What is individual development in biology? Definition. Individual human development. Body type and physical activity

The individual development of organisms is a set of biological processes that determine the growth and change of cells throughout the entire period of their existence. The common scientific name is ontogenesis. Its main task is observation, identification of the main stages and features of each period, identification of patterns, as well as analysis of changes and identification of factors that these changes can cause.

It is inherent not only in humans, but also in all living beings and plants. The main ones are:

We will not consider the individual development of the plant organism in this short article, but dwell on the development of representatives of the animal world that is closer to man. The stages of development, as already mentioned, do not change in humans and correspond to those indicated above.

Gametogenesis in humans consists of two components: spermatogenesis (maturation of male germ cells - spermatozoa) and oogenesis (maturation of female germ cells - eggs). Fertilization is possible only under the condition of mature sex cells in the male and female individuals. When pathologies arise in fertilization, organisms can form - chimeras, some of which are quite viable.

Human embryogenesis is one of the most important stages. It is divided into the initial stage (0 - 1 week after fertilization), the actual embryonic stage (2 - 8 weeks) and the fetal or fetal stage (9 weeks - birth). It is during this period that vital organs are formed, the body is formed, genetic or other pathologies can manifest themselves.

The individual development of the body consists in the further development of organs, an increase in size and mass, the acquisition of new mental functions, a change in motor activity and the development of new types of it.

The postnatal period is the most important in the development of a new person. Its length is about 17 years (from newborn to adolescence). The individual development of the organism in this period is influenced not only by the characteristics due to heredity, but also by psychological and social factors. Consciousness, speech, thinking and other processes are formed. By the end of this period, new individuals, as a rule, come with completed gametogenesis.

Aging of the body is the stage of wilting, depletion of all the resources of the body. Irreversible disturbances in nerve cells occur, the quality of vision and hearing decreases, vital organs "wear out", the skin changes, the function of reproduction is lost and tissue regeneration sharply slows down, etc.

The individual development of a person, like any other organism, is ontogenesis with a phylogenetic program embedded in it, its periodization inevitably rests on the selection of a number of universal age processes (growth, maturation, development, aging), during which the corresponding age properties (differences) are formed. Both are generalized in the concept of age stages (phases, stages, periods) or stages of development (childhood, transitional age, maturity, old age, etc.). Age processes imply the question of how age properties are formed and in what way (gradually or abruptly, abruptly) the transition from one age stage to another occurs.

In modern science, there are three main terms for describing individual development as a whole - life time, life cycle, and life path. Although they are often used interchangeably, they differ substantially in content. The time of life, its length or space, denotes the time interval between birth and death. Life expectancy has important social and psychological implications. It largely determines, for example, the duration of the existence of generations and the duration of the primary socialization of children. The life cycle is more specific and meaningful. It assumes that the course of life is subject to a certain pattern, and its stages ("ages of life", or "times of life", similar to the seasons) are a constant cycle. The idea of a cyclical cycle of life, similar to the cyclical nature of natural processes (alternation of day and night, change of seasons, etc.). Many biological and social age processes are indeed cyclical. The body normally goes through the phases of birth, growth, maturation, aging and death. The personality assimilates, then fulfills and, finally, gradually leaves a certain set of social roles (work, family, parental), after which the same cycle is repeated by its descendants. Cyclicity also characterizes the change of generations in a society where the younger ones (children) first learn from the older ones, then actively act alongside them, and then, in turn, socialize the younger ones. The concept of a life path differs from a "life cycle" primarily in its multidimensionality, in that it presupposes many different trends and lines of development within the same biography, and these lines are simultaneously autonomous and interconnected. Its periodization is based on non-linear, once and for all phases, but specific life events. The timing, sequence and manner of any event in life, be it marriage or retirement, are as important as the fact that the event took place. This requires a combination of sociological, psychological and historical analysis. Thus, a meaningful characteristic of processes, properties and stages of individual development is possible either in the ontogenetic system, or in the life cycle system, or in the life path system. However, these systems are not side by side: the life path of an individual includes the life cycle of an individual, and this, in turn, includes ontogenesis.

The growth of the development of the human body

The processes of growth and development are influenced by a large number of a wide variety of endo - and exogenous factors. "Growth" and "development" are usually used as identical concepts, inextricably linked. Meanwhile, the biological nature of these processes is different, their mechanisms and consequences are different.

Growth is a quantitative increase in the biomass of an organism due to the geometric dimensions and mass of individual cells.

Development is a qualitative transformation in a multicellular organism due to differentiated processes (increasing the diversity of multicellular structures), which lead to qualitative and quantitative changes in the functions of the body.

The growth and development process is characterized by the following patterns:

1. Differentiation and integration of parts and functions, autonomization of development, increasing in the course of phyloontogenesis.

2. Dialectical unity of continuous and discontinuous; gradualness and cyclicality. Three main cycles in postnatal development can be noted on the human growth curve:

a) from birth to 10-13 years old with a constant decrease in speed;

b) pubertal spurt;

c) a drop in speed below the level before puberty and the cessation of growth.

The combination of periods of accelerated development and relative stabilization can be detected even in short periods of ontogenesis. For example, with long-term observation at weekly intervals of children from birth to 2 years. Non-linear growth (mini-jumps) is observed in about 70% of children and adolescents with a weekly examination for 6-10 months.

3. Heterochrony (difference in timing) in the maturation of different body systems (or tissues) and different signs within one system. According to the concept of system genesis by P.K. Anokhin, vital functions mature at a decisive pace, providing the primary formation of complex adaptive reactions that are specific for each specific stage of the body's relationship with the external environment.

4. Significant individual diversity of age dynamics for individual stages of ontogenesis, depending on the genetic program.

Topic 11. Periodization of individual development (ontogenesis)

Ontogenesis is a complex of successive transformations of an organism, starting from the stage of fertilization of an egg cell and up to the end of the life cycle.

Pythagoras (VI century BC) identified 4 periods of human life: spring (up to 20 years), summer (20-40 years), autumn (40-60 years) and winter (60-80 years), which corresponded to becoming, youth, blossoming and extinction.

Hippocrates divided the entire postnatal ontogeny into ten seven-year cycles.

Ontogenesis is subdivided into 2 periods: embryonic and fetal (fetal). During the first period, which lasts 8 weeks, the formation of organs and body parts characteristic of an adult occurs. In the fetal period, the size increases and organ formation ends. The growth rate of the fetus increases up to 4-5 months. After 6 months, the growth rate of linear dimensions decreases.

At the VII All-Union conference on age morphology, physiology and biochemistry, held in 1965 in Moscow, the following scheme of age periodization of human ontogenesis was adopted. This scheme has found wide application in anthropology, pediatrics, and pedagogy.

Scheme of age periodization of human ontogenesis

Newborn
Breast age	10 days - 1 year
Early childhood
First childhood
Second childhood	8-12 years old (boys) 8-11 years old (girls)
Adolescence	13-16 years old (boys) 12-15 years old (girls)
Adolescence	17-21 years old (boys) 16-20 years old (girls)
Mature age (1 period)	22-35 years old (men) 21-35 years old (women)
Mature age (2 period)	36-60 years old (men) 36-55 years old (women)
Elderly age	61-74 years (men) 56-74 years (women)
Old age
Centenarians	90 years and above

From the moment of birth, the neonatal period begins. During this time, the baby is fed colostrum for 8-10 days. The next period - breast - lasts up to 1 year. Its beginning is associated with the transition to "mature milk" nutrition. The length of the body increases from birth to one year, approximately 1.5 times, and the weight triples. From 6 months of age, milk teeth begin to erupt, and at 2-3 years of age, the eruption of milk teeth ends. During the first childhood, starting from the age of 6, the first permanent teeth appear. During the period of the second childhood, gender differences in body size and shape are revealed, and increased growth in length begins. On average, by the age of 12-13, boys and girls have finished changing their teeth. Secondary sexual characteristics begin to develop. The next period - adolescence - is called the period of puberty, or pubertal, by the end of which the body size is 90-97% of its final size, and the main functional characteristics of adolescents are close to the characteristics of an adult organism. During adolescence, the process of growth and formation of the organism ends, all the main dimensional characteristics reach a definitive (final) value. In adulthood, the shape and structure of the body changes little. Between the ages of 30 and 45-50, the body length remains constant, and then begins to decrease. In old and senile age, involutive changes in the body occur.

Topic 12. Puberty growth spurt

An important event in the puberty period is spurt - an abrupt increase in growth, observed in boys on average at 13-15 years old, and in girls at 11-13 years old. During this time, the absolute growth rate is unstable and gradually decreases: in boys - from 12 to 7 cm / year, in girls - from 11 to 6 cm / year.

Many factors are involved in the implementation of the growth spurt, and primarily sex hormones and growth hormone - STH, which exerts its effect through somatomedins - peptides synthesized in the liver. In addition to these hormones, the universal anabolic hormone insulin and thyroid hormones - thyroxine and triiodothyronine - are essential in this period. Insulin regulates protein and fat metabolism, and thyroxine and triiodothyronine affect the growth and differentiation of tissues, increasing the intensity of basal metabolism and heat production. The maturation of the reproductive function is completed by the age of 18-20.

Morphological maturation of the frontal cortex is achieved only by 12 years, and the final formation of the cerebral hemispheres - at 20-22 years. For the puberty period, the following are considered characteristic: an increase in subcortical influences and a weakening of the activity of the cerebral cortex, a violation of the vegetative sphere, increased emotionality, especially in girls.

The process of individual development of any organism is called ontogenesis... The concept of ontogeny was introduced into biology by Ernst Haeckel in 1866. According to modern concepts, ontogenesis (Greek ontos - being, individual, genesis - development) is a complete cycle of individual development of each individual, which is based on the implementation of hereditary information at all stages of existence in certain environmental conditions; it starts with education zygotes(with sexual reproduction) and ends in death. The biological species Homo sapiens is characterized by direct intrauterine development.

Depending on the environment in which the human body develops, ontogenesis splits into two large periods, separated from each other by the moment of birth:

Intrauterine(prenatal, or antenatal), when a newly born organism develops in the womb; this period lasts from conception to birth.
Extrauterine (postnatal) when a new individual continues its development outside the mother's body; this period lasts from the moment of birth to death.

Recently, it has also been proposed to highlight prezygous the period preceding the formation of the zygote.

Prezygotic period

Prezygotic period development is associated with the formation of gametes (gametogenesis). The formation of oocytes begins in women even before their birth and is completed for each given oocyte only after its fertilization. By the time of birth, a female fetus in the ovaries contains about two million first-order oocytes (these are still diploid cells), and only 350 - 450 of them will reach the stage of second-order oocytes (haploid cells), turning into eggs (one at a time during one menstrual cycle ). Unlike women, sex cells in the testes (testes) in men begin to form only at the onset of puberty. The duration of the period of sperm formation is approximately 70 days; per gram of testicle weight, the sperm count is about 100 million per day.

Fertilization is the process of fusion of an egg and a sperm cell, leading to the formation of a zygote. Fertilization of the egg takes place in the initial section of the fallopian tube, where only about a hundred spermatozoa penetrate. The ability of sperm to fertilize in the female genital tract lasts for two days. The sperm has an acrosome in the head, which contains an enzyme to dissolve the egg shell. When the sperm and egg come closer together, the acrosome ruptures, and the released enzymes dissolve the membrane of the female gamete. The sperm cell penetrates into the egg cell, after which it becomes covered with a dense membrane that prevents the penetration of other male gametes. As a result of fertilization, the diploid set of chromosomes is restored. The resulting unicellular embryo is a zygote. In it, during the day, complex movements of individual sections of the cytoplasm and its organelles occur.

Intrauterine period human development lasts 280 days and is divided into:

initial period(the first week after fertilization, during which the zygote is fragmented, the blastula is formed and implanted into the wall of the uterus);
embryonic period(the first two months), when the initial development of the embryo (embryo) occurs and when the main laying of tissues and organs takes place;
fetal period(3 -9 months), when the growth of the parts formed in the embryonic stage continues and the further formation of organs and systems. From the third month, the human embryo is called the fetus.

Initial period

Initial period. Splitting up- this is the initial stage of development of a fertilized egg (zygote). In humans, it lasts 3-4 days (the zygote is cleaved by a series of successive mitoses, but without the growth of daughter cells to the size of a zygote). In humans, the cleavage of the zygote is complete and uneven... The cells formed as a result of cleavage are called blastomeres... The result of the cleavage stage is the formation of a multicellular embryo - morula... Crushing and formation of morula occurs as the embryo moves along the fallopian tube. Morula enters the uterus, where the process takes place blastulation... Blastomeres in the morula repel each other, move to the periphery and line up in one layer, and by the 6th day a single-layer embryo in the form of a bubble is formed. Different blastomeres divide at different rates. Some of them (lighter) are located on the periphery, others (dark) are in the center.

The surrounding embryo is formed from light cells trophoblast, whose cells play an auxiliary role and do not directly participate in the formation of the body of the embryo. Trophoblast cells are able to dissolve tissues, due to which the embryo is introduced ( implanted) into the wall of the uterus. Further, the trophoblast cells exfoliate from the cells of the embryo, forming a bubble around it. The trophoblast cavity is filled with fluid that diffuses into it from the tissues of the uterus. From dark cells is formed embryoblast that looks like a knot. As a result of further cleavage of the embryoblast, the embryo takes the form of a disk spread out on the inner surface of the trophoblast. This stage of development of the embryo, when the trophoblast and embryoblast are secreted, is called blastocyst... Blastocyst, once in the uterine cavity, implanted getting nutrients from the wall of the uterus. Trophoblast cells differentiate into two layers. From the cells of the outer layer of trophoblast, trophoblast villi that grow into the epithelium of the uterus. This layer of villi forms the outermost shell of the embryo - chorion... Chorion plays an important role in the nutrition of the developing embryo and the removal of its end metabolic products. At later stages, this function is performed by placenta... In the inner layer of trophoblast cells, two cavities are formed; the walls of these cavities give rise to two more embryonic membranes - amnion and yolk sac. Amnion is a thin shell that covers the embryo and performs protective functions; its cells secrete amniotic fluid filling the amniotic cavity located between the amnion and the embryo. As the embryo grows, the amnion expands so that it is always pressed against the wall of the uterus. The amniotic fluid supports the embryo and protects it from mechanical damage. The yolk sac in the human embryo does not play a significant role, it is a kind of rudiment (the yolk sac is especially developed in reptiles and birds; it absorbs nutrients stored in the yolk and transfers them to the midgut of the embryo). In humans, the yolk sac contains practically no yolk, its main function is hematopoiesis... In addition, primary germ cells are formed in its wall, then migrate to the rudiments of the gonads.

The embryonic period

The embryonic period consists in the flow gastrulation and education three germ layers, histogenesis (tissue bookmarks) and organogenesis (organ bookmarks).

Gastrulation- This is the process of formation of germ layers. A disc-shaped embryoblast is called germinal disc... An embryo develops from it. The cells of this disc at an early stage, when its diameter does not reach 2 mm, differentiate into two germ layers (leaves) - ectoderm and endoderm... At a later stage, mesoderm. These three germ layers give rise to all tissues of the developing embryo. At the end of gastrulation in the 4th week, rudiments are formed neural plate and chords.

In the early stages of development, the exchange between the embryo and the maternal organism occurs due to the villi of the trophoblast, and then the fourth shell develops - allantois... Allantois grows outward until it comes in contact with the chorion, forming a vascular-rich structure that is involved in the formation of the placenta.

Placenta has the appearance of a disk, strengthened in the uterine lining, and from the 12th week of development, it fully provides an exchange between the fetus and the mother. By the end of the eighth week, all internal organs are laid. In the placenta, the blood of the mother and the fetus does not mix. Between the body of the embryo and the placenta is formed umbilical cord, in which two umbilical arteries carrying venous blood from the embryo, and one umbilical vein carrying arterial blood from the placenta to the fetus. Tissues are formed and differentiated from the cellular material of the embryonic primordia. This completes the embryonic period. An eight-week-old embryo is 3-3.5 cm long and weighs about 4 grams. His neck is isolated, facial features are outlined, limbs and external genitals are formed.

Fetal period begins from the 9th week of intrauterine life with a predominance of growth processes and final tissue differentiation. By the end of 3 months, the fetus weighs about 40 grams, its length reaches 8-9 cm. Ossification nuclei appear in almost all bones. On the 4th month, the individual features of the face are formed. At the 5th month, the skin becomes covered with fluff, the movements of the fetus are felt by the mother. The fetal heartbeat is heard, which is more frequent than that of the mother. At 6 months, the embryo is 30 cm long and weighs 650-700g. In the case of premature birth at 7 to 8 months, the fetus is viable, but needs the conditions of intrauterine life. By the end of the 9th month, the fluff on the skin is lost, but a layer of cheese-like lubricant remains, the nails protrude above the fingertips, the arms are longer than the legs, in boys the testicles descend into the scrotum. Fruit weight is about 3.5 kg and length is 50 cm.

The development of the fetus ends childbirth(expulsion of the fetus and placenta from the uterus). The onset of labor is associated with the release of a hormone by the pituitary gland. oxytocin causing strong contractions of the muscles of the uterus and abdominal muscles. The child is pushed into the small pelvis and is born into the world. The first sign of pulmonary respiration is a cry. After 15-20 minutes, the placenta with the amniotic membrane is separated from the uterine wall and pushed out.

In the process of embryogenesis, a developing organism can be affected by various factors (poisons, radiation, vitamin deficiencies, oxygen starvation, etc.) and cause developmental deviations in the form of anomalies and deformities. The violation of living conditions is especially dangerous if it coincides with periods of increased sensitivity of the embryo, the so-called critical periods of embryogenesis.

In humans, the 7th day, 7th week and childbirth are considered critical periods. Therefore, a pregnant woman must be protected from any adverse effects from the very first days of pregnancy.

Extrauterine (postembryonic) period.

From the moment of birth to death lasts extrauterine (postembryonic, postnatal) development.

The following periods are distinguished (the periodization of ages was adopted at the VII international symposium on the problems of age morphology, physiology and biochemistry in 1965):

newborn(first 1 - 10 days after birth),
chest(from 10 days to 12 months),
early childhood(from 1 to 3 years old),
first childhood(from 4 to 7 years old),
second childhood(from 8 to 12 years old),
adolescence(from 13 to 16 years old),
adolescence(from 17 years old to 21 years old),
period of maturity(from 22 years old to 55-60 years old),
elderly age(from 56-61 to 74 years old),
senile period(75 - 90 years old)
centenarians ( over 90 years).

The most intensive growth and development of the child is observed in the first year of life and during puberty. In the process of growth and development, the proportions of the body change. For example, the ratio of the size of the head to body in a newborn is 1: 4, while in an adult it is 1: 8.

The main features of humans in comparison with animals are the presence of thinking, speech and motor activity, which is closely related to work activity. For the development of these functions, the correct upbringing of children aged 2 to 4 is very important. The period of time from 7 to 18 years of age is a decisive period for the physical, mental and moral development of a person.

Back to Human Development

Development of the human body. Individual human development (ontogenesis) begins from the moment of fertilization, when the fusion of the female (ovum) and male (sperm) germ cells occurs. The initial stages of development take place in the genital tract of a woman, therefore, the entire ontogenesis is usually divided into prenatal and postnatal (from Lat. Natus - childbirth) periods, i.e. prenatal and postnatal.

In the prenatal (intrauterine) period of ontogenesis, in turn, the embryonic (embryonic) and fetal (fetal) periods are distinguished. The first lasts 2 months, the second - from the 3rd to the 9th inclusive.

The physical development of an individual is characterized by the weight, height and size of individual body parts.

These indicators change unevenly throughout life.

Accelerated growth is observed during early childhood (from 1 to 3 years), at the age of 5 to 7 years and during puberty (from 11-12 to 15-16 years), while the main body proportions also change. In parallel with growth, age-related changes are observed in all organs and systems. By about the age of 20-25, the growth of a person stops and a relatively stable period of existence begins - adulthood. After 55-60 years, a person begins to age gradually, and sclerotic changes appear in a number of organs. This, in turn, causes a decrease in various body functions.

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These indicators change unevenly throughout life.

In the process of development and growth of the organism and the formation of its nervous system, the nature and level of human needs changes. A newborn is dominated by vital needs associated with the implementation of vital functions: nutrition, breathing, sleep, etc. Gradually, various physiological needs associated with movement in space, with the assimilation of various nutrients, growth and development, as well as independent performance and voluntary regulation of physiological functions. Relatively early, already in the first year of life, cognitive needs begin to form, especially during early childhood (1-3 years) and later during the preschool and school periods of the child's development. The formation of social and communicative needs takes a fairly long period of ontogenesis, including the mature life of an individual.

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Ontogenesis - the individual development of an organism

1. What is ontogeny?
2. What is the set in the zingot?

Ontogenesis.

The process of individual development of an individual from the beginning of its existence to the end of life is called ontogenesis. Have bacteria and the simplest ontogenesis practically coincides with cell cycle and begins with the emergence of a unicellular organism as a result of the division of the maternal, and ends with the next division of this organism or death from adverse influences.

In multicellular species that reproduce asexually, ontogenesis begins with the isolation of a group of cells of the maternal organism (remember, for example, hydra budding), which, sharing mitosis, form a new individual with all its systems and organs.

In those species that reproduce sexually, ontogenesis begins from the moment fertilization ovum and the formation of a zygote - the first cell of a new organism.

Ontogeny is not just the growth of a small individual until it turns into a large one. This is a chain of strictly defined complex processes at all levels of the organism, as a result of which the structural features, life processes, and the ability to reproduce inherent only to individuals of this type are formed. Ontogenesis ends with processes that naturally lead to aging and death.

With the genes of the parents, the new individual receives a kind of instructions about when and what changes should occur in the body so that it can successfully go through the entire life path. Thus, ontogeny is the realization of hereditary information.

Types of ontogenesis.

In animals, three types of ontogenesis are distinguished: larval, ovipositor, and intrauterine development.

The larval type of development is found, for example, in insects, fish, amphibians. There is little yolk in their eggs, and the zygote quickly develops into a larva, which feeds and grows on its own. Then, after some time, metamorphosis occurs - the transformation of the larva into an adult (Fig. 54). In some species, there is even a whole chain of transformations from one larva to another and only then into an adult.

The meaning of the existence of larvae may lie in the fact that they eat a different food than adults, and, thus, the food base of the species expands. Compare, for example, the nutrition of caterpillars (leaves) and butterflies (nectar) or tadpoles (zooplankton) and frogs (insects). In addition, many species actively colonize new territories during the larval stage. For example, the larvae of bivalve molluscs are capable of swimming, while the adults are practically immobile.

The ovipositor type of ontogeny is observed in reptiles, birds and oviparous mammals, the eggs of which are rich in yolk. The embryo of such species develops inside the egg; no larval stage.

The intrauterine type of ontogenesis is observed in most mammals, including humans. In this case, the developing embryo is retained in the mother's body, a temporary organ is formed - the placenta, through which the mother's body provides all the needs of the growing embryo: respiration, nutrition, excretion, etc. Intrauterine development ends in the process of childbirth.

Periods of ontogenesis.

Any type of ontogenesis in multicellular animals is usually divided into two periods: embryonic and postembryonic.

The embryonic period begins with fertilization and is the formation of a complex multicellular organism in which all organ systems are represented. This period ends with the release of the larva from its membranes (with the larval type), the release of the individual from the egg (with the ovipositor type) or the birth of the individual (with the intrauterine type of ontogenesis).

The postembryonic period begins with the completion of the embryonic one. It includes puberty, adulthood, aging and ends in death.

The periods and timing of ontogenesis are very different for different groups of living organisms. For example, in very many vertebrates, the individual is in an adult state for most of its existence. In contrast, in many insects, the adult stage is the shortest and lasts only a few hours, necessary for the reproduction of offspring. There are great differences in the life cycles of animals, plants and fungi.
Ontogenesis. Types of ontogenesis. Metamorphosis. Placenta.

1. What is the difference between ontogeny of unicellular organisms and ontogenesis of multicellular organisms?
2. What types of ontogenesis are distinguished in animals? What are their features?
3. How does the embryonic period of embryogenesis in a crocodile end?
4. What are the functions of the placenta?

The ability of some animals to reproduce sexually in the early stages of ontogenesis, for example, in the larval stage, is called neoteny. Neotenia is characteristic, for example, of an amphibian animal - the Mexican ambistoma, which in natural conditions can remain in a larval state all its life. The larva lives in water, where it reproduces. This larva is called an axolotl, and it turns into an ambistome under the action of the thyroid hormone.

Kamenskiy A.A., Kriksunov E.V., Pasechnik V.V. Biology Grade 10
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Ontogenesis is called the set of processes occurring in the body, from the moment of formation of the zygote to death.

It is divided into two stages: embryonic and postembryonic.

The embryonic period The embryonic period is considered the period of embryonic development from the moment the zygote is formed to the release of the egg membranes or birth; in the process of embryonic development, the embryo goes through the stages of cleavage, gastrulation, primary organogenesis and further differentiation of organs and tissues. Crushed . Crushing is the process of formation of a multicellular single-layer embryo - blastula. Cleavage is characterized by: 1) cell division by mitosis with preservation of the diploid set of chromosomes; 2) a very short mitotic cycle; 3) blastomeres are not differentiated, and hereditary information is not used in them; 4) blastomeres do not grow and subsequently become smaller and smaller; 5) the cytoplasm of the zygote does not mix and does not move.

Development stages of the embryo.

1. The period of a single-celled embryo, or zygote, is short-term, flowing from the moment of fertilization to the beginning of egg cleavage. 2. Period of crushing. During this period, the cells multiply, the cells obtained during cleavage are called blastomeres. First, a bunch of blastomeres is formed, resembling a raspberry berry in shape - a morula, then a spherical single-layer blastula; blastula wall - blastoderm, cavity - blastocele. 3. Gastrulation. A single-layer embryo turns into a two-layer one - a gastrula, consisting of an external germ layer - an ectoderm and an internal one - an endoderm. In vertebrates, already in the course of gastrulation, a third germ layer, the mesoderm, arises. In the course of evolution in chordates, the process of gastrulation was complicated by the emergence of an axial complex of primordia (anlage of the nervous system, axial skeleton, and musculature) on the dorsal side of the embryo. 4. The period of isolation of the main rudiments of organs and tissues and their further development. Simultaneously with these processes, the unification of the parts into a single developing whole is intensified. From the ectoderm, the epithelium of the skin, the nervous system and partially the organs of the senses are formed, from the endoderm - the epithelium of the alimentary canal and its gland; from the mesoderm - muscles, the epithelium of the genitourinary system and serous membranes, from the mesenchyme - connective, cartilaginous and bone tissues, the vascular system and blood.

Consequences of the influence of alcohol, nicotine, narcotic substances on the human embryo.

The systematic use of drugs, which include alcohol, and even nicotine, causes damage to germ cells - sperm and eggs. A child may be born with a lag in length and body weight, poorly developing physically, predisposed to the development of any diseases. The stronger the narcotic substance used by the parents, the more serious the changes in the children's body can be. The use of these substances by women is especially dangerous.

2. Struggle for existence. The premise of natural selection. Forms of the struggle for existence.

Struggle for existence - complex and diverse relationships of individuals within a species, between species and with unfavorable conditions of inanimate nature. Charles Darwin points out that the discrepancy between the possibility of species for unlimited reproduction and limited resources is the main reason for the struggle for existence. The struggle for existence is of three types:

Intraspecific

Interspecific

Fight against abiotic factors