What is the biological significance of metamorphosis. Biological meaning of metamorphosis

Question 1. What development is called postembryonic?

Postembryonic development occurs after the birth or exit of the embryo from the egg and ends with the death of the organism.

Question 2. Compare direct and indirect postembryonic development. Give examples of animals with these types of development.

During direct development (in reptiles, birds, mammals), an organism of small size emerges from the egg shells or from the mother’s body, but with all the main organs characteristic of an adult animal already formed. Postembryonic development in this case is reduced mainly to growth and puberty.

During development with metamorphosis, a larva emerges from the egg, usually simpler in structure than an adult animal, with special larval organs that are absent in the adult state. The larva feeds, grows, and over time the larval organs are replaced by organs characteristic of adult individuals. Consequently, during metamorphosis, larval organs are destroyed and organs characteristic of adult animals appear.

Question 3. What is the biological significance metamorphosis?

The biological significance of metamorphosis is that at the larval stage the organism grows and develops not at the expense of the egg’s reserve nutrients, but it can feed on its own.

Question 4. What structural features of a tadpole indicate the relationship between amphibians and fish?

The larval form of amphibians is a tadpole, which is characterized by gill slits, a lateral line, a two-chambered heart, and one circle of blood circulation. These signs indicate the relationship between amphibians and fish. During the process of metamorphosis, which occurs under the influence of thyroid hormone, the tail resolves, limbs appear, the lateral line disappears, lungs and a second circle of blood circulation develop.

Question 5. Remember from your zoology course how development with incomplete and complete transformation (metamorphosis) differs.

Metamorphosis is a profound transformation in the structure of the body, as a result of which the larva turns into an adult insect. Depending on the nature of postembryonic development in insects, two types of metamorphosis are distinguished:

1. incomplete, when the development of an insect is characterized by the passage of only three stages - egg, larva and adult phase (imago);

2. complete, when the transition of the larva to the adult form occurs at the intermediate stage - the pupal stage.

Question 6. What stage of postembryonic development in vertebrates occupies most of life? Explain why.

The second period of postembryonic development is puberty (i.e., the period of maturity). In most vertebrates, it usually occupies most of life. During this period, the genital organs and secondary sexual characteristics intensively develop (sexual dimorphism clearly emerges); By the end of the period, sexual maturity occurs and animals are able to reproduce. Animal growth slows down during this period.

Question 7. Compare the concepts of “growth” and “development”. How are they fundamentally different?

The growth and development of an animal are interconnected, but not identical processes. Growth usually means an increase in the size of an organism and its mass. Growth is based on three different processes: cell division, an increase in their mass and volume, and an increase in intercellular formations. Growth is a quantitative measurement that occurs in the body of animals during the period of ontogenesis, which occurs until its full maturation. Not every increase in mass can be called growth. Growth occurs, as a rule, in young animals due to active metabolism and accumulation of protein in the body.

The development of an animal is understood as the complication of the structure of the body, the differentiation and specialization of its organs and tissues. The development of an animal begins with the fertilization of the egg and the formation of a zygote. The most important biological feature of the zygote is its ability to repeat the path of historical development traversed by its ancestors. Individual development The organism consists of embryogenesis and postembryonic development.

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Strictly speaking, metamorphosis is any transformation, transformation that occurs in the Universe. This term is quite general and is used in a wide variety of areas of scientific knowledge. In this article we will look at the concept from a biological point of view. Within the framework of the science of life, it is more correct to call the phenomenon “metamorphosis”, in the masculine gender; in what follows, both possible options will be used.

So, in biology, metamorphosis is a pronounced morphological change in a living organism, which necessarily occurs during its ontogenesis. The phenomenon is observed in both plants and animals. In the latter, metamorphosis occurs in most invertebrates and some vertebrates: cyclostomes, fish, amphibians. The essence of the process is the transformation of the larval organism (in animals) or some organs (in plants) in such a way that the resulting adult organism is radically different from the newborn in structure, physiology and life activity.

For animals, metamorphosis is not only a sharp change in the structure of the body. The phenomenon is accompanied by a change in the environment and living conditions. The life activity of an adult organism is completely different from that of the larval stages; the difference lies in the food consumed and many other details. we discover the critical importance of metamorphosis in nature, it reduces biological competition for food, habitat and other factors between organisms different generations one type.

Let's take a closer look at metamorphosis in animals. The most striking example would be, perhaps, the class of insects. Metamorphosis is characteristic of all representatives of this group. The process is either a complete transformation or an incomplete one. Complete metamorphosis involves three stages of development of the organism: a worm-like larva, a pupa (a stationary stage, during which the body of the larva is completely destroyed and a new body of an adult is formed) and an adult insect. This type of phenomenon is typical for Diptera (flies, mosquitoes), Hymenoptera (bees, bumblebees, wasps), Lepidoptera (butterflies), Coleoptera (ladybugs). With incomplete metamorphosis, only two stages of development are observed: the larva, which is morphologically similar to the adult, and, in fact, the adult insect. characteristic of Orthoptera (locusts, grasshoppers, mole crickets), Homoptera (aphids) and Hemiptera (bugs).

For higher plants metamorphosis is a modification of individual organs in connection with the functions they perform, and not a transformation of the entire organism. As a rule, rudimentary rather than fully formed organs enter the process. Metamorphoses of plants are also called modifications. These are, for example, bulbs (onions), spines (cactus), tendrils (grapes), rhizomes (ginger), tubers (potatoes) and much more. The significance of metamorphosis for plants lies in their adaptation to conditions environment. For example, spines found on plants living in hot climates, by their shape, help reduce evaporation from the leaf surface.

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