1. What properties unite all cells of organisms?
All cells of living organisms have all the characteristics of a living organism: movement, metabolism, growth, development, self-reproduction, self-regulation, etc.
2. What are the main components of any cell?
The essential components of a living cell are the plasma membrane, the cytoplasm and the genetic apparatus responsible for the implementation of hereditary information in the cell. Other cellular components differ in different groups organisms.
3. What are the main provisions of modern cell theory?
The main provisions of modern cell theory:
1) The cell is a universal structural and functional unit of the living.
2) All cells have a similar structure, chemical composition and general principles of life.
3) Cells are formed only when the original cells divide.
4) Cells are capable of independent life, but in multicellular organisms their work is coordinated, and the body is an integral system.
5) It is thanks to the activity of cells in multicellular organisms that metabolism and energy, growth and reproduction are carried out
4. What was the significance of the cell theory for the development of biology?
Thanks to the formation of the cell theory, it became clear that the cell is the most important component of living organisms. That all biochemical and physiological processes in the body occur at the cellular level. cell theory made it possible to draw a conclusion about the similarity chemical composition all cells, general plan their structure, which confirms the phylogenetic unity of the entire living world.
Compare the provisions of the cell theory formulated by M. Schleiden and T. Schwann with modern ones. How did the development of biology influence the formulation of cell theory?
Thanks to the development of biology and the emergence of new research methods, the cellular theory has been supplemented and refined. So Schwann and Schleiden considered the cell to be the smallest unit of the living, but now it has been established that there are smaller structures (organelles) that are part of the cell. Also, the theory was supplemented with points about the similarity of cells of various organisms in structure, chemical composition and general principles of life.
Think:
What has held back the development of cell theory since the beginning of the study of the cell?
The first steps in the study of the cell were made with the help of a light microscope. With the further development of the microscope and other tools for studying the cell, the amount of knowledge about the cell has increased. The use of an electron microscope made it possible to study in detail all the structural components of the cell (organelles). From this we can conclude that the limiting factor for the development of cytology long time was the level of development of research tools, in particular the microscope.
Cytology is the science of the cell. The history of the study of the cell is associated with the names of such scientists as Robert Hooke, Anthony van Leeuwenhoek, Mattis Schleiden and Theodor Schwann. Robert Hooke coined the term "cell" in 1665. He was the first to use a microscope to study tissues, and on a cut of cork and elderberry core he saw cells, which he called cells. Anthony van Leeuwenhoek first discovered the microcosm in 1674, for which he used light microscopy to see cells under a magnification of 270 times. In 1831, R. Brown discovered the nucleus. Mattis Schleiden and Theodor Schwann in 1839 create the cell theory. In the work "Microscopic studies on the correspondence in the structure and growth of animals and plants" (1839), T. Schwann formulated the main provisions of the cell theory, which were then repeatedly supplemented and refined.
Modern cell theory includes the following provisions:
1. All living organisms are made up of cells. A cell is a structural, functional unit of the living, the basic unit of the structure and development of all living organisms, the smallest unit of the living;
2. Cells of all unicellular and multicellular organisms similar (homologous) in their structure, chemical composition, basic manifestations of vital activity and metabolism.
3. Reproduction of cells occurs through their division, and each new cage formed as a result of division of the original (mother) cell.
4. In complex multicellular organisms, cells are specialized in their functions and form tissues; tissues consist of organs that are closely interconnected and subordinate to the nervous and humoral systems of regulation.
5. The cellular structure of organisms is evidence that all living organisms have a single origin.
The significance of the cell theory in the development of science lies in the fact that thanks to it it became clear that the cell is the most important component of all living organisms. It is their main "building" component, the cell is the embryonic basis of a multicellular organism, because The development of an organism begins with a single cell, the zygote. The cell is the basis of physiological and biochemical processes in the body, because Ultimately, all physiological and biochemical processes take place at the cellular level. The cell theory made it possible to come to the conclusion that the chemical composition of all cells is similar and once again confirmed the unity of everything. organic world.
All living organisms are made up of cells - from one cell (protozoa) or many (multicellular). A cell is one of the main structural, functional and reproducing elements of living matter; it is an elementary living system. There are evolutionarily non-cellular organisms (viruses), but they can only reproduce in cells. Various cells differ from each other both in structure and size (cell sizes range from 1 μm to several centimeters - these are the eggs of fish and birds), and in shape (they can be round like erythrocytes, tree-like like neurons), and in biochemical characteristics (for example, in cells containing chlorofall or bacteriochlorophyll, photosynthesis processes take place, which are impossible in the absence of these pigments), and by function (there are sex cells - gametes and somatic - body cells, which in turn are divided into many different types).
Cell study methods:
1. Differential-centrifugation (organelles of different density fall out in layers in a centrifuge).
2. The method of labeled atoms (when studying biochemical processes, a radioactive label is introduced into a substance, which signals with radioactive radiation).
3. Microscopy (light, electron microscopes).
All living organisms are made up of cells - from one cell (single-celled organisms) or many (multicellular). A cell is one of the main structural, functional and reproducing elements of living matter; it is an elementary living system. There are non-cellular organisms (viruses), but they can only reproduce in cells. There are organisms that have secondarily lost cellular structure(some algae). The history of the study of the cell is associated with the names of a number of scientists. R. Hooke was the first to use a microscope to study tissues and on a cut of a cork and an elderberry core he saw cells, which he called cells. Anthony van Leeuwenhoek first saw cells under 270x magnification. M. Schleiden and T. Schwann were the creators of the cell theory. They mistakenly believed that the cells in the body arise from the primary non-cellular substance. Later, R. Virchow formulated one of the most important provisions of the cellular theory: "Every cell comes from another cell ..." The significance of the cellular theory in the development of science is great. It became obvious that the cell is the most important component of all living organisms. It is their main component morphologically; the cell is the embryonic basis of a multicellular organism, because the development of an organism begins with a single cell - a zygote; cell - the basis of physiological and biochemical processes in the body. The cell theory made it possible to conclude that the chemical composition of all cells is similar and once again confirmed the unity of the entire organic world.
Modern cell theory includes the following provisions:
The cell is the basic unit of the structure and development of all living organisms, the smallest unit of the living;
The cells of all unicellular and multicellular organisms are similar (homologous) in their structure, chemical composition, basic manifestations of vital activity and metabolism;
Reproduction of cells occurs by their division, and each new cell is formed as a result of the division of the original (mother) cell;
In complex multicellular organisms, cells are specialized in their function and form tissues; tissues consist of organs that are closely interconnected and subordinate to the nervous and humoral systems of regulation.
Significance of cell theory in the development of science lies in the fact that thanks to it it became clear that the cell is the most important component of all living organisms. It is their main "building" component, the cell is the embryonic basis of a multicellular organism, because The development of an organism begins with a single cell, the zygote. The cell is the basis of physiological and biochemical processes in the body, because Ultimately, all physiological and biochemical processes take place at the cellular level. The cell theory made it possible to come to the conclusion that the chemical composition of all cells is similar and once again confirmed the unity of the entire organic world. All living organisms are made up of cells - from one cell (protozoa) or many (multicellular). A cell is one of the main structural, functional and reproducing elements of living matter; it is an elementary living system. There are evolutionarily non-cellular organisms (viruses), but they can only reproduce in cells. Different cells differ from each other both in structure and size (cell sizes range from 1 μm to several centimeters - these are the eggs of fish and birds), and in shape (they can be round like erythrocytes, tree-like like neurons), and in biochemical characteristics ( for example, in cells containing chlorofall or bacteriochlorophyll, photosynthesis processes take place that are impossible in the absence of these pigments), and by function (there are sex cells - gametes and somatic - body cells, which in turn are divided into many different types).
8. Hypotheses of the origin of eukaryotic cells: symbiotic, invagination, cloning. Most popular at present symbiotic hypothesis origin of eukaryotic cells, according to which the basis, or host cell, in the evolution of a cell of the eukaryotic type was an anaerobic prokaryote, capable only of amoeboid movement. The transition to aerobic respiration is associated with the presence of mitochondria in the cell, which occurred through changes in symbionts - aerobic bacteria that penetrated into the host cell and coexisted with it.
A similar origin is suggested for flagella, the ancestors of which were bacterial symbionts that had a flagellum and resembled modern spirochetes. The acquisition by the cell of flagella, along with the development of an active mode of locomotion, had an important consequence of a general order. It is assumed that the basal bodies, which are supplied with flagella, could evolve into centrioles during the emergence of the mechanism of mitosis.
The ability of green plants to photosynthesis is due to the presence of chloroplasts in their cells. Supporters of the symbiotic hypothesis believe that prokaryotic blue-green algae served as symbionts of the host cell that gave rise to chloroplasts.
A strong argument in favor symbiotic The origin of mitochondria, centrioles and chloroplasts is that these organelles have their own DNA. At the same time, the proteins bacillin and tubulin, which make up flagella and cilia, respectively, of modern prokaryotes and eukaryotes, have a different structure.
Central and difficult to answer is the question of the origin of the nucleus. It is believed that it could also be formed from a prokaryotic symbiont. The increase in the amount of nuclear DNA, many times greater than in the modern eukaryotic cell, its amount in the mitochondria or chloroplast, apparently occurred gradually by moving groups of genes from the genomes of symbionts. It cannot be ruled out, however, that the nuclear genome was formed by extending the genome of the host cell (without the participation of symbionts).
According to invagination hypothesis, the ancestral form of the eukaryotic cell was the aerobic prokaryote. Inside such a host cell, several genomes were located simultaneously, initially attached to the cell membrane. Organelles with DNA, as well as a nucleus, arose by invagination and lacing of sections of the membrane, followed by functional specialization into the nucleus, mitochondria, and chloroplasts. In the process of further evolution, the nuclear genome became more complex, and a system of cytoplasmic membranes appeared.
Invagination hypothesis well explains the presence in the shells of the nucleus, mitochondria, chloroplasts, two membranes. However, it cannot answer the question why protein biosynthesis in chloroplasts and mitochondria corresponds in detail to that in modern prokaryotic cells, but differs from protein biosynthesis in the cytoplasm of a eukaryotic cell.
Cloning. In biology, a method of obtaining several identical organisms through asexual (including vegetative) reproduction. This is how, for millions of years, many species of plants and some animals reproduce in nature. However, the term "cloning" is now usually used in a narrower sense and means copying cells, genes, antibodies, and even multicellular organisms in the laboratory. resulting asexual reproduction specimens are, by definition, genetically the same, however, they can also observe hereditary variability due to random mutations or created artificially by laboratory methods. The term "clone" as such comes from the Greek word "klon", which means - twig, shoot, stalk, and is related primarily to vegetative propagation. Cloning plants from cuttings, buds or tubers in agriculture known for thousands of years. During vegetative reproduction and during cloning, genes are not distributed among the descendants, as in the case of sexual reproduction, but are preserved in their entirety. Only animals are different. As animal cells grow, their specialization occurs, that is, the cells lose the ability to realize all the genetic information embedded in the nucleus of many generations.
The development of bird embryos occurs in two stages. The first stage - initial - in the genital tract of the mother and the second - final - outside the mother's body, in the external environment.
During mating, the male's sperm enter the funnel through the oviduct, where the egg is fertilized. After this, the fragmentation of the germinal disk begins. Cleavage grooves form on the yolk (the first - 4-5 hours after ovulation, and the second - 20-25 hours after the first). The grooves are located parallel to the surface of the yolk, forming a blastodisc, its cells, separating from the yolk, form a subembryonic cavity filled with fluid. From the cell of the blastoderm, the outer germinal layer (ectoderm) is first formed, from which the inner germinal layer (endoderm) then exfoliates. The central part of the germinal egg of the cell is located in one layer, and there are a large number of them along the edges. A dark yolk is visible through the central light part of the cell.
The germinal disc is in this state at the time of laying the egg by the laying hen. The whole process of development of the embryo in the oviduct occurs within 24-27 hours, at a mother's body temperature of 40.5-41 ° C, under conditions that completely exclude water evaporation. When an egg enters the external environment, it begins to cool, water evaporates from it. Egg development slows down.
If the egg is not fertilized, the cleavage process does not occur, and the germinal disc looks like a white flat spot. Further development of the embryo resumes when it enters an external environment favorable for growth: under a hen or in an incubator.
Under the influence of heat, the embryo continues to develop. In the first 12 hours of incubation, a third, mesoderm, appears between the two germ layers. From them, tissues and organs of the bird are formed.
The outer leaf is involved in the formation of the nervous system, skin, feather, claws, and the inner leaf is involved in the lungs, digestive tract, endocrine glands, and liver. Cartilage, bones, muscles, reproductive, circulatory and vascular systems will appear from the middle layer. Moreover, circulatory, nervous, excretory system, sense organs are laid in the first 48 hours of incubation.
By the end of the first day of incubation, a notochord is formed in the chicken embryo - a temporary spinal ridge of the embryo with the rudiments of the central nervous system. Then, neural folds appear above the chord along the head process, which eventually turn into a neural tube. Along the chord (to the right and left of the neural tube), paired somite segments (primary vertebrae) appear in the form of square plates. The amnion begins to form (one of the shells of the embryo).
On the second day, yolk veins appear, blood vessels, the rudiments of the organs of vision, hearing, some sections of the intestine and allantois (another embryonic membrane involved in the respiration of the embryo and serving as a place for accumulation of secretions), the heart of the embryo is laid and begins to contract.
On the third day, yolk arteries appear, full cycle blood circulation, the rudiments of the liver, endocrine glands, legs and wings, the folds of the amnion are closed.
On the fourth day, the separation of the embryo from the yolk ends - it turns on its left side, an intestinal tube is formed. The embryo reaches a size of 0.8 cm.
On the fifth day, the thymus gland, stomach are laid, the makings of the skeleton appear. Allantois reaches the boundaries of the air chamber. The length of the embryo exceeds 1 cm.
On the sixth day, the beak begins to form. Allantois reaches the shell. Circulatory system is included in respiration with the absorption of oxygen from the external environment. The toes and wings are separated. The embryo grows up to 1.5 cm.
The seventh day is completely spent on sex differentiation.
From the eighth day, the ossification of the skeleton begins, the beginnings of feathers appear, the kidneys begin to work.
On the ninth day, keratinization of the beak occurs.
The eleventh day is a milestone in development. Allantois covers the entire contents of the egg and closes at the sharp end. Claws appear. Permanent kidneys are included in the work. The embryo reached 3.6 cm.
On the twelfth day, rudiments of feathers appear along the back and tail, the eyelids begin to cover the cornea, forming an oval open hole.
On the thirteenth day, the fluff covers the entire body, the claws become completely horny by the 15th day.
On the nineteenth day, the allantois begins to atrophy and the yolk sac begins to retract. Eyes open.
On the twentieth day, the yolk sac is completely retracted into the abdominal cavity. The umbilical ring closes. Pulmonary breathing and pecking of the shell begins. Having pecked, the chick makes circular movements of the head counterclockwise around the longitudinal axis at the blunt end of the egg.
Having broken the shell membranes, the chicken tries to unbend, resting its head and neck against the shell of the blunt end, and with its legs against the shell of the sharp end. The shell breaks in two and the chick comes out.
fetal membranes: yolk sac, amnion, allantois, serosa