The animal organism develops for a certain time in the mother's body or in the egg. Therefore, we can observe the development of animals only from the moment of their birth. Calves or foals are born sighted, covered with wool, a few hours after birth they can walk on their own. They are very cute and look like their parents. (Fig. 45). For some time, the animals feed on mother's milk, after which they begin to consume food on their own. With age, their body becomes larger, but they will be adults (mature) only after a few years.
A chick that has just hatched from an egg is covered with fluff and after a few hours begins to run and feed on its own. He will become an adult in a year.
The development in which a newborn organism resembles an adult animal is called direct .
Otherwise, butterflies, beetles or frogs develop. Egg hatches Living being not at all like their parents. From the moment of birth until the appearance of signs of an adult animal, complex transformations take place with it. Let's consider this on the example of a rather common cabbage white butterfly in Ukraine. (Fig. 46).
First, an adult female lays eggs on plants. Each egg hatches into a larva called caterpillar . She actively eats the leaves of plants, especially likes cabbage leaves and can completely eat them, leaving only the veins. The caterpillar grows rapidly, increasing in size, so it has to molt several times - shed too tight cover. Time passes and the caterpillar-glutton stops eating and turns into a motionless caterpillar. chrysalis . At first glance, the chrysalis appears lifeless. In fact, changes are taking place inside it that culminate in the formation of an adult butterfly. After the chrysalis opens, the butterfly spreads its wings, which quickly dry out, and takes off into the sky. An adult butterfly feeds on the nectar of flowers, while contributing to the cross-pollination of plants.
Both the caterpillar and the chrysalis are not at all like a butterfly. This development of animals is called indirect . material from the site
In frogs, indirect development begins with the appearance of a tadpole from the spawn ( rice. 17). He also does not look like an adult animal. The tadpole breathes with gills and lives only in water. At first, he has no limbs at all, but there is a tail, with the help of which he moves. Over time, the hind limbs appear, then the front ones grow. The tail is shortened and disappears completely by the time the animal leaves the land. Instead of gills, lungs are formed, which the animal breathes on land.
Growth and development are peculiar only to living beings. This distinguishes them from inanimate nature.
1. Direct development - development in which the emerging organism is identical in structure to an adult organism, but is smaller and does not have sexual maturity. Further development is associated with an increase in size and the acquisition of puberty. For example: the development of reptiles, birds, mammals.
2. Indirect development (larval development, 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 accompanied by growth.
Ticket number 26. The biosocial nature of man as a reflection of the evolutionarily conditioned hierarchy of living nature. The value of human biological heritage in modern conditions life.
On the planet, among other creatures, people have a unique place, which is due to the acquisition by them in the process of anthropogenesis of a special quality - social essence. This means that it is no longer biological mechanisms, but primarily the social structure, intellect, production, labor that ensure survival, global and even space settlement, and the well-being of mankind. Sociality, however, does not oppose people to the rest of living nature. The person stays logged in organic world. This world took shape and developed throughout most of the history of the planet, regardless of the human factor, moreover, at a certain stage of its development, it gave rise to this factor. Mankind is a peculiar but integral component of the biosphere. A prominent domestic pathologist I.V. Davydovsky wrote that the naturalness and legitimacy of diseases follow from the basic properties of life, namely from the universal and the most important property organisms to adapt to changing environmental conditions. In his opinion, the fullness of such adaptation is the fullness of health.
Ticket number 27 Gametogenesis or pre-embryonic development is the process of maturation of germ cells, or gametes. Since during gametogenesis the specialization of eggs and sperm occurs in different directions, oogenesis and spermatogenesis are usually distinguished, respectively. Gametogenesis is naturally present in life cycle a number of protozoa, algae, fungi, spore and gymnosperms, as well as multicellular animals. In some groups, gametes are secondarily reduced (marsupials and basidiomycetes, flowering plants). The processes of gametogenesis have been studied in most detail in multicellular animals.
Gametogenesis
(from gametes and Greek genesis - origin), the process of development and formation of germ cells - gametes. G. male gametes (spermatozoa, spermatozoa) are called spermatogenesis, female gametes (eggs) - oogenesis. G. proceeds differently in animals and plants, depending on the place of meiosis in the life cycle of these organisms.
In multicellular animals, G. occurs in special organs - the sex glands, or gonads (ovaries, testes, hermaphroditic sex glands), and consists of three main stages: 1) reproduction of primary germ cells - gametogonia (spermatogonia and oogonia) through a series of successive mitoses, 2) the growth and maturation of these cells are now called gametocytes (spermatocytes and oocytes), which, like gametogonia, have complete ( for the most part diploid) set of chromosomes. At this time, the main event of G. occurs in animals - the division of gametocytes by meiosis, leading to a reduction (halving) in the number of chromosomes in these cells and their transformation into haploid cells (see Haploid) - spermatids and ootids; 3) the formation of sperm (or sperm) and eggs; in this case, the eggs are dressed next to the embryonic membranes, and the spermatozoa acquire flagella, which ensure their mobility. In females of many animal species, meiosis and egg formation are completed after the penetration of the spermatozoon into the cytoplasm of the oocyte, but before the fusion of the nuclei of the spermatozoon and the egg.
In plants, G. is separated from meiosis and begins in haploid cells - in spores (in higher plants - microspores and megaspores). The sexual generation of the plant develops from the spores - the haploid gametophyte, in the genital organs of which - the gametangia (male - antheridia, female - archegonia) G occurs by mitosis. The exception is gymnosperms and angiosperms, in which spermatogenesis occurs directly in the germinating microspore - pollen cell. In all lower and higher spore-bearing plants, G. in antheridia is a multiple division of cells, as a result of which a large number of small motile spermatozoa are formed. G. in archegonia - the formation of one, two or more eggs. In gymnosperms and angiosperms, male G. consists of division (by mitosis) of the nucleus of the pollen cell into generative and vegetative, and further division (also by mitosis) of the generative nucleus into two spermatozoa. This division occurs in the germinating pollen tube. Female G. in angiosperms - isolation by mitosis of one egg inside the 8-nuclear embryo sac. The main difference between G. in animals and plants: in animals, it combines the transformation of cells from diploid to haploid and the formation of haploid gametes; G. in plants is reduced to the formation of gametes from haploid cells.
Gametes (from Greek ?????? - wife, ??????? - husband) are reproductive cells that have a haploid (single) set of chromosomes and are involved in gamete, in particular, sexual reproduction. When two gametes merge in the sexual process, a zygote is formed, which develops into an individual (or group of individuals) with the hereditary characteristics of both parental organisms that produced gametes.
In some species, the development of a single gamete (an unfertilized egg) into the body is also possible - parthenogenesis.
Morphology of gametes and types of gametogamy
Morphology of gametes various kinds is quite diverse, while the produced gametes can differ both in the chromosome set (with the heterogamety of the species), size and mobility (the ability to move independently), while gamete dimorphism in different species varies widely - from the absence of dimorphism in the form of isogamy to its extreme manifestations in the form of oogamy.
isogamy
If the merging gametes do not morphologically differ from each other in size, structure and chromosome set, then they are called isogametes, or asexual gametes. Such gametes are motile, may carry flagella or be amoeboid. Isogamy is typical of many algae.
Anisogamy (heterogamy)
Gametes capable of fusion differ in size, mobile microgametes carry flagella, macrogametes can be both mobile (many algae) and immobile (macrogametes devoid of flagella of many protists).
The gametes of one biological species capable of fusion sharply differ in size and mobility into two types: small mobile male gametes - spermatozoa - and large immobile female gametes - eggs. The difference in the size of the gametes is due to the fact that the eggs contain a supply of nutrients sufficient to provide the first few divisions of the zygote during its development into an embryo.
Male gametes - spermatozoa - of animals and many plants are motile and usually carry one or more flagella, with the exception of the male gametes of seed plants - sperm, which are delivered to the egg during germination of the pollen tube, as well as flagellaless spermatozoa (sperms) of nematodes and arthropods.
Although sperm cells carry mitochondria, in oogamy only nuclear DNA passes from the male gamete to the zygote, mitochondrial DNA (and in the case of plants, plastid DNA) is usually inherited by the zygote only from the egg.
Ticket number 28. Unconventional inheritance (genomic imprinting, uniparental disomy, expansion of trinucleotide repeats, mitochondrial inheritance).
EXPANSION OF TRINUCLEOTIDE FRAGMENTS - a pathological condition: a variant of a genetic mutation characterized by the appearance in DNA of "meaningless" repeats of trinucleotides, which can lead to disorganization of the functioning of DNA or the synthesis of a pathological protein that accumulates in cells, which leads to cell death. Underlies a number of diseases (Huntington's disease, Kennedy's disease, spinocerebellar degeneration, etc.), the severity of which depends on the number of trinucleotide repeats. General feature This group of diseases is an earlier onset and an increase in the severity of their clinical manifestations from generation to generation, which usually reflects an increase in the number of trinucleotide repeats (anticipation phenomenon). Recently, another type of inheritance has been highlighted - mitochondrial. Mitochondria are transferred with the cytoplasm of the eggs. Sperm do not have mitochondria, since the cytoplasm is eliminated during the maturation of male germ cells. An egg contains about 25,000 mitochondria. Each mitochondrion contains a circular chromosome. Gene mutations in mitochondrial DNA found in Leberaf optic nerve atrophy, mitochondrial myopathies, progressive ophthalmoplegia. Diseases caused by this type of heredity are transmitted from mother to daughters and sons equally. Sick fathers do not transmit the disease to their daughters or sons.
Genomic imprinting is an epigenetic process in which the expression of certain genes is carried out depending on which parent the gene allele came from. This is a non-inherited process that is not subject to Mendelian inheritance. Gene imprinting causes the expression of alleles of a gene derived from the mother in the case of the H19 or CDKN1C genes and from the father in the case of the IGF2 gene. Imprinting of some genes within the genome has been shown for insects, mammals, and flowering plants.
Gene imprinting is carried out using the process of DNA methylation. If, for some reason, imprinting does not work, this can lead to the appearance genetic disorders(e.g. Prader-Willi Syndrome).
Uniparental disomy, that is, the inheritance of both copies of the whole chromosome or part of it from one parent (in the absence of the corresponding genetic material from the other parent), is an exception to the Mendelian principles of inheritance. It is rare and causes, for example, Prader-Willi syndrome and Angelman syndrome.
The role of disomy in pathology is greatly exacerbated by genomic imprinting, which leads to unequal expression of maternal and paternal copies of the gene.
A possible mechanism of disomy is the elimination of an extra chromosome in a fetus with trisomy in the early stages of embryogenesis. The disease manifests itself if an extra chromosome originating from a normal gamete is eliminated.
Uniparental disomy has been described in cystic fibrosis when both mutant alleles are inherited from the same parent. In such cases, disomy mimics autosomal recessive inheritance.
In 20-30% of patients with Prader-Willi syndrome, who, according to cytogenetic studies, have a normal karyotype, disomy of the maternal chromosome 15 is detected using molecular biological methods. The paternal 15th chromosome is absent in such patients.
Uniparental disomy is thought to be the cause of intrauterine growth retardation, mental retardation, and microcephaly. These assumptions have not yet been confirmed by molecular biological studies.
Ticket number 29 SM. #2
Ticket number 30
Phenoty?p - (from the Greek word phainotip - I reveal, reveal) a set of characteristics inherent in an individual at a certain stage of development. The phenotype is formed on the basis of the genotype mediated by a number of environmental factors. In diploid organisms, dominant genes appear in the phenotype.
Phenotype - a set of external and internal signs of an organism acquired as a result of ontogenesis (individual development)
Despite a seemingly rigorous definition, the concept of phenotype has some uncertainties. First, most of the molecules and structures encoded by the genetic material are not visible in the appearance of the organism, although they are part of the phenotype. For example, this is the case with human blood types. Therefore, an extended definition of the phenotype should include characteristics that can be detected by technical, medical or diagnostic procedures. A further, more radical extension may include learned behavior or even the influence of an organism on environment and other organisms. For example, according to Richard Dawkins, the dam of beavers, as well as their incisors, can be considered a phenotype of beaver genes.
The phenotype can be defined as the "removal" of genetic information towards environmental factors. In the first approximation, we can talk about two characteristics of the phenotype: a) the number of outflow directions characterizes the number of environmental factors to which the phenotype is sensitive - the dimensionality of the phenotype; b) "range" of removal characterizes the degree of sensitivity of the phenotype to a given environmental factor. Together, these characteristics determine the richness and development of the phenotype. The more multidimensional the phenotype and the more sensitive it is, the further the phenotype is from the genotype, the richer it is. If we compare a virus, a bacterium, an ascaris, a frog and a person, then the richness of the phenotype in this series grows.
Genome - the whole set of hereditary material contained in the haploid set of chromosomes of cells of a given type of organism. It provides the formation of species characteristics of organisms in the course of their ontogenesis. Genotype - a set of genes formed during sexual reproduction in the process of fertilization when the genomes of two parent cells are combined, the genetic constitution of an organism, which is a set of all hereditary inclinations of its cells, enclosed in their chromosome set- karyotype. Phenotype - species and individual morphological, physiological and biochemical properties throughout individual development. The leading role in the formation of the phenotype is the hereditary information contained in the genotype. Along with this, the result of the hereditary program (in the genotype) depends on the conditions under which this process is carried out. In the case of heterozygosity, the development of this trait will depend on the interaction of allelic genes. Dominance is such an interaction of allelic genes, in which the manifestation of one of the alleles (A) does not depend on the presence of the other in the genotype (A '). This allele is dominant, the second is recessive (example: blood type). Incomplete dominance - the phenotype of heterozygotes BB' differs from the phenotype of homozygotes for both alleles (BB, B'B') by an intermediate manifestation of the trait. This happens because the allele capable of forming a normal trait is found in heterozygotes in a double dose of BB, and in homozygotes BB'. Genotypes differ in expressivity (degree of expression of the trait). Example: diseases in humans that manifest clinically in heterozygotes, and in homozygotes end in death. Codominance - each of the alleles manifests its effect, as a result - an intermediate version of the trait (Blood type, alleles that individually form 2 and 3 blood groups, together form 4). Allelic exclusion - a type of interaction of allelic genes in the genotype. For example, inactivation of one of the alleles in the composition of the X chromosome contributes to the fact that different cells of the body, mosaic on a functioning chromosome, phenotypically manifest different alleles.
Ticket number 31. Genetic homeostasis and mechanisms of its provision at different levels of life organization.
Genetic homeostasis - the ability of a population to maintain a dynamic balance of the genetic composition, which ensures its viability. Homeostatic systems have the following properties:
The instability of the system: tests how it is best to adapt. Striving for balance: all internal, structural and functional organization systems contributes to maintaining balance. Unpredictability: the resulting effect of a certain action can often differ from what was expected.
Mechanisms of homeostasis: feedback. When there is a change in variables, there are two main types of feedback, or feedback, to which the system reacts: Since the feedback serves to maintain the constancy of the system, it allows you to maintain homeostasis. For example, when the concentration carbon dioxide in the human body increases, the lungs receive a signal to increase their activity and exhale more carbon dioxide. Thermoregulation is another example of negative feedback. When body temperature rises (or falls), thermoreceptors in the skin and hypothalamus register the change, triggering a signal from the brain. This signal, in turn, causes a response - a decrease in temperature (or an increase). Positive feedback, which is expressed in an increase in the change in the variable. It has a destabilizing effect, so it does not lead to homeostasis. Positive feedback is less common in natural systems, but also has its uses. For example, in nerves the threshold electric potential causes the generation of a much larger action potential. Blood clotting and birth events are other examples of positive feedback. Robust systems need combinations of both types of feedback. While negative feedback allows you to return to a homeostatic state, positive feedback is used to move to a completely new (and quite possibly less desirable) state of homeostasis, a situation called "metastability". Such catastrophic changes can occur, for example, with an increase in nutrients in rivers with clear water, which leads to a homeostatic state of high eutrophication (algae overgrowth of the channel) and turbidity.
Ticket number 32 The sexual process and the evolution of its forms. Characteristics of gametes. Zygote drug. Problem for hemophilia
Ticket number 33 Transcription. Processing and splicing. Alternative splicing
Ticket number 34, 47. Biological rhythms and environmental factors. Chronobiology and chronomedicine, the concept of desynchronosis.
Chronobiology(from "Chrono", "Chronos" - "time") - a field of science that explores periodic (cyclic) phenomena that occur in living organisms in time, and their adaptation to solar and lunar rhythms. These cycles are referred to as biological rhythms (BR). Chronobiological research includes, but is not limited to, work in comparative anatomy, physiology, genetics, molecular biology, and behavioral biology. Other aspects include the study of development, reproduction, ecology and evolution of species.
Description. Synchronization of the level and duration of biological activity with external factors in living organisms occurs in many important biological processes. It happens
in animals (eating, sleeping, mating, wintering, migration, cellular regeneration, etc.),
in plants (leaf movements, photosynthesis, etc.).
The most important rhythm in chronobiology is the circadian rhythm, the roughly 24-hour cycle of physiological processes in plants and animals. (The word "circadian" comes from Latin, - "circadian" means "about", "about", and "dias" - "day", "day", that is, "circadian" or "circadian" is "around the clock") .
There are other important cycles:
· Infradian, longer term, such as the annual migration or reproduction cycles found in some animals, or the human menstrual cycle.
• ultradian rhythms, short cycles such as the 90-minute REM sleep cycle in humans, the 4-hour nasal cycle, or the 3-hour growth hormone production cycle.
Periodic rhythms commonly seen in marine animals often follow a (approximately) 12 hour transition from high tide to low tide and back again. Chronomedicine- This is a field of medicine that uses the concept of biological rhythms, which are studied within the framework of chronobiology. Biological rhythms are rhythmic manifestations of the temporal structure of the organism, therefore, chronomedicine is not limited to biological rhythms alone, but tries to consider the entire “temporal structure of the organism” as a whole. Chronomedicine (like chronobiology itself) is a young area of interdisciplinary research that is in the process of becoming . In chronomedicine, methods of mathematical processing of time series find their application, which are used to analyze the rhythmic manifestations of the physiological processes of the body. mathematical analysis rhythmic expressions). Causes of D.: mismatch of the functional rhythms of the body with the readings of external time sensors, for example, during transmeridional flights, flights over considerable distances in the latitudinal direction; stable mismatch in the phase of the rhythm sleep - wakefulness (work in the evening and night shifts); partial or complete absence of the usual time devices. Signs of D.: poor sleep, loss of appetite, irritability, decreased performance, apathy, lethargy. The duration of such disorders is from 1 to 14 days.
Ticket number 35. Prevention hereditary diseases and diseases with hereditary predisposition. Prenatal diagnosis, its methods and possibilities.
The limited treatment options for hereditary diseases and the predictable nature of the transmission of genes from generation to generation forced a focus on prevention as the most reliable and efficient way prevention of these diseases. Preventive methods include genetic testing, medical genetic counseling and prenatal diagnosis. The most effective measure for the prevention of hereditary diseases is the identification of heterozygous carriers of mutations, since in this case it is possible to prevent the birth of the first sick child in high-risk families. Relatives of the patient are likely to be heterozygous carriers of mutant alleles, therefore, in cases where possible, they are subject to examination in the first place. For diseases linked to sex, this applies to relatives in the female line - sisters, daughters and aunts of the proband. Their diagnosis is especially important, since the probability of having sick sons in the offspring of carriers of mutations is very high and does not depend on the spouse's genotype. In autosomal recessive diseases, half of the siblings of the parents and two-thirds of the healthy sibs of the patient will be heterozygous carriers of the mutation. Therefore, in those families where molecular identification of mutant alleles is fundamentally possible, it is necessary to examine the maximum number of relatives of a sick proband to identify heterozygous carriers. Sometimes in large families with branched pedigrees, it is possible to trace the inheritance of unidentifiable mutations using indirect methods of molecular diagnostics. For diseases that are common in certain populations or in certain ethnic groups and are caused by the presence of one or more predominant and easily identifiable mutant alleles, it is possible to conduct a total screening for heterozygous carriage of these mutations among certain population groups, for example, among pregnant women or among newborns. It is believed that such screening is economically justified if the procedure identifies alleles that make up at least 90-95% of all mutations of a given gene in the study population. Carriers of mutations identified during such examinations also constitute a risk group, and subsequently their spouses should be similarly tested. However, even if the mutation is found in only one of the parents, the probability of having a sick child is slightly higher than the population frequency, but, of course, much less than 25%. The specific value of this risk depends on the general frequency of mutations of the corresponding gene in the population. In such families (at the request of the parents), prenatal diagnosis can also be carried out and the inheritance of the mutant allele can be traced. In the absence of this mutation in the fetus, the prognosis is considered favorable, regardless of which alleles the child receives from the second spouse.
From a preventive point of view, it is advisable to divide all hereditary pathology into three categories:
1) newly emerging mutations (first of all, these are aneuploidies and severe forms of dominant mutations);
2) inherited from previous generations (both genetic and chromosomal);
3) diseases with hereditary predisposition.
There are primary prevention of hereditary pathology and secondary prevention of hereditary pathology.
Under primary prevention understand such measures that should prevent the conception or birth of a sick child.
Prevention of newly emerging mutations should be reduced to a decrease in the rate of the mutation process. The latter is intense.
The modern basis for the prevention of hereditary pathology is theoretical developments in the field of human genetics and medicine, which made it possible to understand:
1) the molecular nature of hereditary diseases, the mechanisms and processes of their development in the pre and postnatal period;
2) patterns of conservation of mutations (and sometimes distribution) in families and populations;
3) the processes of occurrence and formation of mutations in germline and somatic cells.
Prenatal diagnosis- prenatal diagnostics, in order to detect pathology at the stage of intrauterine development. Allows you to detect more than 90% of fetuses with Down syndrome (trisomy 21); trisomy 18 (known as Edwards syndrome) about 97%, more than 40% of cardiac developmental disorders, etc. If the fetus has a disease, parents, with the help of a consultant doctor, carefully weigh the possibilities of modern medicine and their own in terms of the rehabilitation of the child. As a result family decides on the fate of this child and decides whether to continue bearing or terminate the pregnancy. Prenatal diagnosis also includes determining paternity in early pregnancy, as well as determining the sex of the child.
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.
During the post stage, the body 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.
Definition 3
Embryoization - this is a phenomenon when the embryonic period is extended due to the nutrition of the embryo with the resources of the mother's body or reserve nutrients of the egg.
Embryoization is inherent in reptiles, fish, birds and mammals. biological significance This phenomenon consists 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 characteristics structures 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 changes take place. internal organs larvae and the formation of tissues and organs of an adult insect.
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 characteristic of most higher plants, multicellular algae, tapeworms and annelids, mollusks, fish, and 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 propagation. 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.
In postembryonic ontogeny, the juvenile and puberty periods, as well as the period of old age, ending in death, are distinguished.
juvenile period. This period (from lat. juvenilis- young) is determined by the time from the birth of the organism to puberty. It proceeds in different ways and depends on the type of ontogenesis of organisms. This period is characterized by either direct or indirect development.
In the case of organisms that are characterized by direct development (many invertebrates, fish, reptiles, birds, mammals, humans), hatched from egg shells or newborns are similar to adult forms, differing from the latter only in smaller sizes, as well as underdevelopment of individual organs and imperfect proportions of the body (Fig. 30).
A characteristic feature of the growth in the juvenile period of organisms subject to direct development is that there is an increase in the number and size of cells, and body proportions change. The growth of a person in different periods of his ontogenesis is shown in Fig. 31. The growth of different human organs is uneven. For example, the growth of the head ends in childhood, the legs reach a proportional size by about 10 years. The external genitalia grow very quickly at the age of 12-14 years. Distinguish between definite and indefinite growth. A certain growth is characteristic of organisms that stop growing by a certain age,
e.g. insects, mammals, humans. Indefinite growth is characteristic of organisms that grow throughout their lives, such as molluscs, fish, amphibians, reptiles, and many plant species.
Rice. thirty. Direct and indirect development of organisms of different species
In the case of indirect development, organisms undergo transformations called metamorphoses (from lat. metamorphosis- transformation).
Rice. 31. Growth and development in different periods of human ontogenesis
They represent modifications of organisms in the process of development. Metamorphoses are widely found in coelenterates (hydras, jellyfish, coral polyps), flatworms (fasciolae), roundworms (roundworms), molluscs (oysters, mussels, octopuses), arthropods (crayfish, river crabs, lobsters, shrimps, scorpions, spiders, ticks, insects) and even in some chordates (tunicates and amphibians). At the same time, complete and incomplete metamorphoses are distinguished. The most expressive forms of metamorphoses are observed in insects that undergo both incomplete and complete metamorphoses.
An incomplete transformation is such a development in which an organism comes out of the egg membranes, the structure of which is similar to the structure of an adult organism, but the dimensions are much smaller. Such an organism is called a larva. In the process of growth and development, the size of the larvae increases, but the existing chitinous cover prevents a further increase in body size, which leads to molting, i.e., shedding of the chitinized cover, under which there is a soft cuticle. The latter straightens out, and this is accompanied by an increase in the size of the animal. After several molts, the animal reaches maturity. Incomplete transformation is typical, for example, in the case of the development of bedbugs.
Complete transformation is such a development in which a larva is released from the egg membranes, which is significantly different
in structure from adults. For example, in butterflies and many insects, caterpillars are larvae. Caterpillars are subject to molting, and they can molt several times, then turning into pupae. From the latter, adult forms (imago) develop, which do not differ from the original ones.
In vertebrates, metamorphoses are found among amphibians and bony fishes. The larval stage is characterized by the presence of provisional organs, which either repeat the traits of their ancestors or have a clearly adaptive value. For example, a tadpole, which is the larval form of a frog and repeats the features of the original form, is characterized by a fish-like shape, the presence of gill breathing and one circle of blood circulation. The adaptive features of tadpoles are their suckers and long intestines. The larval forms are also characterized by the fact that, in comparison with adult forms, they turn out to be adapted to life in completely different conditions, occupying a different ecological niche and a different place in the food chain. For example, frog larvae have gill breathing, while adult forms are pulmonary. Unlike adult forms, which are carnivorous creatures, frog larvae feed on plant foods.
The sequence of events in the development of organisms is often referred to as life cycles, which can be simple or complex. The simplest cycles of development are typical, for example, for mammals, when an organism develops from a fertilized egg, which again produces eggs, etc. Complex biological cycles are cycles in animals, which are characterized by development with metamorphoses. Knowledge of biological cycles practical value, especially in cases where the organisms are causative agents or vectors of pathogens in animals and plants.
Development and differentiation associated with metamorphosis are the result of natural selection, due to which many larval forms, such as insect caterpillars and frog tadpoles, are better adapted to the environment than adult sexually mature forms.
puberty. This period is also called mature, and it is associated with the sexual maturity of organisms. The development of organisms during this period reaches a maximum.
On growth and development in the postembryonic period big influence provided by environmental factors. For plants, the decisive factors are light, humidity, temperature, and the quantity and quality of nutrients in the soil. For animals, complete feeding is of paramount importance (the presence of proteins, carbohydrates, lipids, mineral salts, vitamins, microelements in the feed). Oxygen, temperature, light (vitamin D synthesis) are also important.
The growth and individual development of animal organisms are subject to neurohumoral regulation by humoral and nervous mechanisms of regulation. Hormone-like active substances, called phytohormones, have been found in plants. The latter affect the vital functions of plant organisms.
In the cells of animals in the process of vital activity, chemically active substances are synthesized that affect the processes of vital activity. Nerve cells of invertebrates and vertebrates produce substances called neurosecrets. The glands of endocrine, or internal, secretion also secrete substances that are called hormones. The endocrine glands, in particular those related to growth and development, are regulated by neurosecretions. In arthropods, the regulation of growth and development is very well illustrated by the effect of hormones on molting. The synthesis of larval secretion by cells is regulated by hormones that accumulate in the brain. In a special gland in crustaceans, a hormone is produced that inhibits molting. The levels of these hormones determine the frequency of shedding. In insects, hormonal regulation of egg maturation and ongoing diapauses have been established.
In vertebrates, the endocrine glands are the pituitary, pineal, thyroid, parathyroid, pancreas, adrenals, and gonads, which are closely related to each other. The pituitary gland in vertebrates produces a gonadotropic hormone that stimulates the activity of the gonads. In humans, the pituitary hormone affects growth. With a deficiency, dwarfism develops, with an excess - gigantism. The pineal gland produces a hormone that affects the seasonal fluctuations in the sexual activity of animals. Thyroid hormone affects the metamorphosis of insects and amphibians. In mammals, underdevelopment of the thyroid gland leads to growth retardation, underdevelopment of the genital organs. In humans, due to a defect in the thyroid gland, ossification, growth
(dwarfism), does not occur puberty, stops mental development(cretinism). The adrenal glands produce hormones that affect the metabolism, growth and differentiation of cells. The gonads produce sex hormones that determine secondary sexual characteristics. Removal of the gonads leads to irreversible changes in a number of signs. For example, in castrated roosters, the growth of the comb stops, the sexual instinct is lost. A castrated man acquires an outward resemblance to a woman (a beard and hair do not grow on the skin, fat is deposited on the chest and in the pelvic area, the timbre of the voice is preserved, etc.).
Plant phytohormones are auxins, cytokinins and gibberellins. They regulate the growth and division of cells, the formation of new roots, the development of flowers and other properties of plants.
At all periods of ontogenesis, organisms are capable of restoring lost or damaged parts of the body. This property of organisms is called regeneration, which is physiological and reparative.
Physiological regeneration - it is the replacement of lost parts of the body in the process of life of the organism. Regenerations of this type are very common in the animal kingdom. For example, in arthropods, it is represented by molting, which is associated with growth. In reptiles, regeneration is expressed in the replacement of the tail and scales, in birds - feathers, claws and spurs. In mammals, an example of physiological regeneration is the annual shedding of deer antlers.
Reparative regeneration - it is the restoration of a body part of an organism that has been torn away by force. Regeneration of this type is possible in many animals, but its manifestations are different. For example, it is frequent in hydras and is associated with the reproduction of the latter, since the whole organism regenerates from a part. In other organisms, regeneration manifests itself in the form of the ability of individual organs to restore after the loss of some part. In humans, epithelial, connective, muscle and bone tissues have a sufficiently high regenerative capacity.
Plants of many species are also capable of regeneration.
Regeneration data have great importance not only in biology. They are widely used in agriculture in medicine, in particular in surgery.
Old age as a stage of ontogenesis. Old age is the penultimate stage of animal ontogenesis, and its duration is determined by
the total life expectancy, which serves as a species trait and is not the same for different animals. Old age has been most accurately studied in humans.
There are various definitions of human old age. In particular, one of the most popular definitions is that old age is the accumulation of successive changes that accompany an increase in the age of an organism and increase the likelihood of its illness or death. The science of human old age is called gerontology (from the Greek. geron- old man, old man logos- the science). Its task is to study the patterns of age transition between maturity and death.
Scientific research in gerontology extends to different areas, from studies of changes in the activity of cellular enzymes to elucidation of the influence of psychological and sociological mitigation of environmental stresses on the behavior of old people.
In the case of man, physiological old age is distinguished; old age associated with calendar age; and premature aging due to social factors and disease. In accordance with WHO recommendations, the age of about 60-75 years should be considered an old age of a person, and the age of 75 years or more should be considered old.
A person's old age is characterized by a number of external and internal signs.
Among the external signs of old age, the most noticeable are a decrease in the smoothness of movements, a change in posture, a decrease in skin elasticity, body weight, muscle firmness and elasticity, the appearance of wrinkles on the face and other parts of the body, and tooth loss. So, for example, according to generalized data, a person at the age of 30 loses 2 teeth (as a result of loss), at 40 years old - 4 teeth, at 50 years old - 8 teeth, and at 60 years old - already 11 teeth. The first signal system undergoes noticeable changes (the sharpness of the sense organs is dulled). For example, the maximum distance at which healthy people distinguish these or those identical sounds, at 20-30 years old it is 12 m, at 50 years old - 10 m, at 60 years old - 7 m, and at 70 years old - only 4 m. The second signal system also changes noticeably (speech intonation changes, voice becomes muffled).
Among the internal signs, first of all, one should name such signs as the reverse development (involution) of organs. There is a decrease in the size of the liver and kidneys, as well as the amount
The presence of nephrons in the kidneys (almost by half by the age of 80), which reduces the functionality of the kidneys and affects the water and electrolyte metabolism. Reduced elasticity blood vessels, blood perfusion of tissues and organs decreases, peripheral vascular resistance increases. Inorganic salts accumulate in the bones, cartilage changes (calcified), and the ability of organs to regenerate decreases. Significant changes occur in cells, division and restoration of their functional tone slow down, water content decreases, activity of cellular enzymes decreases, coordination between assimilation and dissimilation is disrupted. In the brain, protein synthesis is disrupted, resulting in the formation of abnormal proteins. Viscosity rises cell membranes, the synthesis and utilization of sex hormones are disrupted, changes occur in the structure of neurons. Structural changes in the proteins of the connective tissue and the elasticity of this tissue occur. Immunological reactions are weakened, the possibility of autoimmune reactions increases. The functions of the endocrine systems, in particular the sex glands, are reduced. The behavior of other traits in old age is shown in Fig. 32.
Rice. 32. Changes in some signs of a person with age: 1 - the speed of nerve impulses; 2 - level of basic metabolism; 3 - cardiac index; 4 - the level of renal filtration by insulin; 5 - respiratory volumes of the lungs; 6 - the level of plasma flow in the kidneys
Aspirations to understand the nature of body aging arose long ago. In ancient Greece, Hippocrates believed that aging is associated with excesses in food, insufficient exposure to fresh air. According to Aristotle, aging is due to the consumption of thermal energy by the body. The importance of food as a factor in aging was also noted by Galen. But long time there was not enough scientific data for an objective understanding of this problem. Only in the 19th century Some progress has been made in the study of aging, and theories of aging have begun to emerge.
One of the first most famous theories of aging of the human body is the theory of the German doctor X. Hufeland (1762-1836), who attached importance to longevity of labor activity. We have heard his statement that not a single lazy person lived to an advanced age. Even more famous endocrine theory of aging, which originates from experiments carried out even in the middle of the century before last by Berthold (1849), who showed that the transplantation of testes from one animal to another is accompanied by the development of secondary sexual characteristics. Later, the French physiologist C. Brown-Séquard (1818-1894), based on the results of injecting himself with extracts from the testicles, argued that these injections produce a beneficial and rejuvenating effect. At the beginning of the XX century. there has already been a belief that the onset of old age is associated with the extinction of the activity of the endocrine glands, in particular the gonads. In the 20-30s. 20th century on the basis of this belief, many operations have been done in different countries to rejuvenate the elderly or old people. For example, G. Steinakh in Austria bandaged the spermatic cords of men, which led to the cessation of the external secretion of the gonads and allegedly to some rejuvenation. S.A. Voronov in France transplanted testicles from young animals to old ones and from monkeys to men, and Tushnov in the USSR rejuvenated roosters by injecting them with gonadal histolysates. All these operations led to some effects, but only temporary. After these impacts, the aging processes continued, and even more intensively.
At the beginning of the XX century. arose microbiological theory of aging, whose creator was I.I. Mechnikov, who distinguished between physiological and pathological old age. He believed that human old age is pathological, i.e. premature. The basis of the ideas of I.I. Mechnikov was the doctrine of orthobiosis (orthos-
right, bios- life), according to which the main cause of aging is damage to nerve cells by intoxication products resulting from putrefaction in the large intestine. Developing the doctrine of a normal lifestyle (observance of hygiene rules, regular work, abstinence from bad habits), I.I. Mechnikov also proposed a method for suppressing putrefactive intestinal bacteria by consuming fermented milk products.
In the 30s. 20th century received widespread theory about the role of the central nervous system(CNS) in aging. The creator of this theory is I.P. Pavlov, who established the integrating role of the CNS in the normal functioning of organisms. Followers of I.P. Pavlova in animal experiments showed that premature aging is caused by nervous shocks and prolonged nervous strain.
Worth a mention theory of age-related changes in connective tissue, formulated in the 30s. 20th century A.A. Bogomolets (1881-1946). He believed that connective tissue (bone tissue, cartilage, tendons, ligaments, and fibrous connective tissue) provides the physiological activity of the body, and that changes in the colloidal state of cells, loss of their turgor, etc., determine age-related changes in organisms. Current evidence points to the importance of calcium accumulation in connective tissues, as it contributes to the loss of its elasticity, as well as the sealing of blood vessels.
Modern approaches to understanding the essence and mechanisms of aging are characterized by the widespread use of data from physical and chemical biology, and in particular the achievements of molecular genetics. The most common modern ideas about the mechanism of aging come down to the fact that in the course of life somatic mutations accumulate in the cells of the body, resulting in the synthesis of defective proteins or unrepaired DNA-to-protein cross-links. Since defective proteins play a dose-integrating role in cellular metabolism, this leads to aging. In the case of cultured fibroblasts, proteins and mRNA associated with old cells have been shown to inhibit DNA synthesis in young fibroblasts.
There is also a well-known hypothesis, according to which aging is considered the result of changes in mitochondrial metabolites with subsequent impairment of enzyme functions.
In humans, the existence of genes that determine the timing of the development of hereditary degenerative processes associated with aging has been shown. A number of researchers believe that the cause of aging is changes in the body's immune defense system, in particular, autoimmune reactions to body structures that are of vital importance. Finally, in explaining the mechanisms of aging, experts pay great attention to protein damage associated with the formation of free radicals. Finally, sometimes they attach importance to hydrolases released after the breakdown of lysosomes, which destroy cells.
However, an exhaustive theory of aging still has not been created, since it is clear that none of these theories can independently explain the mechanisms of aging.
Death. Death is the final stage of ontogeny. The question of death in biology occupies a special place, because the feeling of death "... is completely instinctively inherent in human nature and has always been one of the greatest concerns of man" (I.I. Mechnikov, 1913). Moreover, the question of death has been and is at the center of attention of all philosophical and religious teachings, although the philosophy of death in different historical times was presented differently. In the ancient world, Socrates and Plato proved the immortality of the soul, while Aristotle denied the Platonic idea of the immortality of the soul and believed in the immortality of the human spirit, which continues to live after the death of a person. Cicero and Seneca also recognized a future life, but Marcus Aurelius considered death a natural phenomenon that should be accepted resignedly. In the XVIII century. I. Kant and I. Fichte (1762-1814) also believed in a future life, and G. Hegel adhered to the belief that the soul is absorbed by the “absolute being”, although the nature of this “being” was not disclosed.
In accordance with all known religious teachings earthly life of a person continues after his death, and a person must tirelessly prepare for this future death. However, naturalists and philosophers who do not recognize immortality believed and still believe that death is, as I.I. Mechnikov, the natural outcome of the life of the organism. A more figurative definition of death is that it "... is a clear victory of meaninglessness over meaning, chaos over the cosmos" (V. Solovyov, 1894).
Scientific evidence suggests that in unicellular organisms (plants and animals), death should be distinguished from termination.
of their existence. Death is their destruction, while the cessation of existence is associated with their division. Consequently, the fragility of unicellular organisms is compensated by their reproduction. In multicellular plants and animals, death is in the full sense of the word the end of the life of the organism.
In humans, the likelihood of death increases during puberty. In developed countries, in particular, the likelihood of death increases almost exponentially after age 28.
Distinguish between clinical and biological death of a person. Clinical death is expressed in loss of consciousness, cessation of heartbeat and breathing, but most cells and organs still remain alive. Self-renewal of cells occurs, intestinal peristalsis continues. Clinical death does not "reach" biological death, because it is reversible, since it is able to clinical death can be brought back to life. For example, dogs are "returned" to life after 5-6 minutes, a person - after 6-7 minutes from the onset of clinical death. Biological death is characterized by the fact that it is irreversible. Stopping the heartbeat and breathing is accompanied by the cessation of self-renewal processes, cell death and decomposition. However, cell death does not begin in all organs at the same time. First, the cerebral cortex dies, then the epithelial cells of the intestine, lungs, liver, muscle cells, and heart die.
Measures for resuscitation (revival) of organisms are based on the concept of clinical death, which is of exceptional importance in modern medicine.
Postembryonic development
May be direct or indirect(accompanied by metamorphosis (transformation)).
With direct development the newly appeared organism is similar in structure to the parent and differs from it only in size and incomplete development organs.
Direct postembryonic development:
Direct development is characteristic of humans and other mammals, birds, reptiles, and some insects.
In human development, the following periods are distinguished: childhood, adolescence, youth, youth, maturity, old age. Each period is characterized by a number of changes in the body.
Aging and death are the last stages of individual development. Aging is characterized by many morphological and physiological properties, leading to a general decrease in vital processes and the body's resistance. The causes and mechanisms of aging are not fully understood.
Death ends individual existence. It can be physiological if it occurs as a result of aging, and pathological if it is caused prematurely by some external factor (injury, illness).
Indirect postembryonic development:
Metamorphosis represents a profound transformation in the structure of the body, as a result of which the larva turns into an adult insect. Depending on the nature of postembryonic development in insects, two types of metamorphosis are distinguished:
incomplete(hemimetaboly), when the development of an insect is characterized by the passage of only three stages - eggs, larvae and the adult phase (adult);
full(holometaboly), when the transition of the larva to the adult form is carried out at an intermediate stage - the pupal stage.
A chick hatched from an egg or a kitten born is similar to adult animals of the corresponding species. However, in other animals (for example, amphibians, most insects), development proceeds with sharp physiological changes and is accompanied by the formation of larval stages. In this case, all parts of the body of the larva undergo significant changes. The physiology and behavior of animals are also changing. The biological significance of metamorphosis is that at the stage of the larva the organism grows and develops not at the expense of the reserve nutrients of the egg, but it can feed on its own.
A larva emerges from the egg, usually simpler 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. With incomplete metamorphosis, the replacement of larval organs occurs gradually, without cessation of active nutrition and movement of the organism. Complete metamorphosis includes the pupal stage, in which the larva transforms into an adult animal.
In ascidians (type chordates, subtype larval-chordates), a larva is formed that has all the main features of chordates: chord, neural tube, gill slits in the pharynx. The larva swims freely, then attaches itself to some solid surface on the bottom of the sea and undergoes metamorphosis: the tail disappears, the notochord, muscles, neural tube break up into separate cells, most of which are phagocytosed. Only a group of cells remains from the nervous system of the larva, giving rise to the nerve ganglion. The structure of an adult ascidian, leading an attached lifestyle, does not at all resemble the usual features of the organization of chordates. Only knowledge of the features of ontogeny makes it possible to determine the systematic position of ascidians. The structure of the larva indicates their origin from chordates that led a free lifestyle. In the process of metamorphosis, ascidians switch to a sedentary lifestyle, and therefore their organization is simplified.
Indirect development is characteristic of amphibians
The frog larva - the tadpole - resembles a fish. He swims near the bottom, pushing himself forward with a tail framed by a fin and breathes first with external gills protruding in tufts on the sides of the head, and later with internal gills. He has one circle of blood circulation, a two-chambered heart, there is a lateral line. All these are structural features of fish.
1 week, body length 7 mm - Hatches from the mucous capsule. There are external gills, a tail, a mouth with horny jaws; under mouth opening mucous glands.
2 weeks, body length 9 mm - External gills begin to atrophy, a gill cover forms over the internal gills. The eyes are well developed.
4 weeks, body length 12 mm - Loss of external gills and mucous glands. Splash develops. The tail expands and helps to swim.
7 weeks, body length 28 mm - The kidneys of the hind limbs appear.
9 weeks, body length 35 mm - Hind limbs are fully formed, but not used for swimming. The head begins to expand.
11-12 weeks, body length 35 mm - The left forelimb comes out through the spiracle, and the right one is covered by the gill cover. The hind limbs are used for swimming.
13 weeks, body length 25 mm - Eyes enlarge, mouth expands.
14 weeks, body length 20 mm - The tail begins to dissolve.
16 weeks, body length 15mm - All external larval signs disappeared. The frog comes out on land.
Amphibians grow all their lives, but the older, the slower.
In a fish, a fry appears from an egg, which grows and turns into an adult.
The rate of metamorphosis depends on the amount of food, temperature and internal factors. For example, a frog larva - a tadpole - feeds on plants, and an adult frog feeds on insects. The tadpole and caterpillar differ from adult forms in structure, appearance, lifestyle, nutrition.
Butterfly larvae, called caterpillars, have an elongated, notched body, resembling worms with chopped ends of the body. The mouth apparatus of caterpillars, unlike such adult insects, is gnawing. Spinning glands open on the lower lip, secreting a secret that solidifies in air into silk threads. On the chest, the larvae, like adults, have three pairs of segmented legs, but they use them only to capture food and for support. To move the caterpillar, non-segmented fleshy abdominal pseudopods are used, on the soles of which
there are small hooks. The vast majority of caterpillars feed on plant foods. Their way of life is very diverse. Development with complete transformation.