Subkingdom Multicellular - definition, signs and characteristics. General characteristics of multicellular animals Characteristics of unicellular and multicellular organisms

home » Biology Subkingdom Multicellular - definition, signs and characteristics. General characteristics of multicellular animals Characteristics of unicellular and multicellular organisms

Multicellular organisms (Metazoa) - these are organisms consisting of a set of cells, groups of which specialize in performing certain functions, creating qualitatively new structures: tissues, organs, organ systems. In most cases, due to this specialization, individual cells cannot exist outside the body. The subkingdom Multicellular has about 30 types. The organization of the structure and life of multicellular animals differs in many ways from the organization of unicellular ones.

■ In connection with the appearance of organs, formed body cavity- the space between the organs, which ensures their relationship. The cavity can be primary secondary and mixed.

■ Due to the complication of lifestyle, radial (radial) or bilateral (bilateral) symmetry, which gives grounds to separate multicellular animals as radially symmetric and binary symmetric.

■ As food needs grow, efficient means of transportation emerge that allow active foraging, resulting in musculoskeletal system.

■ multicellular animals require much more food than unicellular animals, and therefore most animals switch to eating solid organic food, which leads to digestive system.

■ In most organisms, the outer covers are impermeable, so the exchange of substances between the organism and the environment occurs through limited areas of its surface, which leads to the appearance respiratory system.

■ As the size increases, circulatory system, which carries blood due to the work of the heart or pulsating vessels.

■ Formed excretory systems for the withdrawal of exchange products

■ Regulatory systems emerge - nervous And endocrine, which coordinate the work of the whole organism.

■ Due to the appearance nervous system new forms of irritability appear - reflexes.

■ The development of multicellular organisms from a single cell is a long and complex process, and therefore life cycles become more complicated, which will certainly include a number of stages: zygote - embryo - larva (baby) - young animal - adult animal - sexually mature animal - an aging animal - an animal has died.

General signs of the structure and life of representatives of the Sponge type

Sponges - multicellular bilayered radially or asymmetric animals, the body of which is riddled with pores. About 5000 species of freshwater and sea sponges belong to the type. The vast majority of these species inhabit tropical and subtropical seas, where they are found at depths up to 500 m. However, among the sponges, there are also deep-sea forms that were found at a depth of 10,000 - 11,000 m (for example, sea brushes). There are 29 species in the Black Sea, 10 species in fresh waters of Ukraine. Sponges belong to the most primitive multicellular organisms, since tissues and organs are not clearly expressed in them, although cells perform various functions. The main reason preventing the mass distribution of sponges is the lack of an appropriate substrate. Most sponges cannot live on muddy bottoms because the mud particles clog their pores, leading to the death of the animal. Salinity and mobility of water, temperature have a great influence on distribution. The most common features of sponges are: 1 ) the presence of pores in the walls of the body 2) absence of tissues and organs; 3) the presence of a skeleton in the form of needles or fibers; 4) well developed regeneration and etc.

Widespread from freshwater forms body sponge(Spongilla lacustris), which lives on the stony soils of water bodies. The green color is due to the presence of algae cells in their protoplasm.

structural features

Body multicellular, stalked, bushy, cylindrical, funnel-shaped, but most often in the form of a bag or glass. Sponges lead an attached lifestyle, so in their body there is the foundation for attaching to the substrate, and on top - a hole ( mouth), which leads to a Triolny (paragastric) cavities. The walls of the body are permeated with many pores through which water enters this body cavity. The walls of the body are formed from two layers of cells: the outer - pinacoderm and internal - choanoderma. Between these layers there is a structureless gelatinous substance - mesoglea that contains cells. Sponge body sizes - from a few millimeters to 1.5 m (sponge cup of neptune).

Sponge structure: 1 - mouth; 2 - pinacoderma; 3 - choanoderma; 4 - time; 5 - mesoglea; 6 - archeocyte; 7 - base; 8 - triaxial branch; 9 - atrial cavity; 10 - spicules; 11 - amebocytes; 12 - colencite; 13 - porocyte; fourteen - pinacocyte

Diversity of sponge cells and their functions

cells	Location	functions
Pinacocytes	Pinacoderma	squamous cells that form the surface epithelium
Porocytes	Pinacoderma	Cells with an intracellular time-channel capable of contracting and opening or closing it
choanocytes	Choanoderma	Cylindrical cells with a long flagellum that create a flow of water and are able to absorb nutrient particles and transfer them to the mesoglea
Colencites	mesoglea	Fixed stellate cells, which are connective tissue supporting elements
Sclerocytes	mesoglea	Cells from which the skeletal formations of sponges develop - spicules
	mesoglea	Cells that are interconnected with the help of processes and provide some reduction in the body of sponges
amebocytes	mesoglea	Mobile cells that carry out the digestion of food and the spread of nutrients throughout the body of the sponge
archeocytes	mesoglea	Reserve cells that are able to transform into all other cells and give rise to germ cells

Features of the organization of sponges are reduced to three main types:

ASCON - body with a paragastric cavity lined with choanocytes (in limestone sponges)

Seacon- a body with thickened walls, into which sections of the paragastric cavity protrude, forming flagellar pockets (in glass sponges)

leukone- a body with thick walls, in which small flagellar chambers are distinguished (in ordinary sponges).

Covers. The body is covered with a squamous epithelium formed by pinacocytes.

Cavity body is called paragastric and is lined with choanocytes.

Features of life processes

Support provided by the skeleton, it can be limestone (spicule with CaCO3), silicon (spicule with SiO2) or horny (from collagen fibers and spongin substance, which contains a significant amount of iodine).

Motion. Adult sponges are not capable of active movement and lead an attached lifestyle. Some minor contractions of the body are carried out thanks to myocytes, which can thus respond to irritation. Amebocytes are capable of moving inside the body due to pseudopodia. Sponge larvae, unlike adults, are able to move vigorously in water due to the coordinated work of flagella, which in most cases almost completely cover the surface of the body.

Nutrition in sponges is passive and is carried out by a continuous flow of water through the body. Due to the rhythmic work of the flagella hoonocyte water enters the pores, enters the paragastric cavity and is brought out through the mouths. Dead remains of animals and plants suspended in water, as well as microorganisms, are carried away by choanocytes, transferred to amoebocytes, where they are digested and carried by them throughout the body.

Digestion in sponges, it is intracellular. Amebocytes' interest in nutrient particles occurs by phagocytosis. Undigested residues are thrown into the body cavity and excreted.

Transportation of substances inside the body is carried out by amoebocytes.

Breath occurs throughout the body. For respiration, oxygen dissolved in water is used, which is absorbed by all cells. Carbon dioxide is also removed in a dissolved state.

Selection undigested residues and metabolic products occurs along with water through the mouth.

Process regulation is carried out with the participation of cells that are able to contract or make movements - porocyte, myocytes, choanocytes. The integration of processes at the level of the organism is almost not developed.

Irritability. Sponges react very weakly even to the strongest irritations, and their transmission from one area to another is almost imperceptible. This indicates the absence of a nervous system in sponges.

reproduction asexual and sexual. Asexual reproduction is carried out by external and internal budding, fragmentation, longitudinal division, etc. In the case of external budding, the daughter individual is formed on the mother and, as a rule, contains all types of cells. In rare forms, the kidney separates (for example, in sea orange), and in the colonial - retains a connection with the mother's organism. IN body sponges and in other freshwater sponges, in addition to external, internal budding is also observed. In the second half of summer, when the water temperature drops from archaeocytes, internal buds are formed - gemmules. For the winter, the bodyagi's body dies off, and the gemmules sink to the bottom and, protected by a shell, hibernate. In the spring, a new sponge develops from it. As a result of fragmentation, the body of the sponge breaks up into parts, each of which, under favorable conditions, gives rise to a new organism. Sexual reproduction occurs with the participation of gametes, which are formed from archaeocytes in mesoglea. Most sponges are hermaphrodites (sometimes dioecious). In the case of sexual reproduction, the mature spermatozoon of one sponge leaves the mesoglea through the mouth and enters the cavity of the other with the flow of water, where it is delivered to the mature egg cell with the help of amoebocytes.

Development indirect(with transformation). Cleavage of the zygote and the formation of the larva occurs mainly inside the maternal organism. The larva, which has flagella, exits through the mouth into the environment, attaches to the substrate and turns into an adult sponge.

Regeneration well developed. Sponges have a very high level of regeneration, which ensures the reproduction of a whole independent organism, even from the very piece of the sponge's body. For sponges inherent and somatic embryogenesis - formation, development of a new individual from cells of the body that are not adapted for reproduction. If you pass the sponge through a sieve, you can get a filtrate containing living individual cells. These cells remain viable for several days and, with the help of pseudopodia, actively move and gather in groups. These groups turn into small sponges after 6-7 days.

Multicellular animals form the largest group of living organisms on the planet, numbering more than 1.5 million species. Leading their origin from the simplest, they have undergone significant transformations in the process of evolution associated with the complication of organization.

Coelenterates: There are more than 9 thousand species of coelenterates. These are lower, predominantly marine, multicellular animals attached to the substrate or floating in the water column. The body is saccular, formed by two layers of cells: the outer - ectoderm, and the inner - endoderm, between which there is a structureless substance - mesoglea.

Reproduction occurs both asexually and sexually. Incomplete to the end asexual reproduction - budding - leads in a number of species to the formation of colonies.

Sponges are multicellular animals:

Sponges are characterized by a modular structure, often associated with the formation of colonies, as well as the absence of true tissues and germ layers. Unlike true multicellular animals, sponges lack the muscular, nervous, and digestive systems. The body is composed of an integumentary layer of cells, subdivided into pinacoderm and choanoderm, and a jelly-like mesochyl permeated by the channels of the aquifer system and containing skeletal structures and cellular elements. The skeleton in different groups of sponges is represented by various protein and mineral (calcareous or silicic) structures. Reproduction is carried out both sexually and asexually.

Multicellular:

One of the most important features of the organization of multicellular organisms is the morphological and functional difference between the cells of their body. Over the course of evolution, similar cells in the body of multicellular animals specialized in performing certain functions, which led to the formation of tissues.

Different tissues united into organs, and organs - and organ systems. To implement the relationship between them and coordinate their work, regulatory systems were formed - nervous and endocrine. Thanks to the nervous and humoral regulation of the activity of all systems, a multicellular organism functions as an integral biological system.

The prosperity of a group of multicellular animals is associated with the complication of the anatomical structure and physiological functions. Thus, an increase in body size led to the development of the alimentary canal, which allowed them to eat large food material, which supplies a large amount of energy for the implementation of all life processes. The developed muscular and skeletal systems ensured the movement of organisms, the maintenance of a certain body shape, protection and support for organs. The ability to actively move allowed animals to search for food, find shelter and settle.

With an increase in the size of the body of animals, the need arose for the appearance of intratransport circulatory systems that deliver life support means - nutrients, oxygen, and also remove end products of metabolism to tissues remote from the surface of the body and organs.

Liquid tissue - blood - became such a circulatory transport system.

The intensification of respiratory activity went in parallel with the progressive development of the nervous system and sensory organs. The central sections of the nervous system moved to the anterior end of the animal's body, as a result of which the head section became isolated. This structure of the anterior part of the animal's body allowed him to receive information about changes in environment and respond appropriately to them.

According to the presence or absence of an internal skeleton, animals are divided into two groups - invertebrates (all types except Chordates) and vertebrates (Chordates).

Depending on the origin of the mouth opening in an adult organism, two groups of animals are distinguished: primary and secondary-stomes. Protostomes unite animals in which the primary mouth of the embryo at the gastrula stage - the blastopore - remains the mouth of an adult organism. These include animals of all types except echinoderms and chordates. In the latter, the primary mouth of the embryo turns into an anus, and the true mouth is formed a second time in the form of an ectodermal pocket. For this reason, they are called deuterostomes.

According to the type of body symmetry, a group of radiant, or radially symmetrical, animals (types of Sponge, Coelenterates and Echinoderms) and a group of bilaterally symmetrical (all other types of animals) are distinguished. Radiation symmetry is formed under the influence of the sedentary lifestyle of animals, in which the entire organism is placed in relation to environmental factors in exactly the same conditions. These conditions form the arrangement of identical organs around the main axis passing through the mouth to the attached pole opposite to it.

Bilaterally symmetrical animals are mobile, have one plane of symmetry, on both sides of which there are various paired organs. They distinguish between left and right, dorsal and ventral sides, anterior and posterior ends of the body.

Multicellular animals are extremely diverse in structure, life characteristics, different in size, body weight, etc. Based on the most significant common structural features, they are divided into 14 types, some of which are discussed in this manual.

In multicellular organisms, ontogenesis usually begins with the formation of a zygote and ends with death. At the same time, the organism not only grows, increasing in size, but also goes through a number of different life phases, each of which has a special structure, functions differently, and in some cases radically different way of life. The process of embryonic development of multicellular animals includes three main stages: cleavage, gastrulation, and primary organogenesis. Embryogenesis begins with the formation of a zygote.

Consider the stages of embryonic development of a multicellular animal using the example of a lake frog. Within a few hours (in other species of vertebrates, even after a few minutes) after the introduction of the sperm into the egg, the first stage of embryogenesis begins - crushing, which is a series of successive mitotic divisions of the zygote. At the same time, with each division, smaller and smaller cells are formed, which are called blastomeres (from the Greek blastos - sprout, meros - part). Crushing of cells occurs due to a decrease in the volume of the cytoplasm. Moreover, the process of cell division continues until the size of the resulting cells is equal to the size of other somatic cells of organisms of this species. As a result, the mass of the embryo in the final period and its volume remain constant and approximately equal to the zygote.

The developed muscular and skeletal systems ensured the movement of organisms, the maintenance of a certain body shape, protection and support for organs. The ability to actively move allowed animals to search for food, find shelter and settle.

Liquid tissue - blood - became such a circulatory transport system. The life cycle of multicellular organisms is a complex individual development, during which an adult organism is formed from a fertilized egg. The fertilized egg is crushed, and the resulting cells differentiate into germ layers and rudiments of organs.

There are two groups of multicellular organisms: radiant (radially symmetrical), or two-layered, and bilaterally symmetrical, or three-layered.

Radiant are characterized by several planes of symmetry and a radial arrangement of organs around the main axis of the body. In the process of individual development, they form only two germ layers - ectoderm and endoderm. The radiant type is intestinal.

Most animals are bilaterally symmetrical. They have one plane of symmetry, which divides their body into two mirror identical halves - left and right. There are three germ layers - endoderm, mesoderm and ectoderm.

According to the presence or absence of an internal skeleton, animals are divided into two groups - invertebrates (all types except Chordates) and vertebrates (Chordates).

Ticket number 22

1. A population is a structural unit of a species. (Textbook of biology, grade 9, section 1, chapter 5, § 10;)

Areas completely inhabited by one or another species do not exist in nature. Within the range, individuals of this species develop only habitats suitable for their life. The degree of filling of the occupied space different types different. But there are always “voids” and accumulations in it. In other words, the range consists of more or less numerous areas where a certain species is found. For example, colonies of the European mole, clearly visible on the mounds of the earth, are located on forest edges and meadows, common spruce grows mainly in lowlands with significantly moistened soil.

Accumulations of individuals of the same species in terms of numbers can be large or small, exist for a long time (centuries or more) or throughout the life of only two or three generations, after which they, as a rule, die from any accidents, for example, diseases, a sharp deterioration in weather conditions and etc. For the fate of a species, a much more important role is played by those groups of individuals that are stably preserved throughout the life of many generations. The number of individuals in such groups can significantly increase under favorable conditions and decrease under unfavorable ones, however, they have a chance of long-term existence in the given territory. Such groupings (aggregations) of individuals of the same species, inhabiting a certain part of the range for a long time, freely interbreeding with each other and producing fertile offspring, relatively isolated from other aggregates of the same species, are called a population (from Latin populus - people, population). Due to the spatial dissociation of populations, the species is adapted to exist in a variety of environmental conditions. Thus, the population is an intraspecific grouping and, consequently, a specific form of existence of the species, and the species itself is a complex biological system.

Characteristics of populations. Each population of any species as a biological system has a certain structure.

The structure of a population is understood as a certain quantitative ratio of individuals that differ in morphological and physiological characteristics, age, sex, the nature of distribution in space and other properties.

The main parameters of a population are, first of all, its abundance and density.

Number - total amount individuals in the population. It is not constant, as the conditions of the habitat of the population are changeable. The population size depends on the ratio of the intensity of reproduction (fertility) and mortality. In the process of reproduction, the population grows, while mortality leads to a decrease in its number. For each population there are upper and lower limits of abundance, which can be measured by studying its seasonal and interannual changes.

Population density is the number of individuals or their biomass per unit area or volume (for example, 150 pine plants per 1 ha; 0.5 cyclops per 1 m 3 of water). Population density is also variable and depends on abundance. With an increase in numbers, the density does not increase only if it is possible to resettle the population and expand its range.

Spatial distribution is the features of the distribution of individuals of the population in the occupied territory. It is determined by the degree of homogeneity of the habitat, the availability of habitable sites, as well as biological features species, the behavior of its individuals. Knowing the type of distribution of organisms allows you to correctly estimate the density by sampling.

Natural populations are characterized by three types of distribution of individuals: random, uniform (regular) and group (aggregated) (Fig. 1.3).

random distribution of individuals is observed in a homogeneous habitat, with a low population size and the absence of the desire of individuals to form groups (for example, in planarians, hydras). In nature, this type of distribution is rare.

Uniform distribution is typical for species characterized by fierce competition between individuals for the same resources and a strong territorial instinct (predatory fish, mammals, birds, spiders).

Aggregated (group) distribution occurs in nature most often. It is expressed in the formation of groups of individuals, between which there are significant uninhabited territories. The reasons for the aggregation of individuals may be the heterogeneity of the environment and the limited habitats suitable for life, the features of reproduction, the desire to live in a group.

The age structure reflects the ratio of different age groups in the population (Fig. 1.4), as well as the seasonal and interannual dynamics of this ratio. Three ecological ages are usually distinguished in a population: pre-reproductive (before breeding), reproductive (during the breeding season), and post-reproductive (after breeding). Under favorable conditions, all age groups are present in the population and a more or less stable level of abundance is maintained. Decreasing populations are dominated by old individuals that are no longer able to reproduce intensively. Such an age structure indicates unfavorable living conditions. The study of the distribution of organisms by age has great importance in predicting the number of populations over the life of a number of next generations. Such studies make it possible to plan, for example, the fishing of fish or fur-bearing animals for a number of years ahead.

The sex structure is formed by the sex ratio in populations with dioecious individuals (see Fig. 1.4). These include most animals and all dioecious plants. The change in the sexual structure of a population is reflected in its role in the ecosystem, since males and females of many species have differences in the nature of nutrition, rhythm of life, and behavior. So, females of some species of mosquitoes, ticks and midges are blood-sucking, while males feed on plant sap or nectar. Fertility characterizes the frequency of the appearance of new individuals in the population due to reproduction.

Mortality (absolute and specific) is the opposite of fertility.

The ratio between the birth and death rates determines the population dynamics. So, if the birth rate is higher than the death rate, then the population will increase, and vice versa, it will decrease if the death rate exceeds the birth rate. In the case of equality of birth and death rates, the population will be maintained at a constant level.

The form of existence of a species is a population - a self-sustaining collection of individuals of the same species, which has its own gene pool. The ability of a population to long-term existence in a particular part of the species range is ensured by its characteristic structure and group properties: abundance, density, sex and age structure, fertility and mortality. The values of these indicators are not constant, which makes it possible for the population to adapt to changing environmental conditions.

2. The concept of systematics. Significance of the works of K. Linnaeus. binary nomenclature. ( Biology textbook, grade 9, section 1, chapter 5, § 10;)

Systematics is that part of zoology and botany that deals with the description and study of organic forms that now live on the earth's surface. Systematics as a science pursues tasks of two kinds: practical and theoretical. The practical task of S. is to distinguish all the breeds (species) of animals and plants that exist on earth, to give each of them a special name and, if possible, an accurate and clear description (diagnosis), which would not allow mixing different species with one another. But this practical side does not exhaust the task of S.

Its theoretical task is to 1) by observing organic forms from the point of view of their constancy or variability, depending on external conditions, geographical distribution, etc., to determine the conditions for changing organisms, i.e., the transition of one form to another; 2) in order, by studying organisms from the point of view of their similarity or difference, to notice between them related features that indicate a common origin, and thus restore their genealogy. The ultimate goal of S. is an explanation of the process of origin of the entire variety of organic forms. The theory of S. is, after all, the theory of evolution. Therefore, S. is often unfairly called a descriptive science. It deserves this name as much as any other science based on positive facts. Method C. To achieve these goals, naturalists arrange the forms of animals and plants in a system, that is, they distribute them according to the degree of similarity into groups, and these latter, in one way or another, arrange them in classes or groups of a higher order.

In practical terms, it is required of a system that every organism occupies a completely definite position in it, in accordance with its characteristics, so that, having met any organism unknown to us, it would be easy to determine its place in the system, thus find out its name, if it has already been described, or make sure that this form has not yet been described by anyone and does not yet have a name. IN theoretically the system should clearly express the degrees of relatedness of organisms and outline, as far as possible, their genealogy. Both in zoology and botany, many systems have been proposed by various scientists. Judging by the extent to which these latter satisfy more practical or theoretical requirements, they are called artificial or natural. The artificial system is not consistent with the natural relationship of organisms; it distributes them simply on the basis of purely arbitrary, but as clear and constant as possible features. Artificial systems used to play an important role in botany, especially the sexual system of Linnaeus, established by him in 1735 and dominating science for almost 100 years. In zoology, strictly speaking, there have never been purely artificial systems, because here the natural similarity of organisms and groups is expressed comparatively much more sharply. As regards to natural system, then it has as its main goal the expression of general similarity, i.e., kinship.

Karl Linnaeus (1707-1778), Swedish naturalist, creator of the system of flora and fauna, the first president of the Swedish Academy of Sciences (from 1739), a foreign honorary member of the St. Petersburg Academy of Sciences (1754). For the first time he consistently applied binary nomenclature and built the most successful artificial classification of plants and animals, described approx. 1500 plant species. He advocated the permanence of species and creationism. Author of "The System of Nature" (1735), "Philosophy of Botany" (1751), etc.

binary, or binomial nomenclature - a method of designating species adopted in biological systematics using a two-word name (binomen), consisting of a combination of two names (names): the name of the genus and the name of the species (according to the terminology adopted in zoological nomenclature) or the name of the genus and the specific epithet (according to botanical terminology).

The name of the genus is always written with a capital letter, the name of the species (specific epithet) is always with a small letter (even if it comes from a proper name). In the text, the binomen is usually written in italics. The species name (specific epithet) should not be given separately from the genus name, since without the genus name it is meaningless. In some cases, the genus name can be shortened to a single letter or a standard abbreviation.

According to the tradition established in Russia, the phrase binomial nomenclature (from the English binomial) has become widespread in the zoological literature, and in the botanical literature - binary, or binomial nomenclature (from the Latin binominalis).

Rosacanina L. - dog rose (rose hip) (Linnaeus)

Ticket number 23

1. Driving forces of evolution(Textbook of biology, grade 9, section 1, chapter 3, §5)

In Darwin's evolutionary theory, the prerequisite for evolution is hereditary variability, and the driving forces of evolution are the struggle for existence and natural selection. When creating the evolutionary theory, Ch. Darwin repeatedly refers to the results of breeding practice. He showed that the diversity of varieties and breeds is based on variability. Variability is the process of the emergence of differences in descendants compared to ancestors, which determine the diversity of individuals within a variety or breed. Darwin believes that the causes of variability are the impact on organisms of environmental factors (direct and indirect), as well as the nature of the organisms themselves (since each of them reacts specifically to the impact of the external environment). Darwin, analyzing the forms of variability, singled out three among them: definite, indefinite and correlative.

A certain, or group, variability is a variability that occurs under the influence of some environmental factor that acts equally on all individuals of a variety or breed and changes in a certain direction. Examples of such variability are an increase in body weight in animal individuals with good feeding, a change in the hairline under the influence of climate, etc. A certain variability is massive, covers the entire generation and is expressed in each individual in a similar way. It is non-hereditary, that is, in the descendants of the modified group, under other conditions, the traits acquired by the parents are not inherited.

Indefinite, or individual, variability manifests itself specifically in each individual, that is, it is single, individual in nature. It is associated with differences in individuals of the same variety or breed under similar conditions. This form of variability is indefinite, i.e., a trait under the same conditions can change in different directions. For example, in one variety of plants, specimens appear with different colors of flowers, different intensity of color of petals, etc. The reason for this phenomenon was unknown to Darwin. Indefinite variability is hereditary, that is, it is stably transmitted to offspring. This is her importance for evolution. Darwin comes to the conclusion that only heritable changes are important for the evolutionary process, since only they can accumulate from generation to generation. According to Darwin, the main factors in the evolution of cultural forms are hereditary variability and human selection (Darwin called such selection artificial). Variability is a necessary prerequisite for artificial selection, but it does not determine the formation of new breeds and varieties.

Darwin considered the explanation of the historical variability of species possible only through the disclosure of the causes of adaptability to certain conditions. He came to the conclusion that the adaptability of natural species, as well as cultural forms, is the result of selection, which was carried out not by man, but by environmental conditions.

How is natural selection carried out? One of its most important conditions in the natural environment, Darwin considers the overpopulation of species, which occurs as a result of a geometric progression of reproduction. Darwin drew attention to the fact that individuals of species that give even relatively small real offspring eventually reproduce quite intensively. For example, ascaris produces up to 200 thousand eggs per day, the female perch spawns 200-300 thousand eggs, and cod - up to 10 million eggs.

Overpopulation is the main (although not the only) cause of the struggle for existence between organisms. In the concept of "struggle for existence" he puts a broad and metaphorical meaning.

The struggle of organisms occurs both among themselves and with the physico-chemical conditions of the environment. It has the character of direct collisions between organisms or, more often, indirect conflicts. Competing organisms may not even come into contact with each other and still be in a state of fierce struggle (for example, spruce and acid growing under it).

The natural result of the contradictions between organisms and the external environment is the extermination of a part of the individuals of the species (elimination). The struggle for existence is thus the eliminating factor.

The scheme of action of natural selection in the species system according to Darwin is as follows:

Variability is inherent in any group of animals and plants, and organisms differ from each other in many ways.

The number of organisms of each species that are born into the world exceeds the number of those that can find food and survive. However, since the abundance of each species is constant under natural conditions, it should be assumed that most of the offspring perish. If all the descendants of any one species survived and multiplied, they would very soon outcompete all other species on the globe.

Since more individuals are born than can survive, there is a struggle for existence, competition for food and habitat. This may be an active life-and-death struggle, or less obvious, but no less effective competition, as, for example, for plants during a period of drought or cold.

Among the many changes observed in living beings, some make it easier to survive in the struggle for existence, while others lead to the fact that their owners die. The concept of "survival of the fittest" is the core of the theory of natural selection.

Surviving individuals give rise to the next generation, and in this way "fortunate" changes are transmitted to subsequent generations. As a result, each next generation is more adapted to the environment; as the environment changes, further adaptations occur. If natural selection has been operating for many years, then the last offspring may turn out to be so dissimilar to their ancestors that it would be advisable to single them out as an independent species.

It may also happen that some members of a given group of individuals will acquire some changes and be adapted to the environment in one way, while other members of it, having a different set of changes, will be adapted in a different way; in this way, two or more species may arise from one ancestral species, provided that such groups are isolated.

The emergence of multicellularity was the most important stage in the evolution of the entire animal kingdom. The dimensions of the body of animals, previously limited to one cell, in multicellular organisms increase significantly due to an increase in the number of cells. The body of multicellular organisms consists of several layers of cells, at least two. Among the cells that form the body of multicellular animals, there is a separation of functions. Cells differentiate into integumentary, muscular, nervous, glandular, sex, etc. In most multicellular complexes of cells that perform the same functions, they form the corresponding tissues: epithelial, connective, muscle, nerve, and blood. The tissues, in turn, form complex organs and organ systems that provide the vital functions of the animal.

Multicellularity greatly expanded the possibilities of the evolutionary development of animals and contributed to the conquest of all possible habitats by them.

Everything multicellular animals reproduce sexually. Sex cells - gametes - are formed in them very similarly, by cell division - meiosis - which leads to a reduction, or reduction, in the number of chromosomes.

For all multicellular organisms, a certain life cycle is characteristic: a fertilized diploid egg - a zygote - begins to split up and gives rise to a multicellular organism. When the latter matures, sex haploid cells - gametes are formed in it: female - large eggs or male - very small spermatozoa. The fusion of an egg with a sperm cell is fertilization, as a result of which a diploid zygote, or a fertilized egg, is formed again.

Modifications of this main cycle in some groups of multicellular organisms can occur a second time in the form of alternation of generations (sexual and asexual), or replacement of the sexual process by parthenogenesis, i.e., sexual reproduction, but without fertilization.
Asexual reproduction, so characteristic of the vast majority of unicellular organisms, is also characteristic of the lower groups of multicellular organisms (sponges, coelenterates, flat and annelids, and partly echinoderms). Very close to asexual reproduction is the ability to restore lost parts, called regeneration. It is inherent to one degree or another in many groups of both lower and higher multicellular animals that are not capable of asexual reproduction.

Sexual reproduction of multicellular animals

All cells of the body of multicellular animals are divided into somatic and sexual. Somatic cells (all body cells, except sex cells) are diploid, that is, all chromosomes are represented in them by pairs of similar homologous chromosomes. Sex cells have only a single, or haploid, set of chromosomes.

Sexual reproduction of multicellular organisms occurs with the help of germ cells: the female egg, or egg, and the male germ cell, the sperm. The process of fusion of the egg and sperm is called fertilization, resulting in a diploid zygote. A fertilized egg receives from each parent a single set of chromosomes, which again form homologous pairs.

From a fertilized egg, by its repeated division, a new organism develops. All cells of this organism, except for the sex cells, contain the initial diploid number of chromosomes, the same as those of its parents. The preservation of the number and individuality of chromosomes (karyotype) characteristic of each type is ensured by the process of cell division - mitosis.

Sex cells are formed as a result of a special modified cell division called meiosis. Meiosis results in the reduction, or halving, of the number of chromosomes through two successive cell divisions. Meiosis, like mitosis, proceeds very similarly in all multicellular organisms, in contrast to unicellular organisms, in which these processes vary greatly.

In meiosis, as in mitosis, the main stages of division are distinguished: prophase, metaphase, anaphase and telophase. The prophase of the first division of meiosis (prophase I) is very complex and the longest. It is divided into five stages. In this case, paired homologous chromosomes, obtained one from the maternal and the other from the paternal organism, are closely connected or conjugated with each other. The conjugating chromosomes thicken, and at the same time it becomes noticeable that each of them consists of two sister chromatids connected by a centromere, and together they form a quadruple of chromatids, or a tetrad. During conjugation, chromatid breaks and the exchange of identical sections of homologous, but not sister chromatids from the same tetrad (from a pair of homologous chromosomes) can occur. This process is called chromosome crossing or crossing over. It leads to the formation of compound (mixed) chromatids containing segments obtained from both homologues, and therefore from both parents. At the end of prophase I, homologous chromosomes line up in the plane of the cell equator, and achromatin spindle filaments are attached to their centromeres (metaphase I). The centromeres of both homologous chromosomes repel each other and move to different poles of the cell (anaphase I, telophase I), which leads to a reduction in the number of chromosomes. Thus, only one chromosome from each pair of homologues enters each cell. The resulting cells contain half, or haploid, the number of chromosomes.

After the first division of meiosis, the second usually follows almost immediately. The phase between these two divisions is called interkinesis. The second division of meiosis (II) is very similar to mitosis, with a greatly shortened prophase. Each chromosome consists of two chromatids held together by a centromere. In metaphase II, the chromosomes line up in the equatorial plane. In anaphase II, the division of the centromeres occurs, after which the spindle threads pull them apart to the division poles, and each chromatid becomes a chromosome. Thus, four haploid cells are formed from one diploid cell during meiosis. In the male body, spermatozoa are formed from all cells; in the female, only one of the four cells turns into an egg, and three (small polar bodies) degenerate. The complex processes of gametogenesis (spermato- and oogenesis) in all multicellular organisms are very similar.

sex cells

In all multicellular animals, germ cells are differentiated into large, usually immobile female cells - eggs - and very small, more often mobile male cells - spermatozoa.

The female sex cell - an egg - is most often spherical, and sometimes more or less elongated. The egg cell is characterized by the presence of a significant amount of cytoplasm, in which a large bubble-shaped nucleus is placed. Outside, the egg is dressed in more or less shells. The egg cells in most animals are the largest cells in the body. However, their sizes are not the same in different animals, which depends on the amount of nutritious yolk. There are four main types of egg structure: alecithal, homolecital, telolecital and centrolecital eggs.

Alecithal eggs are almost devoid of yolk or contain very little of it. Alecithal eggs are very small, they are characteristic of some flatworms and mammals.

Homolecithal, or isolecithal, eggs contain relatively little yolk, which is distributed more or less evenly in the cytoplasm of the egg. The nucleus occupies an almost central position in them. Such are the eggs of many mollusks, echinoderms, etc. However, some homolecithal eggs have a large amount of yolk (hydra eggs, etc.).

Telolecital eggs always contain a large amount of yolk, which is very unevenly distributed in the cytoplasm of the egg. Most of the yolk is concentrated at one pole of the egg, called the vegetative pole, while the nucleus is shifted to a greater or lesser extent towards the opposite pole, called the animal pole. Such eggs are characteristic of various groups of animals. Telolecital eggs reach the largest sizes, and depending on the degree of loading with yolk, their polarity is expressed to varying degrees. Typical examples of telolecithal eggs are the eggs of frogs, fish, reptiles and birds, and of invertebrates, the eggs of cephalopods.

However, polarity is inherent not only in telolecithal eggs, but also in all other types of eggs, i.e. they also have differences in the structure of the animal and vegetative poles. In addition to the indicated increase in the amount of yolk at the vegetative pole, polarity can manifest itself in an uneven distribution of cytoplasmic inclusions, egg pigmentation, etc. There is evidence of differentiation of the cytoplasm at the animal and vegetative poles of the egg.

Centrolecithal eggs are also very rich in yolk, but it is evenly distributed throughout the egg. The nucleus is placed in the center of the egg, it is surrounded by a very thin layer of cytoplasm, the same layer of cytoplasm covers the entire egg near its surface. This peripheral layer of cytoplasm communicates with the perinuclear plasma using thin cytoplasmic filaments. Centrolecithal eggs are characteristic of many arthropods, in particular all insects.

All eggs are covered with the thinnest plasma membrane, or plasmalemma. In addition, almost all eggs are surrounded by another, the so-called yolk membrane. It is formed in the ovary, and it is called the primary membrane. Eggs can also be dressed with secondary and tertiary shells.

The secondary shell, or chorion, of the eggs is formed by the ovarian follicular cells surrounding the egg. The best example is the outer shell - chorion - of insect eggs, consisting of solid chitin and equipped with a hole at the animal pole - micropyle, through which spermatozoa penetrate.

Tertiary membranes, which usually have a protective value, develop from the secretions of the oviducts or accessory (shell) glands. Such, for example, are the shells of eggs of flatworms, cephalopods, gelatinous shells of gastropods, frogs, etc.

Male germ cells - spermatozoa - unlike egg cells, are very small, their sizes range from 3 to 10 microns. Spermatozoa have a very small amount of cytoplasm, their main mass is the nucleus. Due to the cytoplasm, spermatozoa develop adaptations for movement. The shape and structure of spermatozoa of various animals are extremely diverse, but the most common is the form with a long flagella-like tail. Such a spermatozoon consists of four sections: the head, neck, connecting part and tail.

The head is almost entirely formed by the nucleus of the sperm, it carries a large body - the centrosome, which helps the penetration of the sperm into the egg. Centrioles are located on its border with the neck. From the neck, the axial thread of the spermatozoon originates, passing through its tail. According to electron microscopy, its structure turned out to be very close to that of flagella: two filaments in the center and nine along the periphery of the axial filament. In the central part, the axial filament is surrounded by mitochondria, which represent the main energy center of the spermatozoon.

Fertilization

In many invertebrates, fertilization is external and occurs in water, while in others, internal fertilization takes place.

The process of fertilization consists in the penetration of spermatozoa into the egg and in the formation of one fertilized egg from two cells.

This process occurs differently in different animals, depending on the presence of micropyle, the nature of the membranes, etc.

In some animals, as a rule, one spermatozoon penetrates the egg, and at the same time, due to the yolk membrane of the egg, a fertilization membrane is formed that prevents the penetration of other spermatozoa.

In many animals, a larger number of spermatozoa penetrate the egg (many fish, reptiles, etc.), although only one takes part in fertilization (in fusion with the egg cell).

During fertilization, the hereditary characteristics of two individuals are combined, which ensures greater viability and greater variability of the offspring, and, consequently, the possibility of the appearance of useful adaptations to various living conditions.

Embryonic development of multicellular animals

The whole process, from the beginning of the development of a fertilized egg to the beginning of the independent existence of a new organism outside the mother's body (during live birth) or after it leaves the egg shells (during oviparity), is called embryonic development.

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« general characteristics and classification of the subkingdom of multicellular organisms. Diversity and classification of coelenterates.»

To reveal the main features of the structure and life of multicellular organisms.

To get acquainted with the features of the structure of multicellular organisms;

Continue the formation of the concept of the habitat of multicellular organisms;

To study the systematics of multicellular organisms and the features of their vital activity;

Give an idea of the general characteristics and classification of coelenterates.

Bring up cognitive interest to the animal world;

Formation of a scientific-materialistic worldview based on the relationship between the similarity of unicellular and multicellular organisms.

Development of the ability to work with textbook material;

The development of logical thinking through the ability to analyze, summarize materials, compare, draw conclusions.

Expand the circle of knowledge about the features of the multicellular subkingdom.

Verbal: story, explanation, conversation.

Visual: demonstration of visual aids.

Lesson steps:

Organizational moment (1 min)

Testing knowledge on the topic "Subkingdom unicellular, general characteristics and systematics." (15 min)

Learning new material (20 min)

General characteristics of multicellular organisms.

Features of the structure and their vital activity.

Classification of multicellular organisms.

Consolidation and generalization of the material (5-10 min)

Homework(1 min)

During the classes:

Organizing time.

Hello guys! Sit down.

Checking knowledge on the topic " General characteristics and classification of the multicellular subkingdom. Diversity and classification of coelenterates»

Guys, in the last lesson, you studied the topic " Subkingdom unicellular, general characteristics and systematics. Now we will check how you have learned the material covered. We close all textbooks and notebooks. We take out the sheets and sign them. You have 10 minutes to complete the task. Let's get started.

Learning new material

Guys, you already know who unicellular organisms are, but do you remember who multicellular organisms are?

Multicellular organisms are organisms whose bodies are made up of many cells.

What are the two types of subkingdom multicellular?

Multicellular organisms are divided into vertebrates and invertebrates.

Why are animals called vertebrates? Why invertebrates?

Invertebrates - no internal skeleton and spine.

Vertebrates - there is a notochord in embryonic development, and later turns into a spine.

Multicellular animals are extremely diverse in structure, features of life activity, different in size, body weight, etc. On the basis of the most essential general structural features, they are divided into 14 types.

The subkingdom Multicellular is divided into 2 divisions: Parazoa (primitive multicellular) and Eumetazoa (true multicellular).

primitive metazoans are aquatic animals. They lead an attached lifestyle, are filter feeders, receive food along with the flow of water. Like the simplest, these organisms are characterized by intracellular and parietal digestion.

The supersection of primitive metazoans consists of two types: Spongiata and Archaeocyathi.

The sponge type includes marine and freshwater attached multicellular organisms, the skeleton of which consists of simple or differently interconnected needles - spicules.

Sponges are filter feeders. Their body is permeated with numerous channels, opening from the inside and outside with pores.

The type of sponges is divided into 3 classes: Sponges (Spongia) - the most common and numerous, Sclerospongia (Sclerospongia) and Sphinctozoa (Sphinctozoa). Sometimes this type includes the Receptaculita class, the position of which has an unclear systematic position.

Sponges are marine and freshwater, solitary and colonial organisms that do not have separate tissues and organs.

Sponges are spherical, mushroom-shaped, cylindrical or cup-shaped. Sometimes they form lumpy or cushion-like outgrowths on a hard substrate. The sizes of the sponges range from a few millimeters to 1.5 meters.

Sponges lead an attached lifestyle, but can freely lie or burrow (drillers). Sponges feed and breathe as water passes through their body. The main feature of sponges is the presence of a penetrating system of channels in their body.

The skeleton of sponges is represented by thin needles - spicules - having different sizes, shapes and composition. The composition of the skeleton is mineral, organic or mixed. The mineral skeleton may be calcareous or siliceous. The form of mineral spicules is one-, three-, four- and multiaxial.

And now let's move on to the general characteristics of their intestinal classification.

The name coelenterates comes from two-layer organisms with a single body cavity - intestinal. Intestinal - the most low-organized multicellular solitary or colonial animals. Many have a calcareous skeleton; some are organic.

Coelenterates reproduce sexually and asexually, with the sexual generation (jellyfish) being free-swimming organisms, the asexual (polyps) leading an attached lifestyle.

The coelenterates include hydroid and coral polyps, sea anemones, hydras, jellyfish.

Most coelenterates live in the seas and oceans. They unite about 9 thousand species, which are divided into 3 classes: hydro-like (hydroid), scyphoid (cup-shaped) and coral polyps.

The body of coelenterates often has radial symmetry.

Guys, what does ray symmetry mean?

Radial (radial) symmetry- a form of symmetry in which a body (or figure) coincides with itself when an object rotates around a certain point or line

Now let's look directly at the classification of intestinal, and their prominent representatives.

In the class hydroid (Hydrozoa) polyps dominate, usually forming a branched colony by budding from a huge number of individuals - hydrants. From polyps, jellyfish bud, which, as a rule, do not live long; some species do not form jellyfish.

6-7 hydroid orders are divided into 4000 species, found mainly in the seas. Most live in the littoral, only a few hydromedusas are deep-sea forms. Some hydroids (gonionema, Portuguese boat) cause severe burns that are dangerous to humans.

Hydra- a characteristic representative of freshwater polyps - lives in lakes, ponds and rivers. The cylindrical body is attached to the substrate by the sole; at the opposite end there is a mouth surrounded by tentacles. Fertilization is internal. Interstitial cells located in the ectoderm contribute to the regeneration of damaged tissues. Hydra can be cut into pieces, even turned inside out - it will still live and grow. Hydra is painted green or brown; body length is from 5 mm to 1 cm. Its life span is only one year.

Scyphozoa (Scyphozoa), on the contrary, they are distinguished by free-swimming jellyfish, the size of which ranges from a few millimeters to 2–3 m (cyanoea); cyanide tentacles stretch up to 20 m in length. The polyp is poorly developed, sometimes it is not at all. The intestinal cavity is divided by incomplete partitions into chambers. Scyphomedusa live for several months.

About 200 species in temperate and tropical waters of the World Ocean. Some species (cornerots, aurelia) are eaten in a salty form. Many jellyfish cause severe redness and burns when touched. The Australian scyphomedusa hirodrofus can cause fatal burns in humans.

Coral polyps (Anthozoa)- colonial (rarely solitary) marine organisms. A body with a length of several millimeters to one meter has six-beam or eight-beam symmetry. Due to the fact that fertilization in corals is internal, the planula larva develops in the intestinal cavity of the polyp that forms the eggs. There is no medusa stage. The mouth opening is connected to the intestinal cavity by the pharynx. The polyps of one colony have a common intestinal cavity, and the food obtained by one of the polyps becomes the property of the entire colony. About 6000 species of coral polyps live in all seas with fairly high salinity; in the northern and Far Eastern seas of Russia there are about 150 species.

Some colonial polyps (for example, stony corals) surround themselves with a massive calcareous skeleton. When a polyp dies, its skeleton remains. Polyp colonies, growing over thousands of years, form coral reefs and entire islands. The largest of them - the Great Barrier Reef - stretches along the eastern coast of Australia for 2300 km; its width is from 2 to 150 km. Reefs in their places of distribution (in warm and salty waters with a temperature of 20-23 ° C) are a serious obstacle to navigation. Branches of coral are used as decorations.

Coral reefs are unique ecosystems in which a huge number of other animals find shelter: mollusks, worms, echinoderms, fish. During the Ice Age, coral reefs fringed many of the islands. Then the sea level began to rise, and the polyps built up their reefs at an average rate of a centimeter a year. Gradually, the island itself was hidden under water, and in its place a shallow lagoon formed, surrounded by reefs. The wind brought the seeds of plants to them. Then animals appeared, and the island turned into a coral atoll.

General signs of the structure and life of representatives of the Sponge type

Sexual reproduction of multicellular animals

sex cells

Fertilization

Embryonic development of multicellular animals

ecosystems

Zoology

Biology

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