grass frog is the most common amphibian in the central zone of our country. It is painted greenish-brown with all sorts of stains. It usually lives in floodplains of rivers, in forests, and quite far from water bodies. It is most active at dusk and at night, and spends the day on the forest floor. During rain and cloudy weather, it can be found during the day. The grass frog feeds on all kinds of insects, mollusks, and worms, and they also eat those inedible species that birds avoid. They happily catch mosquitoes that try to drink her blood.

They are connected only with bodies of water in early spring(during the breeding season) and in winter. At the end of September they move to their native reservoir for the winter. They climb under a snag at the bottom of the pond and fall asleep until next spring. There was a time when there were a lot of grass frogs within Moscow, especially in the floodplains of rivers. Now there are significantly fewer of them. The reason is banal - the deterioration of the environmental situation.

Frogs are food for many animals and birds. They are happily eaten by foxes, badgers, martens, storks, owls and... even hedgehogs. Thus, the energy stored in small animals (insects, mollusks, bugs, worms) enters a higher trophic level through frogs.

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Frogs are an interesting object for observing the development of an organism - from eggs to an adult animal. It’s a fascinating sight when before your eyes, in a fairly short time, a small frog turns out of caviar. If at someone’s home a child is interested in biology, nature can invite him to conduct such an experiment. Moreover, this biological “show” is, one might say, free. It will “occupy” the child for several months. To do this, they use frog caviar, which is collected in ponds, small lakes, and rivers.

The grass frog lays eggs at the end of April (at middle lane Russia) in shallow areas of ponds, ditches and puddles. IN southern regions- a bit earlier. The clutch is usually in the form of a slimy lump containing up to 1000 or more eggs. The eggs develop into tadpoles, and then into small frogs.

Experts noticed that twenty years ago the hatching of tadpoles from eggs within the city was almost one hundred percent. All the tadpoles were perfect. IN Lately the hatching percentage decreased sharply, and freaks began to appear among the tadpoles (one-eyed, with two tails, with one external gill, etc.), which ultimately died. Many tadpoles die without completing their development - turning into a small frog. All this is due to severe pollution of urban water bodies. However, for the sake of the child, you can go somewhere far from the city, where you can collect decent frog eggs in any body of water.

Frogs are interesting because any person (even a schoolchild) can hatch frogs from eggs at home and then release them into a pond. There is nothing complicated here, you just need to know some basic rules.

The spawning period for frogs begins in April and lasts about a week, after which adult individuals leave the pond and settle. And the caviar, accordingly, remains. Frogs return back to the pond only in the fall.

You need to take 1-2 lumps and place them in a small vessel (cup, basin) about 10 cm deep. After 1-2 days, embryos begin to develop from the eggs. At first, there will be small black dots inside the eggs (see picture), then something similar to a fish, and then you can see a creature inside the eggs that looks like a small tadpole.

After approximately 7-10 days (depending on water temperature), small tadpoles emerge from the eggs. On the sides of their heads they have branched external gills, with the help of which they breathe. During the first days, tadpoles stay on aquatic plants, attached to them with a suction cup. Soon they erupt a mouth, surrounded by horny jaws, with which they scrape off fouling leaves and pieces of the plants themselves.

I remember the incident. We lived at a biological station, cooked food in the kitchen, and washed dishes in the lake. That year there were a lot of tadpoles who “helped” us wash dirty dishes. They covered plates, pans, pots and ate leftover food. On such nutritious food, they grew quickly and left the pond much earlier (as it seemed to us) than the frogs from neighboring areas, which were not fed.

There must be a bush in the vessel aquatic plant, for example, Elodea, from which tadpoles scrape algae and bacteria. In laboratory conditions, tadpoles are fed with boiled eggs, dry milk, nettle infusion (small leaves are steamed with boiling water), and bread. They grow quickly on this food. However, it must be borne in mind that such food rots quickly, so it must be given little by little and removed periodically.

You can see how it progresses every day further development tadpoles. External gills do not last long. The tadpoles then develop gill slits with internal gills, like fish. He himself and outwardly becomes like a small fish. The tadpole retains this appearance for about a month. Then his hind limbs develop, and then his front limbs.

The lungs begin to develop, and the tadpole periodically rises to the surface to breathe with them. At this time, green leaves floating on the surface of the water should be placed in the vessel so that it is convenient for the tadpoles to climb out on them. His tail gradually becomes smaller, and his mouth, on the contrary, expands. Now the tadpole already resembles a frog in appearance. The baby frogs must be transferred to a vessel with high sides so that they do not escape. A similar incident happened at our house; we didn’t pay attention and the frogs scattered around the apartment. I had to get them out of all the corners and crevices.

At this time, the frogs do not eat anything. The size of such frogs reaches 2 cm; only a small tail reminds that this is a former tadpole. At this age they can be released into the reservoir, because... problems arise with feeding. At this time, they switch to animal food - they eat insects. But, if it is possible to grow small fruit flies, you can continue the process of observing small frogs. We had several large frogs living in our laboratory, which we fed with crickets (bought at a pet store).

Full development - from egg to frog - takes 2.5-3 months and depends on the water temperature and the quality of the food. Then the frogs begin a life full of dangers. They become adults only in the third year.

I immediately want to ask a question: what kind of fairy-tale frog princess was she? Most likely it was a grass frog. The tsars in Russia have always lived in the middle zone, but here only lake, pond, sharp-faced and grass frogs. The first two spend their entire lives in water and do not go far from bodies of water. And the frog princess, as you know, moved into the royal chambers. The sharp-faced frog is one and a half times smaller than the grass frog, and could hardly cope with an arrow, and its number is much smaller than the grass frog.

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Observing the development of frogs is an amazing sight. It allows us to understand how a living being develops from an egg. Before your eyes (before the eyes of a child) the development of a living being occurs. Mammals, including humans, develop in approximately the same way. After all, they all swim in water before leaving their mother’s womb. These observations help to understand the origin of terrestrial vertebrates, which also includes amphibians.

Amphibians live on land and breed in water. Their tadpoles, similar to fish, also live here (as in appearance, and by internal structure). Such similarities lead to the conclusion that amphibians and fish are related. The transitional form between fish and amphibians are lobe-finned fish, which were thought to have become extinct over 100 million years ago. However, in 1938 in Atlantic Ocean The first specimen of such a fish, which was named coelacanth, was caught off the southern coast of Africa.

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So, dear parents, get your children a living “toy”, frog eggs, which will captivate the children for several months, and maybe for life.

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Funds used to implement the project state support allocated as a grant in accordance with the order of the President Russian Federation dated March 29, 2013 No. 115-rp") and on the basis of a competition held by the Knowledge Society of Russia

The lesson allows you to repeat and expand children’s ideas about amphibians and their habitats, enrich their knowledge with new information about the life of frogs, teaches them to speak out, and fosters a caring and environmentally literate attitude towards animals.

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Lesson summary for preparatory group children

"HOW A TADPOLE TURNES INTO A FROG"

Main educational field: "Cognition"

Target: To arouse children's interest in objects of living nature, to form their ideas about the stages of development of some animals.

Equipment, materials, tools:Audio recording of frogs croaking, figurines of toy frogs, pictures depicting the stages of frog development (egg embryo - tadpole without legs - tadpole with two legs, tadpole with four legs and a tail - adult frog)

Progress of the lesson:

The teacher asks a riddle:

Shiny, big-eyed,

Lives in the lake, swims on the water.

He sits on the shore, looking at mosquitoes.

Green frog - big-eyed...

Children answer: frog

Educator: Children, do you know how frogs “talk”?

After the children’s answers, the teacher listens to an audio recording with the voices of frogs and shows figurines of toy frogs.

Then he shows a picture of tadpoles and asks the children if they know who is drawn in the picture and explains that this creature is called a tadpole because it has a large head.

The teacher explains that frogs in childhood are not very similar to adult frogs and invites the children to determine how a tadpole is and is not similar to an adult frog.

Then he invites the children to listen to a story about how frogs are born, which is accompanied by showing pictures and depicting the stages of frog development:

In one quiet transparent lake lived a large green frog. She really wanted to have baby frogs. Once spring came, the frog laid small transparent balls - eggs - on the shore of the lake. After some time, creatures with a small body, a large head and a tail emerged from the eggs. At first they didn’t even like the frog, because they weren’t very similar to their mother. After all, the frog itself did not have a tail, and its head was not that big, and most importantly, it had four legs. The tadpoles swam, ate and grew. Some more time passed, and first their hind legs appeared, and then their front legs. Now they had become more like an adult frog, although they still remained tadpoles with tails. Their mother couldn’t wait for the tadpoles to finally turn into real frogs. But the moment has come: the tadpoles have grown and become beautiful, green frogs with four legs and no tails. In the evenings they croaked with their mother, who was very proud of them.

After the story, the teacher discusses with the children how to arrange the cards depicting the stage of frog development so that they reflect what happened in the story. In conclusion, he emphasizes that frogs grow from tadpoles, which in turn emerge from eggs.

It is in the spring, in lakes, ponds, puddles, that you can see sticky, transparent balls with a black dot - frog eggs. At the end of the lesson, he invites the children to show how frogs jump and croak, and how tadpoles swim.

In this article we will look at the stages of frog development. But first, let's talk a little about what these creatures are. The frog belongs to the class of amphibians, the order of tailless.

Many people noticed that her neck was not pronounced - it seemed to have grown together with her body. Most amphibians have a tail, which the frog lacks, which, by the way, is reflected in the name of the order.

The development of a frog takes place in several stages; we will return to them immediately after we examine some of the features of these creatures.

What does a frog look like

For starters, the head. Everyone knows that the frog has rather large and expressive eyes located on both sides of its flat skull. Frogs also have eyelids; this feature is common to all terrestrial vertebrate creatures. The mouth of this creature has small teeth, and slightly above it there are two nostrils with small valves.

The forelimbs of frogs are less developed compared to the hind limbs. The first have four fingers, the second have five. The space between the fingers is connected by a membrane; there are no claws.

The development of a frog takes place in several stages:

1. Caviar throwing.
2. Early stage tadpoles.
3. Late stage tadpoles.
4. Adults.

Their fertilization is external - males fertilize eggs already laid by the female. By the way, there are species that lay more than 20 thousand eggs in one throwing. If everything goes well, then after ten days the tadpoles are born. And after another 4 months, they become full-fledged frogs. Three years later, a mature individual grows, which is completely ready for reproduction.

Now a little more about each stage.

Caviar

Now we will analyze all stages of frog development separately. Let's start with the very first thing - the egg. Although these creatures live on land, when they spawn, they go into the water. This usually happens in spring period. Masonry occurs in quiet places, at a shallow depth so that the sun can warm it up. All eggs are connected to each other, and this mass resembles jelly. From one individual there is barely one teaspoon of it. All this jelly mass is necessarily attached to the algae in the pond. Small species lay approximately 2-3 thousand eggs, large individuals - 6-8 thousand.

The egg looks like a small ball, approximately 1.5 millimeters in diameter. It is very light, has a black shell and greatly increases in size over time. Gradually, the eggs move on to the next stage of frog development - the appearance of tadpoles.

Tadpoles

After birth, the tadpoles begin to feed on the yolk, which still remains in small quantities in their intestines. This is a very fragile and helpless creature. This individual has:

• poorly developed gills;
• tail.

Tadpoles, in addition, are equipped with small Velcro, with the help of which they are attached to various aquatic objects. These Velcro are located between the mouth and abdomen. The babies remain attached for about 10 days, after which they begin to swim and eat algae. Their gills gradually become overgrown after 30 days of life and, eventually, are completely covered with skin and disappear.

It is also important to know that even tadpoles already have small teeth necessary to consume algae, and their intestines, arranged in a spiral, allow them to extract as much nutrients as possible from what they eat. In addition, they have a notochord, a two-chambered heart and a single circle circulation.

Even at this stage of frog development, tadpoles can be considered completely social creatures. Many of them interact with each other like fish.

Appearance of legs

Since we are considering the development of a frog in stages, the next step is to identify tadpoles with legs. Their hind limbs appear much earlier than their front ones, after about 8 weeks of development - they are still very tiny. During this same period, you may notice that babies’ heads become more distinct. They can now eat larger prey, such as dead insects.

The forelimbs are just beginning to form, and here we can highlight such a feature - the elbow appears first. Only after 9-10 weeks will a full-fledged frog be formed, although much smaller than its mature relatives, and even with a long tail. After 12 weeks it completely disappears. Now small frogs can go onto land. And after 3 years, a mature individual will form and will be able to continue its lineage. We'll talk about this in the next section.

Adult

After three many years, the frog can reproduce offspring into the world. This cycle in nature is endless.

To reinforce this, let us once again list the stages of frog development; the diagram will help us with this:

fertilized egg, represented by an egg - tadpole with external gills - tadpole with internal gills and skin respiration - formed tadpole with lungs, limbs and a gradually disappearing tail - frog - adult.