What is called personal development. Individual development of organisms - ontogenesis

2. Embryonic development of the embryo in animals:

a) crushing; crushing types;

b) gastrulation; methods of gastrulation;

c) primary organogenesis (laying of the axial complex of organs);

d) embryonic induction.

3. Postembryonic development:

a) post types embryonic development;

b) direct development - non-larval and intrauterine;

c) indirect development - with complete and incomplete metamorphosis.

4. Influence of environmental factors on the individual development of the organism.

1. Ontogenesis. Types of ontogeny. Periodization of ontogeny.

Ontogenesis - the process of individual development of an individual, i.e., the entire set of transformations from the moment the zygote is formed to the death of the organism.

In species that reproduce asexually, ontogenesis begins with the isolation of one or a group of cells of the mother's organism. In species with sexual reproduction, it begins with the fertilization of the egg. In prokaryotes and unicellular eukaryotic organisms, ontogeny is, in fact, a cell cycle, usually ending in cell division or cell death.

In the course of individual development, multicellular organisms undergo a number of regular processes:

The formation of morphofunctional features inherent in a particular biological species;

Implementation of specific functions;

Reaching puberty;

reproduction;

Aging;

All these processes, as components of ontogeny, proceed on the basis of hereditary information received by descendants from their parents. This information is a kind of instruction about the time, place and nature of the particular mechanisms of the development of the individual. Therefore, ontogeny can be defined as the process of implementing genetic information received from parents in certain environmental conditions.

There are the following types of ontogeny: direct and indirect. indirect development occurs in larval form, and direct development- in non-larval and intrauterine (Fig ...)

TYPES OF ONTOGENESIS

Direct development Indirect development

(with metamorphosis)

Non-larval type with incomplete metamorphosis:

(laying eggs with a large amount of yolk) egg - larva - adult - individual

Intrauterine with complete metamorphosis

Egg - larva - pupa - adult - individual

Ontogeny is a continuous process of development of an individual. However, its stages differ in content and mechanisms of ongoing processes. For this reason, the ontogeny of multicellular organisms is divided into periods: embryonic- from the moment of fertilization of the egg until the release of the egg membranes or the birth of the birth and postembryonic- from exit from the egg shells or birth to death. For placental animals and humans, the division into prenatal (before birth) and postnatal (after birth) periods is accepted. Often, a proembryonic, or prezygotic, period is also distinguished, including the processes of formation of germ cells (spermato- and ovogenesis).

1. Embryonic development in animals.

Embryonic (embryogenesis)) development begins from the moment the zygote is formed and is the process of transforming the latter into a multicellular organism.

Embryonic development consists of the following main stages:

splitting up, which results in the formation of a multicellular embryo;

gastrulation, during which the first tissues appear - ectoderm, endoderm And mesoderm, and the embryo becomes two- or three-layered;

primary organogenesis - the formation of a complex of axial organs of the embryo (neural tube, chord, intestinal tube);

exit from the egg or embryonic membranes (with larval and non-larval types of development) or birth (with intrauterine development).

Splitting up - the process of multiple rapidly successive mitotic divisions of the zygote, leading to the formation of a multicellular embryo. Cleavage divisions, unlike ordinary cell divisions, take place without a post-mitotic period, the resulting cells ( blastomeres) do not grow. During crushing, the total volume of the nucleus does not change, but

the size of its constituent cells decreases, i.e. the embryo is crushed.

The type of crushing of a fertilized egg depends on the amount of yolk and the nature of its distribution in the cytoplasm of the egg, that is, on the type of egg. In this regard, there is a distinction complete when the whole egg is crushed, and incomplete, when a part of it is crushed. This is due, in turn, to the fact that the yolk prevents the formation of a constriction during the division of the cell body.

Complete crushing is uniform, if the cells formed as a result of division are approximately the same in size, and uneven if they differ in size.

Incomplete crushing can be partial superficial, or discoidal.

Crushing happens synchronous(simultaneous division of all cells) and asynchronous(non-simultaneous cell division).

Isolecithal Moderatelecithal Telolecithal Alecithal

Complete, Complete, Incomplete, Complete,

Uniform Uneven Discoidal Uniform

(lancelet) (frog) (birds) asynchronous

(human)

Complete uniform crushing .

There is little yolk in the egg cell of the lancelet and it is evenly distributed in the cytoplasm, so the crushing of the fertilized egg is complete and uniform.

I - zygote; II, stages 2, 4, and 32 of blastomeres; III - blastula; IV - gastrula; V - laying of the axial complex of organs (1 - neural tube; 2 - chord; 3 - ectoderm; 4 - intestinal tube).

The 1st furrow runs in the meridional plane in the direction from the animal pole to the vegetative one; the zygote divides into two equal cells - blastomeres.

the 2nd furrow runs perpendicular to the first also in the meridional plane; 4 blastomeres are formed.

The 3rd sulcus is latitudinal - it runs slightly above the equator and immediately divides 4 blastomeres into 8 cells.

Further, the meridional and latitudinal furrows alternate correctly. As the number of cells increases, division becomes asynchronous. At the stage of 32 blastomeres, the embryo looks like a raspberry and is called morula. Blastomeres diverge further and further, forming a cavity at the stage of 64 blastomeres - blastocoel and the embryo takes the form of a bubble with a wall formed by one layer of cells closely adjacent to each other, inside which is primary body cavity, i.e. formed blastula (coeloblastula).

Complete uneven crushing.

Characteristic of moderately telolecithal eggs. In the egg of a frog, there is more yolk than in the lancelet, and it is concentrated mainly at the vegetative pole.

The first two meridional grooves divide the egg into 4 identical blastomeres.

3rd - the latitudinal furrow is strongly displaced towards the animal pole, where there is less yolk. As a result, 4 micro- and 4 macroblastomeres are formed, which differ sharply in size.

As a result of continued cleavage, the cells of the animal pole, which are less overloaded with yolk, divide more frequently and are smaller than the cells of the vegetative pole. The blastula has a wall formed by several rows of cells; the blastocoel is small and displaced towards the animal pole ( amphiblastula).

Incomplete discoidal cleavage.

Characteristic of telolecithal eggs of reptiles and birds, heavily overloaded with yolk. The yolk-free cytoplasm is about 1% of the volume. The yolk prevents cleavage and therefore only a narrow strip of cytoplasm at the animal pole is cleaved. As a result, a germinal disc (discoblastula)).

Regardless of the peculiarities of cleavage of fertilized eggs in different animals, due to differences in the amount and nature of the distribution of the yolk in the cytoplasm, cleavage, as a period of embryonic development, is characterized by the following features:

As a result of crushing, a multicellular embryo is formed (blastulation) - blastula and cellular material accumulates for further development.

All cells in the blastula have a diploid set of chromosomes (2n), are identical in structure and differ from each other mainly in the amount of yolk, i.e., blastula cells are not differentiated.

A characteristic feature of cleavage is a very short mitotic cycle compared to its duration in adult animals.

During the period of crushing, DNA and proteins are intensively synthesized, there is no RNA synthesis. The genetic information contained in the blastomere nuclei is not used.

During crushing, the cytoplasm does not move.

gastrulation - this is the process of formation of a two- or three-layer embryo - gastrula, which is based on complex and diverse movements of cell masses and cell differentiation. The resulting layers are called germ layers. They are layers of cells that have a similar structure, occupy a certain position in the embryo and give rise to certain organs and organ systems.

Distinguish between external ectoderm- and internal - endoderm- leaves, between which in three-layer animals is located mesoderm.

During gastrulation, cell division is either weakly expressed or absent - the embryo does not grow.

1 - invagination; 2 - epiboly; 3 - immigration; 4 - delamination.

Depending on the type of blastula, there are four main ways of gastrulation:

- intussusception– formation of a two-layer embryo by invagination of the blastula wall into the cavity of the blastocoel (lancelet);

- epiboly- the formation of a two-layer embryo as a result of the creeping of small cells of the animal pole onto the vegetative one, the cells of the animal pole overgrow it and it is inside the embryo (amphibian);

- immigration– penetration by immersion of part of the blastula cells into the blastocoel (coelenterates);

- delamination- as a result of cell division, the germinal disk, as it were, splits into two layers (reptiles and birds).

However, in its pure form, the listed methods of gastrulation are almost never found in nature, which gives reason to single out the fifth method - mixed, or combined.

gastrula is a two-layer bag, the cavity of which (gastrocoel) communicates with the external environment through a hole - blastopore(primary mouth). The outer layer of the gastrula is the ectoderm, the inner layer is the endoderm. The structure of the gastrula depends on the type of egg and the lifestyle of the embryo at this stage. So, in intestinal cavities, the gastrula is a free-living larva - planula, in other species, the gastrula develops in the egg membranes or in the mother's body.

In some animals (sponges, coelenterates), the gastrulation process ends with the formation of two germ layers - ecto- and endoderm. For other representatives of the animal world, the stage of formation of the third germ layer, the mesoderm, is characteristic. The laying and formation of the mesoderm is carried out in two ways: teloblastic And enterocoelous. With the teloblastic method of laying in the area of ​​​​the lips of the blastopore, 2 large cells stand out ( teloblasts); multiplying, they give rise to two mesodermal stripes, from which (with the appearance inside the cavity) coelomic vesicles are formed. With the enterocoel method of laying, the primary intestine forms symmetrical protrusions into the blastocoel, which then lace off and turn into coelomic vesicles. In both cases, the anlage bubbles grow and fill the primary body cavity. The layer of mesoderm adjacent to the ectoderm is called parietal, or parietal leaf, and adjacent to the endoderm - visceral, or visceral leaf. The cavity formed in the mesoderm vesicles and replacing the primary one is called secondary body cavity, or whole. With the teloblastic method of laying the mesoderm, the blastopore turns into the mouth of an adult animal ( protostomes). With the enterocoel method, the blastopore closes, and the mouth of an adult is formed a second time ( deuterostomes).

The formation of germ layers is the result of differentiation of relatively homogeneous blastula cells similar to each other.

Differentiation - this is the process of the appearance and growth of morphological and functional differences between individual cells and parts of the embryo.

Morphological differentiation manifests itself in the formation of several hundred types of cells of a specific structure.

Biochemical differentiation- specialization of cells in the synthesis of specific proteins characteristic only of this cell type. Keratin is synthesized in the epidermis, insulin is synthesized in the islet tissue of the pancreas, etc. The biochemical specialization of cells is ensured by the differential activity of genes, i.e., different genes begin to function in different primordia. Genetic information is realized through the synthesis of mRNA at the gastrula stage, which increases sharply during the formation of the axial complex of organs.

With further differentiation of cells of the germ layers in the process of histo- and organogenesis, the same tissues and organs are formed in different animal species, which means that the germ layers are homologous. The homology of the germ layers of the vast majority of animals is one of the proofs of the unity of the animal world.

Histo- and organogenesis.

After completion of gastrulation, a complex of axial organs is formed in the embryo: the neural tube, chord and intestinal tube. Consider this process using the example of a lancelet

The ectoderm, located on the dorsal side of the embryo, bends along the midline, forming a longitudinal groove. The sections of ectoderm located to the right and left of the groove begin to grow on its edges. The groove - the rudiment of the nervous system - plunges under the ectoderm and its edges close (the process is called neurulation, and the stage of development is neurula). The neural tube is formed. The rest of the ectoderm is the rudiments of the skin epithelium, sensory organs.

The dorsal part of the endoderm, located under the neural tube, gradually separates (separates) from the rest of the endoderm and folds into a dense elastic cord - chord. From the rest of the endoderm, the intestinal epithelium, digestive glands, and respiratory organs develop.

Further differentiation of germ cells leads to the emergence of numerous derivative germ layers - organs and tissues.

embryonic induction.

The process of cell differentiation is largely due to the influence of the parts of the developing embryo on each other. Observations of the development of a fertilized frog ovum make it possible to trace the path of development of cells in different parts of the embryo. It turns out that strictly defined cells occupying a strictly defined place in the blastula give rise to strictly defined rudiments of organs. With the onset of gastrulation, the movement of cells begins. If at this moment (at the early gastrula stage) a part of the cells on the dorsal side is cut out - the rudiment of the axial complex and transplanted under the skin ectoderm of another embryo on the ventral side, then an additional complex of axial organs can be developed in the second embryo. In this case, the embryo, which has lost its organizer cells, dies. Consequently, in the process of development, one germ influences the other, determining the path of its development. Such a phenomenon is called embryonic induction, and the parts of the embryo that guide the development of structures associated with them are called inductors(or organizational centers). The phenomenon of induction is also observed in the appearance of other organs: the contact of the protrusion of the neural tube - the eye bubble - with the ectoderm leads to the development of the lens of the eye; the lens, in turn, induces the transformation of the ectoderm into the cornea.

Unfavorable environmental factors in which the future organism is formed (temperature, light, humidity, alcohol, nicotine, pesticides, a number of medicines, drugs, etc.). They can disrupt the normal course of embryogenesis and lead to the formation of various deformities or a complete stop of development.

Derivatives of the germ layers

ECTODERM	ENDODERMA	MESODERM
Neural plate, giving rise to the central and peripheral nervous system; Ganglionic plate, from which ganglia of the autonomic nervous system, cells of the adrenal medulla, pigment cells are formed; Components of the organs of vision, hearing, smell; The epidermis of the skin, hair, nails, sweat, sebaceous and mammary glands; Tooth enamel; Epithelium of the oral cavity and rectum.	Epithelium of the intestinal tube (midgut); Liver, pancreas; Lungs; Gill epithelium.	All types of connective tissue (bones, cartilage, tendons, dermis); Skeletal muscles; Circulatory system; excretory system; Sexual system.

The concept of individual development

In modern biology, there are several categories related to development. We know that the process of continuous development of living nature is called biological evolution.

Definition 1

The successive stages in the development of all forms of the organic world from the lowest to the highest are called phylogenetic development or phylogeny.

But there is also the concept of individual development of organisms. It begins from the moment of fertilization of the egg and is completed by the cessation of the vital processes of the organism as a result of its death.

Definition 2

Ontogenesis is the individual development of an organism from its inception to death.

In different groups of organisms, ontogeny has its own characteristics. In unicellular organisms, the process of individual development coincides with the cell cycle. The duration of ontogeny can also differ significantly in different groups of living organisms. Some plants (for example, sequoia) can live for more than $3,000 years, other organisms can survive for several hours.

Studying the individual development of organisms, scientists noticed that in the course of ontogenesis, the organism goes through the stages of development of the organic world. The famous phylogenetic law states that ontogeny is a brief repetition of phylogeny. This is an eloquent confirmation of evolutionary theory.

Beginning of ontogeny

The question of the beginning of the development of an organism concerns not only biology, but also philosophy. With vegetative propagation, in general, you can say. That the organism continues to exist only in a slightly different form (after all, the genotype has been completely preserved).

Therefore, today in biology it is customary to consider the beginning of ontogenesis during vegetative reproduction the beginning of differentiation of cells and organs of a multicellular primordium (body fragment, kidney, etc.) and growth. In the case of reproduction by spores (fungi, bacteria, algae, spore plants), the spore is a single cell, which then quickly divides into many daughter cells. Newly formed cells differentiate. Therefore, the dispute can be a starting point of reference.

In sexual reproduction, the initial stage of ontogenesis is the formation of a zygote - a fertilized egg. In the case of parthenogenesis, the beginning of the development of an unfertilized egg is taken as the initial stage.

Stages of individual development

Individual development is a complex process. Each type of organism has its own characteristics. In general, most scientists conditionally divide the process of ontogenesis into two important stages:

1. embryogenesis,
2. postembryogenesis.

Each of these stages has its own characteristics and is also divided into certain stages.

Definition 3

Embryogenesis (embryonic development) - this is the period of development of a living organism from the moment of the fusion of gametes and the formation of a zygote and until the birth or hatching of the organism (seed germination in plants).

Some scientists believe that postembryonic development should be considered as the period from the birth of an organism to the acquisition of its ability to reproduce.

Due to the ambiguity of points of view, the postembryonic period is often divided into age stages. For example, in the postembryonic development of a person, childhood, youth, maturity, and old age are distinguished. Each stage is characterized by features of physical development, physiological and mental processes in the body, their intensity.

The postembryonic development of living organisms is studied by specialists from various disciplines. The issues of age-related changes in the human body are studied by the science of gerontology.

Remember!

What periods make up the individual development of the organism?

What is development with metamorphosis?

The indirect, or larval, type of development is characteristic of many invertebrates and some vertebrates (fish and amphibians). This implies the birth of an individual, sometimes completely unlike an adult organism. In the process of indirect development, an individual passes through one or more larval stages (a tadpole in a frog, a caterpillar in a butterfly). The larvae lead an independent life, actively feed, grow and develop. After a certain time, the larva turns into an adult - metamorphosis occurs, therefore this type of development is sometimes called development with metamorphosis. During metamorphosis, the larval organs are destroyed and there are organs inherent in adult animals. For many species, the presence of a larval stage in the development process is the possibility of settling and the absence of competition between individuals of different ages for habitat and food.

What organisms are characterized by this type of development?

Fish, amphibians, some insects

Review questions and assignments

1. What is called the individual development of the organism? Give a definition of this concept.

The individual development of an individual, the totality of its transformations from its inception to the end of life, is called ontogeny.

2. List the periods of ontogeny.

In organisms that reproduce sexually, individual development begins from the moment of fertilization and the formation of a zygote and is divided into two periods: embryonic (the period of embryonic development) and postembryonic (the period of post-embryonic development). The ratio of the duration of these periods in organisms of different species can vary greatly.

3. What development is called embryonic, and what is postembryonic?

Embryonic period (embryogenesis). This period lasts from the moment of formation of the zygote to the release of the embryo from the egg or birth. It proceeds in several stages. postembryonic period. This period begins with the birth of the organism and ends with its death. There are indirect and direct types of postembryonic development.

4. What are the types of postembryonic development of an organism? Give examples.

The indirect, or larval, type of development is characteristic of many invertebrates and some vertebrates (fish and amphibians). This implies the birth of an individual, sometimes completely unlike an adult organism. In the process of indirect development, an individual passes through one or more larval stages (a tadpole in a frog, a caterpillar in a butterfly). Direct development - this type of development is typical for organisms whose cubs are born already similar to adults. Direct development is oviparous or intrauterine.

5. What is the biological significance of metamorphosis?

After a certain time, the larva turns into an adult - metamorphosis occurs, therefore this type of development is sometimes called development with metamorphosis. During metamorphosis, the larval organs are destroyed and there are organs inherent in adult animals. For many species, the presence of a larval stage in the development process is the possibility of settling and the absence of competition between individuals of different ages for habitat and food, since larvae and adults can live in different environments and have different types of food.

Germinal sheets (embryonic layers, lat. folia embryonalia) - layers of the body of the embryo of multicellular animals, formed during gastrulation and giving rise to various organs and tissues.

7. What is cell differentiation? What do you think can cause disruption of cell differentiation during development?

Differentiation is the process of transformation of unspecialized germ cells into various cells of the body that differ in structure and perform certain functions. Differentiation does not begin immediately, but at a certain stage of development and is carried out through the interaction of the germ layers (at an early stage) and the rudiments of organs (at a later stage). Differentiation of embryonic cells does not occur immediately, but at a certain stage of development. In the early stages of fragmentation, the cells of the embryo are not yet specialized, so each of them can give rise to a whole organism. If for any reason these cells separate, two identical embryos are formed, containing identical genetic information, each of which develops into a full-fledged individual. As a result, identical, or monozygotic, twins are born. In the human population, these are the only people who have an identical genotype and are copies of each other. Yes, differentiation disorders can occur at any stage of embryogenesis, for various reasons.

8. Describe the concept of "growth". What is a certain growth; indefinite growth? What type of growth is typical for plant organisms?

Growth - an increase in the mass and linear dimensions of an individual due to an increase in the number and size of cells and non-cellular formations. With the type of growth that is called definite, the organism, having reached a certain level of maturity, ceases to grow in size. Most animals, growing up, grow more and more slowly and, having reached a certain age, stop growing. This type of growth is called definite. This type of growth is typical for most animals. If the organism grows throughout its life, then they speak of an indefinite type of growth. It is characteristic of plants, fish, molluscs, amphibians. With an indeterminate type of growth, organisms grow throughout their lives, such as molluscs, fish and amphibians. After the completion of active growth, the body enters the stage of maturity, which is associated with childbearing. The process of individual development ends with aging and death. Plant organisms are characterized by unlimited growth - an indefinite type.

Think! Remember!

1. Why do different tissues and organs form from germ cells that are equivalent at the beginning of development?

Differentiation does not begin immediately, but at a certain stage of development and is carried out through the interaction of germ layers (at an early stage) and rudiments of organs (at a later stage). Differentiation of embryonic cells does not occur immediately, but at a certain stage of development. In the early stages of fragmentation, the cells of the embryo are not yet specialized, so each of them can give rise to a whole organism. If for any reason these cells separate, two identical embryos are formed, containing identical genetic information, each of which develops into a full-fledged individual.

2. Do you know the types of organisms whose period of embryonic development is longer than the postembryonic period? If yes, please explain what these features are related to.

3. How do you understand the following statement: “Derivatives of several germ layers take part in the construction of any organ or part of the body”? Give examples to prove this statement.

An organism or an organ cannot be built from one leaf; for this, all three leaves are needed, since each of them is responsible for the formation of specific tissues. For example, the epithelium of the skin is formed by the ectoderm, and the epithelium of the intestine by the endoderm.

4. Recall from previous biology courses how the development of egg-laying mammals (subclass Primal Beasts) and representatives of the infraclass Lower animals (order Marsupials) differ from the development of other mammals (infraclass Higher animals).

Question 1. What is called the individual development of the organism?
The individual development of an organism or ontogenesis is the whole set of transformations of an individual from its inception to the end of life. In the cell, from which ontogenesis begins, the program of the development of the organism is laid down. It is implemented through the interaction of the nucleus (genetic information) and the cytoplasm of each cell, as well as cells and tissues with each other.
In bacteria and unicellular eukaryotes, ontogenesis begins at the moment of formation of a new cell as a result of division and ends with death or a new division.
In multicellular organisms that reproduce asexually, ontogeny begins from the moment of isolation of a cell or group of cells of the mother organism.
In organisms that reproduce sexually, ontogenesis begins from the moment of fertilization and the appearance of a zygote.

Question 2. List the periods of ontogeny.
Periods of ontogeny:
In ontogenesis, 3 periods are distinguished: proembryonic, embryonic And postembryonic. For higher animals and humans, the division into prenatal (before birth), intranatal (birth) and postnatal (after birth) periods of development is accepted.
pre-embryonic period . pre-embryonic period, preceding the formation of a zygote, is associated with the formation of gametes. Otherwise, it is gametogenesis (ovogenesis and spermatogenesis).
Embryonic period . Embryonic period(Greek embryon - embryo) begins with fertilization and the formation of a zygote. The end of this period in different types of ontogeny is associated with different moments of development. The embryonic period is divided into the following stages:
1) fertilization - the formation of a zygote;
2) crushing - the formation of blastula;
3) gastrulation - the formation of germ layers;
4) histo- and organogenesis - the formation of organs and tissues of the embryo. Postembryonic period of animal development.
Postembryonic period The development of animals begins after their birth is divided into three periods:
The period of growth and shaping (pre-reproductive);
Maturity period (reproductive);
The period of old age (post-reproductive).
Postembryonic period human development.
Postembryonic postnatal) period of human development, otherwise called postnatal is also divided into three periods:
1) Juvenile (before puberty);
2) Mature (adults, sexually mature state);
3) A period of 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.

Question 3. What development is called embryonic, and what - postembryonic?
Ontogeny is divided into two periods. The first of them - the embryonic period (embryogenesis) lasts from the moment of fertilization until the release from the egg or birth. Let us describe its stages using the example of a lancelet.
Cleavage: the egg divides many times and quickly by mitosis, the interphases are very short;
blastula: a hollow ball is formed, consisting of a single layer of cells; at one of the poles of the ball, cells begin to divide more actively, preparing the next stage;
gastrula: formed as a result of invagination of the more actively dividing blastula pole; early gastrula is a two-layer embryo; its outer layer (germ layer) is called the ectoderm, the inner layer is the endoderm; the gastrula cavity is the future intestinal cavity of the body; late gastrula - a three-layer embryo: it is formed in all organisms (except intestinal and sponges) when the third germ layer is laid - the mesoderm, which occurs between the ectoderm and endoderm;
histo- and organogenesis: the development of tissues and organ systems of the embryo occurs. The second stage of ontogeny is the postembryonic period. It lasts from the moment of exit from the egg (or birth) until death.

Question 4. What are the types of postembryonic development of the organism? Give examples.
There are two types of postembryonic development.
Indirect development, or development with metamorphosis. This type of development is characterized by the fact that the born individual (larva) often does not look like an adult organism at all. After some time, she undergoes metamorphosis - the transformation into an adult form. Indirect development is inherent in amphibians, insects and many other organisms.
direct development. With this type of development, the born calf is similar to an adult. Direct development is oviparous and intrauterine. During oviparous development, the embryo spends the first stage of ontogenesis in an egg supplied with nutrients and protected by a shell (shell) from environment. This is how, for example, the young of birds, reptiles and egg-laying mammals develop. During intrauterine development, the growth of the embryo occurs inside the mother's body. All vital functions (nutrition, respiration, excretion, etc.) are carried out by interacting with the mother through a special organ - the placenta, formed by the tissues of the uterus and the embryonic membranes of the cub. The intrauterine type of development is characteristic of all higher mammals, including humans.

Question 5. What is the biological significance of metamorphosis?
Metamorphosis makes it possible for individuals of different ages not to compete for food. For example, tadpoles and frogs, butterflies and caterpillars have different food sources. Also, the presence of a larval stage often increases the possibility of dispersal of organisms. This is especially important if adults are sedentary (eg many marine molluscs, worms and arthropods).

Question 6. Tell us about the germ layers.
The first two germ layers - ectoderm and endoderm are laid at the stage of formation of the gastrula from the blastula. Later, in all (except intestinal and sponges), the third germinal layer develops - the mesoderm, which is located between the ectoderm and endoderm. Further, all organs of the embryo develop from three germ layers. For example, in humans, the nervous system, skin glands, tooth enamel, hair, nails, and outer epithelium are formed from the ectoderm. From the endoderm - tissues lining the intestines and respiratory tract, lungs, liver, pancreas. Muscles, cartilage and bone skeleton, organs of the excretory, endocrine, reproductive and circulatory systems are formed from the mesoderm.

Question 7. What is cell differentiation? How is it carried out in the process of embryonic development?
Differentiation- this is the process of transformation of non-specialized germ cells into various cells of the body, differing in structure and performing certain functions. Differentiation does not begin immediately, but at a certain stage of development and is carried out through the interaction of the germ layers (at an early stage) and the rudiments of organs (at a later stage).
Some cells, even in an adult organism, remain incompletely differentiated. Such cells are called stem cells. In humans, they are found, for example, in the red bone marrow. Currently, the possibility of using stem cells to treat many diseases, restore organs after injuries, etc. is being actively explored.

Question 8. Describe the concept of "growth". What is a certain height? Indefinite growth?
The growth of the body is accompanied by an increase in cells and the accumulation of body weight. Distinguish between definite and indefinite growth.
Indefinite growth is characteristic of mollusks, crustaceans, fish, amphibians, reptiles and other animals that do not stop growing throughout their lives.
Certain growth is characteristic of organisms that grow only for a limited lifetime, such as insects, birds, and mammals. In humans, intensive growth stops at the age of 13-15 years, corresponding to the period of puberty.
The growth and development of the organism is controlled genetically, and also depends on the conditions of the environment in which development takes place.
With the type of growth that is called definite, the organism, having reached a certain level of maturity, ceases to grow in size. This type of growth is typical for most animals. If the organism grows throughout its life, then they speak of an indefinite type of growth. It is characteristic of plants, fish, molluscs, amphibians.

Remember!

What periods make up the individual development of the organism?

What is development with metamorphosis?

What organisms are characterized by this type of development?

Individual development of an individual, the totality of its transformations from the beginning to the end of life called ontogeny. According to modern scientific ideas, in the cell from which the ontogeny of an individual begins, a certain program for the further development of the organism is laid down. In the process of ontogenesis, this hereditary program is implemented through the interaction of the nucleus and cytoplasm of each cell, individual cells with each other and tissues with each other. As a result of these complex relationships, based on the available genetic information and depending on external conditions, a specific individuality of an individual is formed.

In bacteria and unicellular eukaryotic organisms, ontogenesis begins at the moment of formation of the organism as a result of the division of the mother cell and ends either with the death of the cell or with the next division of the organism, i.e., in fact, coincides with the cell cycle.

In multicellular organisms that reproduce asexually, ontogenesis begins with the isolation of one or more cells of the mother organism, giving rise to a new individual.

In organisms that reproduce sexually, individual development begins from the moment of fertilization and the formation of a zygote and is divided into two periods: embryonic (the period of embryonic development) and postembryonic (the period of post-embryonic development). The ratio of the duration of these periods in organisms of different species can vary greatly.

Embryonic period (embryogenesis). This period lasts from the moment of formation of the zygote to the release of the embryo from the egg or birth. It proceeds in several stages (Fig. 62). In the first stage, which is called crushing, the fertilized egg divides by mitosis, resulting in 2, 4, 8, 16, etc. cells that fit tightly together. The interphase between divisions is very short, the cells do not grow, so the crushing process occurs very quickly. Crushing ends with the formation blastula- a hollow ball, the wall of which consists of a single layer of cells. Further, at one of the blastula poles, the cells begin to divide more actively and go deep into the spherical embryo, forming an invagination. As a result of this process, a two-layer embryo is formed - gastrula. The two layers of cells that form its walls are called germ layers: outer sheet - ectoderm and internal - endoderm.

In all animals, except for sponges and coelenterates, with the further development of the embryo, a third germ layer is formed between the ectoderm and endoderm - mesoderm.

Further development of the embryo is associated with the interaction of three germ layers, from which all tissues and organs of the body are formed. The development of organ systems of the embryo - organogenesis- occurs in a certain sequence. In chordates, it begins with the formation of the rudiment of the notochord and the nervous system. On the dorsal side of the embryo, a group of ectoderm cells separates in the form of a long plate. These cells begin to actively divide, plunging into the body of the embryo and forming a groove, the edges of which gradually approach and then close, forming the primary neural tube.

Rice. 62. Cleavage of a fertilized lancelet egg and the formation of germ layers

In addition to the nervous system, skin glands, tooth enamel, hair, nails, and skin epithelium also arise from the ectoderm. Endoderm gives rise to tissues lining the intestines and respiratory tract, forms the liver and pancreas. Muscles, cartilage and bone skeleton, organs of the excretory, reproductive and circulatory systems of the body are formed from the mesoderm.

In the process of embryogenesis, there is a close interaction between the parts of the developing embryo: the rudiment of one organ or organ system determines (induces) the location and time of formation of another organ or organ system.

The mutual influence of parts of the embryo has been demonstrated in numerous experiments. The German researchers Hans Spemann and Hild Mangold took a portion of the dorsal side of the body from a newt embryo at the early gastrula stage, from which the notochord and mesoderm were to develop later, and transplanted it onto the ventral side of another gastrula. As a result, on the ventral side of the second embryo, an additional neural tube was formed from the cells that were supposed to give rise to the skin. This phenomenon has been named embryonic induction.

Differentiation of embryonic cells does not occur immediately, but at a certain stage of development. In the early stages of fragmentation, the cells of the embryo are not yet specialized, so each of them can give rise to a whole organism. If for any reason these cells separate, two identical embryos are formed, containing identical genetic information, each of which develops into a full-fledged individual. As a result, identical or monozygotic twins are born. In the human population, these are the only people who have an identical genotype and are copies of each other.

In some animals, the embryo at an early stage of development is divided into several fragments. At the same time, each of the formed fragments gives rise to a full-fledged organism. As a result, all cubs of one generation turn out to be absolute copies of each other. This type of reproduction is typical for armadillos. Therefore, in the litter of the nine-banded armadillo tattoo there is always an even number of same-sex cubs.

postembryonic period. This period begins with the birth of the organism and ends with its death.

There are indirect and direct types of postembryonic development.

Indirect development. The indirect, or larval, type of development is characteristic of many invertebrates and some vertebrates (fish and amphibians). This implies the birth of an individual, sometimes completely unlike an adult organism. In the process of indirect development, an individual passes through one or more larval stages (a tadpole in a frog, a caterpillar in a butterfly) (Fig. 63). The larvae lead an independent life, actively feed, grow and develop. After a certain time, the larva turns into an adult - occurs metamorphosis, so sometimes this type of development is called development with metamorphosis. During metamorphosis, the larval organs are destroyed and there are organs inherent in adult animals.

For many species, the presence of a larval stage in the process of development is the possibility of settling and the absence of competition between individuals of different ages for habitat and food.

direct development. This type of development is characteristic of organisms whose young are born already similar to adults. A newly hatched duckling, a born puppy or a child of a person differs from an adult in smaller sizes, slightly different body proportions and underdevelopment of some organ systems, for example, the sexual one. Direct development is oviparous or intrauterine.

Rice. 63. Sequential stages of metamorphosis in a frog (from bottom to top): tadpoles in eggs, the beginning of metamorphosis, a frog with the remains of a tail

non-larval, or oviparous, the type of development is characteristic of reptiles, birds, egg-laying mammals, and a number of invertebrates. The eggs of these organisms are rich in nutrients (yolk), and the embryo can develop inside the egg for a long time.

intrauterine the type of development is characteristic of all higher mammals, including humans. All vital functions of the embryo in this type of development are carried out through interaction with the mother's body through a special organ - the placenta.

Embryonic development ends with the birth process. After birth, an active growth of the organism is usually observed, i.e., an increase in its size and mass. Most animals, growing up, grow more and more slowly and, having reached a certain age, stop growing. This type of growth is called certain. At uncertain type of growth organisms grow throughout their lives, such as mollusks, fish and amphibians. After the completion of active growth, the body enters the stage of maturity, which is associated with childbearing. The process of individual development ends with aging and death.

Review questions and assignments

1. What is called the individual development of the organism?

2. List the periods of ontogeny.

3. What development is called embryonic, and what is postembryonic?

4. What are the types of postembryonic development of an organism? Give examples.

5. What is the biological significance of metamorphosis?

6. Tell us about the germ layers.

7. What is cell differentiation? How is it carried out in the process of embryonic development?

8. Describe the concept of "growth". What is a certain height? Indefinite growth?

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