Postembryonic period in plants. Postembryonic development

And it continues until death. Postembryonic development is accompanied by growth. However, it can be limited to a certain period or last throughout life.

There are 2 main types of postembryonic development:

  1. direct development
  2. development with transformation, or metamorphosis (indirect development)

Direct postembryonic development- a type of development in which a born organism differs from an adult in smaller sizes and underdevelopment of organs. In the case of direct development, the young individual differs little from the adult organism and leads the same way of life as adults. This type of development is characteristic, for example, of reptiles, birds, and mammals.

During development with metamorphosis a larva appears from the egg, sometimes outwardly completely different and even different in a number of anatomical features from an adult. Often the larva leads a different way of life compared to adult organisms (for example, butterflies and their caterpillar larvae). It feeds, grows, and at a certain stage turns into an adult, and this process is accompanied by very deep morphological and physiological transformations. In most cases, organisms are not able to reproduce at the larval stage, however, there are a small number of exceptions. For example, axolotls - larvae of tailed amphibians - are able to reproduce, while further metamorphosis may not occur at all. The ability of organisms to reproduce in the larval stage is called neoteny.

There are also 3 periods of post-embryonic development: - juvenile (until the end of maturation) - pubertal (takes most of life) - aging (until death)

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body growth

The development of any creature in ontogenesis is characterized by an increase in body weight, i.e. presence of growth. Growth is a quantitative sign characterized by an increase in the number of cells and the accumulation of a mass of intracellular formations, the linear dimensions of the body. Body weight increases as long as the rate of assimilation exceeds the rate of dissimilation. According to the nature of growth, all living beings can be divided into 2 groups: with definite and indefinite growth. The first group includes insects, birds, mammals; to the second - mollusks, crustaceans, fish, amphibians, reptiles.

Influence of factors of external and internal environment on the growth of the body

The growth process in humans and animals is influenced by many exogenous and endogenous factors. For normal development, the body needs, first of all, good nutrition. Food should include the amount of proteins, fats, carbohydrates, and minerals required by age. The role of light is determined by its participation in the synthesis in the body

Postembryonic development of animals is divided into three periods:

4.1. Postembryonic period of animal development

Period of growth and shaping(pre-reproductive )

This period is characterized by the continuation of organogenesis that began in embryonic life and an increase in body size. By the beginning of this period, all organs have reached the degree of differentiation at which the young animal can exist and develop outside the mother's body or outside the egg membranes. From this moment, the digestive tract, respiratory organs and sensory organs begin to function. The nervous, circulatory and excretory systems begin their function even in the embryo. During the period of growth and shaping, the species and individual characteristics of the organism are finally formed, and the individual reaches the dimensions characteristic of the species. Later, other organs differentiate the reproductive system. When its formation ends, the second stage of postembryonic development begins.

maturity period(reproductive).

During this period of maturity, reproduction occurs. The duration of this period is different for different species of animals. In some species (mayflies, silkworm) it lasts only a few days, in others it lasts for many years.

old age ( post-reproductive).

It is characterized by a decrease in the intensity of metabolism and involution of organs. Aging leads to natural death.

4.2. Postembryonic period of human development

Postembryonic postnatal) period of human development, otherwise called postnatal, is also divided into three periods (Fig. 5):

Juvenile (before puberty);

Mature (adults, sexually mature state);

old age ending in death.

Otherwise, we can say that for a person it is also possible to distinguish pre-reproductive, reproductive and post-reproductive periods of post-embryonic development. It should be borne in mind that any scheme is conditional, since the actual state of two people of the same age can differ significantly. Therefore, the concept of chronological (calendar) and biological age has been introduced. Biological age is determined by a combination of metabolic, structural, functional features of the organism, including its adaptive capabilities. It may not correspond to the calendar.

Scheme 5

4.2.1. Juvenile period

According to the accepted periodization, the juvenile period begins after birth and lasts for women up to 21 years, and for men up to 22 years.

The first month of the child is considered neonatal period. The position of the child at this time resembles the position of the fetus in the uterus. Most of the day the baby sleeps, waking up only at the time of feeding. Caring for a child requires strict observance of the time of feeding and preferably with mother's milk, high purity, temperature not lower than 20 ◦ C.

From the first month to a year, the period of time is called chest.

During the first year of life in the child's body there are many changes in the motor system. At the end of the 1st month, he tries to straighten his legs, at one and a half months he raises and holds his head, at six months he sits, and at the end of the first year of life he tries to take his first steps. During this period, the child's psyche also develops. In the 2nd month, the baby smiles when the mother appears or when bright pictures are shown; by the 4th month he takes toys in his mouth, examining them, begins to distinguish between adults. In the second half of infancy, the child begins to understand many of the phrases of the parents. Active movements of the child at this time contribute to the development of the muscular and skeletal systems, better supply of the body with nutrients and oxygen, i.e. strengthening metabolic processes in the child's body, and most importantly, they normalize the activity of the nervous system. Water and air procedures are necessary during this period for the child.

Three rules must be followed by adults when caring for a child during this period: gradualness, repetition, regularity. A clear regimen of a child's life will develop conditioned reflexes in him, the formation of which makes it possible for the child to develop life skills that ensure high resistance of the organism to the action of adverse factors.

Early childhood- period from one to 3 years. During this period, the child grows intensively, eats the same food as adults, he develops a desire for independence and self-respect. He masters many new movements, imitates adults during the game.

Preschool period- period from 3 to 7 years. During this period, children show great interest in the world around them. Curiosity is so great that this period is also called the stage of questions: where? when? why? why? During this period, the brain continues to grow, inner speech is formed. An external manifestation of this is the child's conversations with himself and with toys. For a child during this period, play is important. It occupies the same place as an adult sports and work. Games develop the child and encourage him to be creative.

School period- period from 7 to 17 years. This period is divided into early(7-11 years old), average(11-15 years for boys and 11-14 years for girls) and older(15-17 years old). For the early school period, learning is already the main thing. This is a serious, intense work in mastering written language, in educating collectivism, in learning new things about the world around us, in mastering the experience accumulated by many generations of people. All this contributes to the harmonious mental, physical and volitional development of schoolchildren.

middle school The period is also called adolescence. In children, a profound restructuring of the activity of all organs and physiological systems takes place. This is due to puberty, with the intensive formation of sex hormones, which entails features of physical and physiological development, both in boys and girls. In adolescence, the development of speech ends, the formation of character and the moral formation of the personality take place.

Adolescents, as well as older schoolchildren, are characterized by accelerated rates of physical and sexual development, called acceleration. For example, in the 20s of our century, the growth of 14-year-old boys reached an average of 145.4 cm, in the 70s, growth reached 162.6 cm, body weight increased by an average of 13.5 kg. The average height and body weight of girls also increased markedly. The causes of acceleration have not yet been fully studied, but it has been found out that the physical development of modern children does not entail their moral and social maturation.

Thus, physiological, psychological and social maturity is distinguished. Physiological maturity is the puberty of the body. The term for achieving physiological maturity is individual. It depends on climatic, hereditary and other factors. Psychological maturity- this is the moral stability of girls and boys, self-control of behavior in the family and society. social maturity- this is a conscious attitude of a person to reality, this is the completion of a person's education, the beginning of labor activity, economic independence, this is, if necessary, the fulfillment of civic duty to the state.

The main stages of postembryonic development

Postembryonic or, as it is also called - postnatal, the period of human development is divided into three main periods:

  • juvenile, which lasts until puberty;
  • mature, including the period of adulthood in the sexually mature state;
  • a period of old age that ends with death.

These periods of postembryonic development can also be called:

  • pre-reproductive,
  • reproductive,
  • post-reproductive periods.

At the same time, the conditionality of this scheme should be understood, since the actual condition of people of the same age can vary greatly. For this, a classification of ages was introduced:

  • chronological or calendar,
  • biological.

The biological age of a person is determined by a combination of structural, metabolic, functional features human body, and its adaptive capabilities. This age may not correspond to the age indicated in the passport.

Juvenile period in human development

Remark 1

Juvenile period starts immediately after birth. It lasts for women up to about $21$ years, and for men a little longer - up to $22$ years.

The first month of a child's life is the neonatal period. The child at this time is in the position of the embryo, reminiscent of the position of the fetus in the uterus. Most of the child's life during this period passes in a dream.

The period from the first month to the year is called chest. The first year of a child's life is full of changes in the motor system. If at the end of the first month he only makes attempts to straighten his legs, then at a month and a half he can already raise and hold his head, by six months he sits, and takes his first steps at the end of the first year of life. During this period, the child's psyche is actively developing. In the second month of his life, the child begins to smile, by the fourth month he explores objects, taking them in his mouth, begins to distinguish between people. In the second half of the year, the child begins to understand some phrases. The active movements of the child during this period contribute to the acceleration of metabolic processes in the body of a growing child and normalize the work of the nervous system. During this period, for the correct development of the child, it is necessary to follow three rules: gradualness, repetition and systematicity. A clear mode of life allows you to develop conditioned reflexes.

Early childhood includes ages from one to three years. This is a period in which there is an active growth of the child, familiarization with food by adults, the manifestation of independence and the desire for self-respect. In early childhood, children master new movements, in the game they begin to imitate adults.

Preschool lasts three to seven years. This period is characterized by great interest in the surrounding reality and the manifestation of curiosity. During this period, the brain grows and inner speech is formed, which manifests itself in the child's conversations with himself or with toys. The game for the development of the child during this period is of great importance.

The period from seven to seventeen years is called school and is divided into early (period from $7$ to $11$ years), middle (period from $11$ to $15$ years for boys, from $11$ to $14$ years for girls) and senior (period from $15$ to $17$ years) . For the early school period, the main thing is the mastery of written language, the education of collectivism, knowledge of the new about the world around us, the assimilation of certain experience. Adolescents and older schoolchildren are characterized by rapid rates of physical and sexual development. This accelerated process is called acceleration.

Mature period in human development

Remark 2

The mature period of postembryonic development occurs in men at about $22 a year, and in women as early as $21 a year.

The period of adulthood can be conditionally divided into two stages:

  • up to $35$ years,
  • $36 to $60 for men and $36 to $55 for women.

In the period of $30-35$ years, certain changes in physiological reactions, changes in the level of metabolism are detected. These symptoms are precursors of involution. After $45$ years, a person has significant changes in endocrine functions. And after fifty years, changes occur that mark the beginning of the aging process.

human aging period

Remark 3

Aging in men begins after about $60 years, and in women after $55.

According to the modern classification of people during the aging period can be divided into the following groups:

  • $60$ - $76$ years - seniors,
  • $75$ – $89$ years - old,
  • over $90$ years - centenarians.

Definition 1

Aging- this is a natural stage of individual development, characteristic not only of man, but of all living organisms. Old age is studied by science - gerontology, which determines the patterns of aging and formulates recommendations for extending life.

There are certain signs of aging:

  • graying of hair, which, it should be noted in the population, begins after 30 years and is constantly progressing;
  • changes in skin texture and appearance skin;
  • change in posture;
  • loss of muscle strength;
  • tooth loss;
  • size is shrinking internal organs;
  • blood vessels lose their elasticity and blood pressure changes;
  • reduced immunity, ability to regenerate, heat generation;
  • hearing worsens and visual acuity decreases;
  • reaction time is reduced, memory weakens and performance decreases.

Regardless of the method of reproduction, a single cell gives rise to a new organism, containing hereditary inclinations and possessing all the characteristic features and properties of the whole organism.
Individual development consists in the gradual implementation of hereditary information received from parents.

Beginnings of evolutionary embryology put Russian scientists A.O. Kovalevsky and I.I. Mechnikov. They first discovered three germ layers and established the principles of development of invertebrates and vertebrates. Ontogeny, or individual development, is the entire period of an individual's life from the moment the zygote is formed to the death of the organism.

Ontogeny is divided into two periods:

- embryonic period: from the formation of a zygote to birth or exit from the egg membranes;
— postembryonic period: from the exit from the egg membranes or birth to the death of the organism.

Stages of embryonic development (using the example of a lancelet)

Splitting up - repeated division of the zygote by mitosis. The formation of a blastula is a multicellular embryo.

gastrulation - the formation of a two-layer embryo - a gastrula with an outer layer of cells (ectoderm) and an inner layer lining the cavity (endoderm). In multicellular animals, often after the formation of a two-layer embryo, a third germ layer appears - the mesoderm, which is located between the ecto - and endoderm.

The embryo becomes three-layered. The essence of the process of gastrulation is the movement of cell masses. The cells of the embryo practically do not divide and do not grow. The first signs of cell differentiation appear.

Organogenesis - formation of a complex of axial organs: neural tube, chord, intestinal tube, mesodermal someites. Further differentiation of cells leads to the emergence of numerous derivative germ layers - organs and tissues. From the ectoderm are formed: nervous system, skin, organs of vision and hearing. From the endoderm are formed: intestines, lungs, liver, pancreas. From the mesoderm - the notochord, skeleton, muscles, kidneys, circulatory and lymphatic systems.
In the course of organogenesis, some rudiments influence the development of other primordia (embryonic induction). The interaction of parts of the embryo is the basis of its integrity. During the period of embryonic development, the embryo is very sensitive to the influence of environmental factors. Harmful influences such as alcohol, tobacco, drugs can disrupt the course of development and lead to various deformities.

Post-embryonic or post-embryonic development begins from the moment of birth or exit from the egg membranes and lasts until the death of the organism. It is of two types: direct and indirect.

With direct development born offspring are similar in everything to adults, live in the same environment and feed on the same food, which intensifies intraspecific competition (birds, reptiles, mammals, some insects, etc.).

With indirect development a new organism is born in the form of a larva, which undergoes a series of transformations in its development - metamorphoses (amphibians, many insects). Metamorphosis is associated with the destruction of larval organs and the emergence of organs characteristic of adult animals. For example, in a tadpole, in the process of metamorphosis, which occurs under the influence of thyroid hormone, the lateral line disappears, the tail dissolves, limbs appear, lungs and a second circle of blood circulation develop.

Meaning of metamorphosis:

- larvae can feed on their own, grow and accumulate substances for the formation of permanent organs, living in an environment uncharacteristic for adults;

- larvae can play an important role in the dispersal of organisms (for example, bivalve larvae).

- different habitat reduces the intensity of intraspecific struggle for existence.

Indirect development of individuals is an important adaptation that arose in the course of evolution.

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Ontogenesis (from the Greek οντογένεση: ον - being and γένεση - origin, birth) - the individual development of an organism from fertilization to death.

In multicellular animals, as part of ontogenesis, it is customary to distinguish between the phases of embryonic (under the cover of the egg membranes) and postembryonic (outside the egg) development, and in viviparous animals, prenatal (before birth) and postnatal (after birth) ontogenesis.

In multicellular plants, embryonic development refers to the processes occurring in the embryo sac of seed plants.

The term "ontogeny" was first introduced by E. Haeckel in 1866. During ontogenesis, the process of realization of genetic information received from parents takes place.

Ontogeny is divided into two periods: embryonic - from the formation of a zygote to birth or exit from the egg membranes;

Embryonic period

In the embryonic period, three main stages are distinguished: crushing, gastrulation and primary organogenesis. The embryonic, or germinal, period of ontogenesis begins from the moment of fertilization and continues until the embryo emerges from the egg membranes. In most vertebrates, it includes stages (phases) of cleavage, gastrulation, histo- and organogenesis.

Splitting up

Cleavage - a series of successive mitotic divisions of a fertilized or initiated egg for development. Cleavage is the first period of embryonic development, which is present in the ontogeny of all multicellular animals and leads to the formation of an embryo called blastula (one-layer embryo). At the same time, the mass of the embryo and its volume do not change, that is, they remain the same as those of the zygote, and the egg is divided into ever smaller cells - blastomeres. After each cleavage division, the cells of the embryo become smaller and smaller, that is, the nuclear-plasma relations change: the nucleus remains the same, and the volume of the cytoplasm decreases. The process proceeds until these indicators reach the values ​​characteristic of somatic cells. The type of crushing depends on the amount of yolk and its location in the egg. If there is little yolk and it is evenly distributed in the cytoplasm (isolecithal eggs: echinoderms, flatworms, mammals), then crushing proceeds according to the type of complete uniform: blastomeres are the same in size, the whole egg is crushed. If the yolk is distributed unevenly (telolecital eggs: amphibians), then crushing proceeds according to the type of complete uneven: blastomeres are of different sizes, those that contain the yolk are larger, the egg is crushed as a whole. With incomplete crushing, there is so much yolk in the eggs that the crushing furrows cannot separate it entirely. Cleavage of an egg, in which only the “cap” of the cytoplasm concentrated on the animal pole, where the nucleus of the zygote is located, is crushed, is called incomplete discoidal (telolecital eggs: reptiles, birds). With incomplete surface crushing in the depths of the yolk, the first synchronous nuclear divisions occur, which are not accompanied by the formation of intercellular boundaries. nuclei surrounded by a small amount cytoplasm, evenly distributed in the yolk. When there are enough of them, they migrate to the cytoplasm, where then, after the formation of intercellular boundaries, the blastoderm (centrolecithal eggs: insects) appears.

Gastrulation is the process of division of the embryo into germ layers. During gastrulation, the cells of the embryo practically do not divide and do not grow. There is an active movement of cell masses (morphogenetic movements). As a result of gastrulation, germ layers (layers of cells) are formed. Gastrulation leads to the formation of an embryo called a gastrula.

Primary organogenesis

Primary organogenesis is the process of formation of a complex of axial organs. In different groups of animals, this process is characterized by its own characteristics. For example, in chordates at this stage, the laying of the neural tube, chord and intestinal tube occurs.

In the course of further development, the formation of the embryo is carried out due to the processes of growth, differentiation and morphogenesis. Growth ensures the accumulation of the cell mass of the embryo. During the process of differentiation, variously specialized cells arise, forming various tissues and organs. The process of morphogenesis ensures the acquisition of a specific form by the embryo.

Postembryonic development

Postembryonic development is either direct or indirect.

Direct development - development in which an organism that has appeared is identical in structure to an adult organism, but is smaller and does not have sexual maturity.

Embryonic and postembryonic development

Further development is associated with an increase in size and the acquisition of puberty. For example: the development of reptiles, birds, mammals.

Indirect development, or development with metamorphosis - the emerging organism differs in structure from the adult organism, is usually simpler, may have specific organs, such an embryo is called a larva. The larva feeds, grows, and over time, the larval organs are replaced by organs characteristic of an adult organism (imago). For example: the development of a frog, some insects, various worms.
Postembryonic development is accompanied by growth.

Phylogeny (from the Greek phylos - tribe, race and geneticos - pertaining to birth) - the historical development of organisms. In biology, phylogenesis considers the development of a biological species over time. Taxonomy, the classification of organisms by similarity, is based on phylogeny, but differs methodologically from the phylogenetic representation of organisms.

Phylogeny considers evolution as a process in which the genetic line - organisms from ancestor to descendants - branches in time, and its individual branches can specialize relative to a common ancestor, merge as a result of hybridization, or disappear as a result of extinction.

Topic 3.3 Post-embryonic development

Terminology

1.Amnion- the body of the embryo, surrounded by a water shell.

2. Metamorphosis- transformation into a period of development.

3. Growth certain- Growth is limited.

4. Growth uncertain- lifelong.

5. Divergence- divergence of signs.

6. Phylogenesis the historical development of organisms.

Postembryonic period of development

At the moment of birth or release of the organism from the egg membranes, the embryonic period ends and the postembryonic period of development begins, ending with the death of the organism.

Postembryonic development can be direct or accompanied by transformation - metamorphosis.

With direct development, an organism emerges from the egg membranes or from the mother's body, in which all the main organs characteristic of an adult organism (reptiles, birds, mammals) are laid. Postembryonic development in these animals is reduced mainly to growth and sexual maturation. During development with metamorphosis, a larva emerges from the egg, usually arranged more simply 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 animals.

Consequently, during metamorphosis, the larval organs are destroyed and organs appear that are inherent in adult animals.

For example, in ascidians (a type of chordates), a larva is formed that has all the main features of chordates: chord, neural tube, gill slits. The larva swims freely, and then attaches itself to a solid surface and undergoes metamorphosis: the tail disappears, the notochord and the neural tube disintegrate. Ascidia leads an attached lifestyle. The structure of the larva indicates their origin from chordates, leading a free lifestyle. In the process of metamorphosis, ascidians switch to a sedentary lifestyle, and therefore their organization is simplified.

The larval form of amphibians is a tadpole, which is characterized by gill slits, a lateral line, and one circle of blood circulation. In the process of metamorphosis, under the influence of thyroid hormone, the tail disappears, limbs appear, the lateral line disappears, lungs develop. Attention is drawn to the similarity of a number of structural features of the tadpole and fish.

An example of complete metamorphosis is the development of insects. Butterfly caterpillars or dragonfly larvae differ sharply in structure, lifestyle and habitat from adult animals. Thus, metamorphosis is associated with a change in lifestyle or habitat.

With incomplete metamorphosis, development occurs in some insects, such as a cockroach.

The significance of metamorphosis lies in the fact that the larvae can feed on their own and grow, accumulating cellular material to form permanent organs characteristic of adult animals. In addition, free-living larvae of attached animals play an important role in the distribution of the species and in the expansion of its range. A change in lifestyle or habitat during ontogenesis, due to the fact that the larval forms of some animals live in different conditions and have different food sources, reduces the intensity of the struggle for existence within the species.

In a number of cases, the processes occurring in individual development indicate events that took place in phylogenesis, i.e. the process of historical development of this species.

The postembryonic period of development has a different duration.

Ontogenesis. Embryonic and postembryonic development

For example, a mayfly in the larval state lives 2-3 years, and in the adult state 2-3 hours or 2-3 days. Adults do not feed due to the lack of mouthparts. After fertilization and oviposition, they die. In most cases, the postembryonic period is longer. In humans, it includes the stage of puberty, the stage of maturity and old age.

In mammals, there is a dependence of life expectancy on the duration of puberty and pregnancy.

Postembryonic development is accompanied by growth. Distinguish growth indefinite, continuing throughout life and certain, limited by some period. Indeterminate growth is observed in trees, molluscs. In many animals, growth stops shortly after reaching puberty.

biogenetic law

All multicellular organisms develop from a single fertilized cell. The development of embryos in animals belonging to the same type is largely similar. In the early stages of development, vertebrate embryos are very similar. These facts are confirmed by the validity of the law of germinal similarity: "Embryos show, already from the early stages, a certain general similarity within the limits of the type."

The similarity of the embryos of different systematic groups indicates the commonality of their origin. Later, in the structure of the embryos, signs of a class, genus, species, and, finally, signs characteristic of a given individual appear. The divergence of signs of embryos in the process of development is called embryonic divergence and is explained by the history of the development of a given species, reflecting the evolution of one or another systematic group of animals.

All stages of development are subject to change. Mutations affect genes that determine the structure and metabolism of embryos at the earliest stages of development. But the structures that arise in embryos play an important role in the processes of further development. Therefore, changes in the early stages usually lead to underdevelopment and death of the organism. On the contrary, changes in the later stages, affecting less significant characters, may be favorable to the organism and in such cases are picked up by natural selection.

The appearance in the embryonic period of development of signs characteristic of distant ancestors reflects evolutionary transformations in the structure of organs.

Numerous examples point to a deep connection between the individual development of organisms and their historical development.

This relationship is expressed in biogenetic law: Ontogenesis (individual development) of each individual is a multiple and rapid repetition of the phylogeny (historical development) of the species to which this individual belongs.

The biogenetic law played an important role in the development of evolutionary ideas. In a number of cases, changes that distinguish the structure of adult organisms from the structure of ancestors appear in the embryonic period.

In some cases, changes occur in the middle stages of development.

Thus, phylogenesis is based on changes occurring in the ontogeny of individual individuals.

The development of organisms and the environment. An organism cannot live outside its environment. The development of an organism outside the environment is just as impossible. For example, a chicken egg develops only at a certain temperature. Equally important is the ionic composition for the development of aquatic organisms. All species are not indifferent to the concentration of oxygen, the content of carbon dioxide, etc.

There are critical periods in the development of the embryo when the embryo is more sensitive to the action of external agents. The organism develops under conditions characteristic of individuals of a given species, and development is disrupted outside these conditions.

Thus, the effects of adverse factors on the body in most cases necessarily affect the development of offspring.

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The concept of postembryonic development

After the birth of the organism, the next stage of individual development begins. In biology, it is called the postembryonic or postembryonic stage of ontogenesis (postembryogenesis).

Definition 1

Postembryonic stage of development This is the period of development of an organism from the moment of birth to its death.

Some scientists consider postembryogenesis the period from the moment of birth to the onset of puberty and the ability to reproduce. But many organisms die after the reproduction stage. So this is more of a philosophical question than a scientific one.

At the stage of postembryonic development, the organism grows and develops. Recall that growth is an increase in the size of the body due to metabolism and cell division, and development is a qualitative change in the body. Scientists distinguish two types of postembryogenesis: direct and indirect.

Direct postembryonic development

Definition 2

Direct type of embryonic development - this is a type of individual development of organisms, in which the born individual as a whole resembles an adult ("imago-like").

Direct development occurs as a result of embryonization.

Embryoization is inherent in reptiles, fish, birds and mammals. The biological significance of this phenomenon lies in the fact that the animal appears (is born or hatches) at a higher stage of development. This increases its ability to withstand environmental factors. In placental mammals, some marsupials, sharks, scorpions, one of the embryonic membranes fuses with the walls of the expanded part of the oviducts (uterus) in such a way that nutrients, oxygen enter the embryo through the mother's blood, and metabolic products are excreted. The process by which such an embryo is born is called real live birth .

Definition 4

If the embryo develops due to the reserve substances of the egg in the middle of the mother's body and is released from the shells of the egg even in the genital tract of the female, then this phenomenon is called ovoviviparous .

It is observed in some species of snakes, lizards, aquarium fish, ground beetles.

Definition 5

If the embryo develops in an egg outside the mother's body and leaves it into the environment, then this phenomenon is called egg production .

It is characteristic of most reptiles, birds, arthropods, egg-laying mammals (platypus, echidna), etc. Direct development is inherent in some coelenterates, ciliates and low-bristle worms, crustaceans, spiders, scorpions, mollusks, cartilaginous fish, reptiles, birds and mammals.

Indirect postembryonic development

Definition 6

Indirect development (metamorphosis) - this is a process accompanied by profound changes in the structure of the body, due to which the larva turns into an adult (adult).

The processes of metamorphosis occur in several successive stages. At each of these stages (phases), the animal has certain characteristic features of the structure and functions. Transformations can be complete and incomplete (complete and incomplete metamorphosis).

For insects with complete transformation in development, the phases of egg, larva, pupa and imago (adult sexually mature individual) are distinguished. These are representatives of insects such as beetles, butterflies, hymenoptera, fleas. The pupal phase is of particular importance. At this stage, fundamental transformations of the internal organs of the larva and the formation of tissues and organs of the adult insect take place.

At incomplete transformation the phases of egg, adult-like larva and adult are distinguished. Incomplete metamorphosis is present in bedbugs, dragonflies, cockroaches, orthoptera, and lice.

Indirect development is known in many intestinal, flat, round and annelids, most echinoderm mollusks, bony fish and amphibians.

Growth and regeneration

During postembryonic development, organisms grow. This process, as mentioned above, occurs due to plastic exchange. It is also characteristic of the cellular level of organization of the living. Cell growth occurs during interphase.

The growth of organisms can be limited and unlimited. limited growth observed if the individual stops growing, having reached any size, gaining the ability to reproduce. It is inherent in all unicellular, arthropods, birds, mammals.

When unlimited growth an increase in the size and mass of organisms occurs until their death. This phenomenon is typical for most higher plants, multicellular algae, tape and annelids, mollusks, fish, reptiles. Depending on the characteristics of ontogeny and the structure of the integument of the body, unlimited growth can be continuous and periodic. The growth of living organisms depends on the characteristics of heredity and is regulated in plants by phytohormones, and in animals by hormones and neurohormones.

An important role in ontogeny is played by the body's ability to regenerate.

Definition 7

Regeneration - this is the ability of the body to restore the body of lost or damaged parts of the body, as well as to restore the whole organism from a certain part of it.

This property is a general biological quality and underlies the processes of vegetative reproduction. Different groups of living organisms have different ability to regenerate. The higher the level of organization of organisms, the lower the ability to regenerate. In birds and mammals, this quality is preserved only in the form of wound healing, bone fusion, restoration of certain cells and tissues.

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