The concept of irritability. Microorganisms, plants and animals respond to a wide variety of environmental influences: mechanical influences (puncture, pressure, shock, etc.), temperature changes, intensity and direction of light rays, sound, electrical stimulation, changes in the chemical composition of the air , water or soil, etc. This leads to certain fluctuations in the body between a stable and unstable state. Living organisms are capable, as they develop, of analyzing these states and reacting to them accordingly. Similar properties of all organisms are called irritability and excitability.
Irritability is the body’s ability to respond to external or internal influences.
Irritability arose in living organisms as an adaptation that provides better metabolism and protection from the effects of environmental conditions.
Excitability- this is the ability of living organisms to perceive the effects of stimuli and respond to them with an excitation reaction.
Environmental influences affect the state of the cell and its organelles, tissues, organs and the body as a whole. The body responds to this with appropriate reactions.
The simplest manifestation of irritability is movement. It is typical even for the simplest organisms. This can be observed in an experiment on an amoeba under a microscope. If small lumps of food or sugar crystals are placed next to the amoeba, it begins to actively move towards the nutrient. With the help of pseudopods, the amoeba envelops the lump, drawing it inside the cell. A digestive vacuole is immediately formed there, in which food is digested.
As the structure of the body becomes more complex, both metabolism and manifestations of irritability become more complex. Single-celled organisms and plants do not have special organs that provide the perception and transmission of irritations coming from the environment. Multicellular animals have sensory organs and a nervous system, thanks to which they perceive irritations, and responses to them achieve great accuracy and expediency.
Irritability in unicellular organisms. Taxis.
The simplest forms of irritability are observed in microorganisms (bacteria, single-celled fungi, algae, protozoa).
In the example with the amoeba, we observed the movement of the amoeba towards the stimulus (food). This motor reaction of unicellular organisms in response to irritation from the external environment is called taxis. Taxis is caused by chemical irritation, which is why it is also called chemotaxis(Fig. 51).
Rice. 51. Chemotaxis in ciliates
Taxis can be positive and negative. Let's place a test tube with a culture of ciliates-slippers in a closed cardboard box with a single hole located opposite the middle part of the test tube, and expose it to light.
After a few hours, all the ciliates will concentrate in the illuminated part of the test tube. This is positive phototaxis.
Taxis are characteristic of multicellular animals. For example, blood leukocytes exhibit positive chemotaxis towards substances secreted by bacteria, concentrate in places where these bacteria accumulate, capture and digest them.
Irritability in multicellular plants. Tropisms. Although multicellular plants do not have sensory organs or a nervous system, they nevertheless clearly exhibit various forms of irritability. They involve changing the direction of growth of a plant or its organs (root, stem, leaves). Such manifestations of irritability in multicellular plants are called tropisms.
Stem with leaves show positive phototropism and grow towards the light, and the root - negative phototropism(Fig. 52). Plants respond to the Earth's gravitational field. Pay attention to the trees growing along the mountainside. Although the soil surface has a slope, trees grow vertically. The response of plants to gravity is called geotropism(Fig. 53). The root that emerges from a germinating seed is always directed downwards towards the ground - positive geotropism. A shoot with leaves developing from a seed is always directed upward from the ground - negative geotropism.
Tropisms are very diverse and play a large role in plant life. They are clearly expressed in the direction of growth in various climbing and climbing plants, such as grapes and hops.
Rice. 52. Phototropism
Rice. 53. Geotropism: 1 - a flower pot with straight-growing radish seedlings; 2 - a flower pot placed on its side and kept in the dark to eliminate phototropism; 3 - the seedlings in the flower pot bent in the direction opposite to the action of gravity (the stems have negative geotropism)
In addition to tropisms, plants exhibit other types of movements - nastia. They differ from tropisms in the absence of a specific orientation to the stimulus that caused them. For example, if you touch the leaves of a bashful mimosa, they quickly fold longitudinally and fall downwards. After some time, the leaves return to their previous position (Fig. 54).
Rice. 54. Nastia at the shy mimosa: 1 - in good condition; 2 - when irritated
The flowers of many plants respond to light and humidity. For example, a tulip's flowers open in the light and close in the dark. The dandelion's inflorescence closes in cloudy weather and opens in clear weather.
Irritability in multicellular animals. Reflexes. Due to the development of the nervous system, sensory organs and organs of movement in multicellular animals, the forms of irritability become more complex and depend on the close interaction of these organs.
In its simplest form, such irritation occurs in coelenterates. If you prick a freshwater hydra with a needle, it will shrink into a ball. External irritation is perceived by a sensitive cell. The excitement that arises in it is transmitted to the nerve cell. The nerve cell transmits excitation to the skin-muscle cell, which reacts to irritation by contracting. This process is called reflex (reflection).
Reflex- This is the body's response to irritation carried out by the nervous system.
The idea of a reflex was expressed by Descartes. Later it was developed in the works of I.M. Sechenov and I.P. Pavlov.
The path traversed by nervous excitation from the organ that perceives the irritation to the organ that performs the response is called reflex arc.
In organisms with a nervous system, there are two types of reflexes: unconditioned (innate) and conditioned (acquired). Conditioned reflexes are formed on the basis of unconditioned ones.
Any irritation causes a change in metabolism in cells, which leads to excitation and a response occurs.
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§ 46. Types of metabolism in organisms§ 48. Life cycle of a cell
The phenomenon of irritability is also well expressed in plant cells. Most often, plants exhibit manifestations of irritability in the form of slow motor reactions. Such slow movements directed towards or away from a stimulus are called tropisms. Phototropisms are widespread in plants - movements that occur in response to the action of light. Plants are drawn to the light, bend towards it, and this reaction is based on the irritability of their cells.
Sometimes plant cells quickly respond to stimuli. An example is the rapid response of a plant known as the shy mimosa. Whenever you touch a mimosa, when placed in the dark or in high temperature conditions, its leaves fold and seem to fade. As soon as the effect of the irritant ceases, the mimosa leaves return to their previous position. This rapid reaction of mimosa is also based on the irritability of its cells. Another example of a plant’s quick response to a stimulus. In swamps, and sometimes along the banks of streams, sundew grows - a plant that feeds on insects. Sundew is a small plant with a rosette of creeping leaves that look like spatulas. The surface of each leaf is covered with sensitive red hairs. The tip of each hair is thickened and covered with droplets of juice, shiny like dew and sticky like glue. If an insect, for example a mosquito or a small beetle, lands on such a leaf, the sticky sap of the hairs immediately impedes its movement and the insect finds itself in a trap. The leaf hairs touched by the insect quickly fold over the caught prey and pour juice abundantly over it. The juice secreted by the secretory cells of the leaf contains enzymes that break down proteins. The insect is digested and absorbed after a few hours. After this, the leaf hairs rise, and the leaf is again ready to “hunt”.
Compared to multicellular animals, the reactions of unicellular organisms and plants that occur in response to a stimulus are relatively simple: their cells directly interact with the external environment. In complex multicellular animals and humans, the nervous system in the process of evolution has become the main intermediary between the organism and the environment. Humans and animals receive information about changes in the external and internal environment through receptors - special cells that are highly sensitive to the effects of various stimuli.
A person has 5 types of external receptors, which are known to you from a physiology course (remember and name them). There are also many internal receptor cells. For example, pain receptor cells are scattered throughout the body, and in the walls of large blood vessels there are sensitive cells that respond to changes in the concentration of CO2 in the blood.
Irritability is one of the main signs of life. While the body is alive, it is irritable. With the end of life, irritability disappears. The enormous significance of the irritability of cells and organisms lies in the fact that it allows all living beings to be in constant communication with the outside world and makes it possible to adapt to it. Cell irritability is associated primarily with the large changes that occur in the proteins that make up the membranes of the cytoplasm and nucleus of each cell. When exposed to stimuli, as is now known, changes occur in the structure of protein molecules. The ability to change structure in response to stimuli is, apparently, one of the primary elementary properties of proteins, which arose during the evolution of organisms.
Movement. Closely related to irritability is the ability of cells and organisms to perform movements. The basis of movement is the contractility of the cytoplasm of cells. Contractility is one of the main properties of the cytoplasm of living cells.
As a rule, plants grow motionless in one place, and the only exceptions are some unicellular algae (for example, diatoms), capable of independent movement. We have already seen that plants respond to external stimuli such as light by moving their leaves and shoots. In addition, in plants, movement is manifested in growth.
In the cells of all plants, the cytoplasm constantly moves. These movements are called cytoplasmic currents. They can be seen using a microscope in algae, in the cells of Tradescantia leaves and in other plant cells. Cytoplasmic currents are also present in animal cells, and they are easy to observe, for example, in such protozoa as ciliates.
The ability to move in the external environment is characteristic of many species of bacteria, protozoa, and the vast majority of multicellular animals. In organisms capable of movement in the external environment, there are 4 types of cell movement: amoeboid, ciliary, flagellar and muscle.
3. Some general concepts of genetics
The nature of the gene and genotype. Having become familiar with the basic laws of genetics, we can now sum up some results and deepen our understanding of the nature of the gene and genotype of organisms. The hereditary basis (genotype) of an organism is a complex system composed of individual relatively independent elements - genes. The reality of the gene is proven by two main groups of facts: 1) relatively independent combination during splitting, 2) the ability to change - to mutate. One of the main properties of a gene is its ability to duplicate, which occurs during cell division (doubling of chromosomes). Genes have significant stability, which determines the relative constancy of the species. There is close interaction between genes, as a result of which the genotype as a whole cannot be considered as a simple mechanical sum of genes, but is a complex system that has developed during the evolution of organisms.
The material basis of genes and genotype are chromosomes, which include DNA and proteins. The biochemical (molecular) basis of the above gene properties is the ability of DNA to self-duplicate (reduplicate). The action of a gene during the development of an organism is based on its ability to determine the synthesis of proteins through RNA. The DNA molecule contains, as it were, information that determines the composition of protein molecules. It is especially remarkable that this mechanism is common at all stages of the evolution of the organic world - from viruses and bacteria to mammals and flowering plants. This indicates that the biological role of nucleic acids was determined very early in the evolution of life, perhaps at the very moment of the transition from nonliving to living.
Despite great strides in the development of genetics, especially over the past ten years, many questions have not yet been resolved by science. Thus, the question of how genes act during the development of an organism is not yet clear. The fact is that each cell has a Diploid set of chromosomes, and therefore the entire set of genes of a given species. Meanwhile, it is obvious that only a few genes function in different cells and tissues, namely those that determine the properties of a given cell, tissue, or organ. What is the mechanism that ensures the activity of only certain genes? This problem is now being intensively studied in science. There is already some evidence indicating that the leading role in the regulation of gene action belongs to proteins that are part of chromosomes along with DNA.
1. How do plants respond to stimulation?
Irritation— it is an external or internal influence that causes the plant to move. Factors that exert such influence are called irritants(light, touch, etc.). These irritations in many cases cause excitation in the cells, which manifest themselves in an increase in their activity, which can result in cell division and growth, changes in pressure inside the cells, which determine the movements of plants. For example, in an insectivorous plant round-leaved sundew, which grows in sphagnum bogs and peat bogs, the leaves have sticky hairs, at the tips of which transparent drops of liquid glisten, attracting small insects. As soon as the insect touches these hairs, it sticks to drops of thick mucus and, trying to free itself, irritates other hairs. Mechanical irritation leads to an excitation in the leaf, which causes its edges to bend inward. The leaf, carrying out contractile movements, slowly wraps its victim on all sides and digests it with the help of substances that are secreted by other hairs.
2. What is the significance of plant growth movements?
Growth movements— These are active plant movements associated with growth processes. In most plants, these movements cover only individual organs - root, shoot, flower. Growth movements are the result of rapid growth of cells on one side of the organ under the influence of environmental factors. The reason for growth movements in plants is changes in illumination and temperature during the day. Growth movements are divided into tropisms And Nastia. Tropisms— these are growth movements in the direction determined by the unilateral influence of a certain environmental factor. These movements can be directed towards the stimulus (movement of sunflower baskets towards the sun, etc.), or away from it (growth of ivy roots in the direction opposite to the light). As a result of such movements, the plant occupies the most advantageous position in space and avoids everything dangerous to its life. Nastia— these are growth movements in a direction that is determined by internal factors, and external influences only predetermine their occurrence. They are caused by uneven growth of the lower and upper sides of the leaf and petal. They can be observed throughout the day, when light periodically gives way to darkness. Some plants have flowers that open in the morning and close at night. Dandelion baskets and water lily flowers close at night and open in the morning. And in matthiola and fragrant tobacco, the flowers close during the day and open at night.
3. What is the significance of contractile movements in plants?Material from the site
The activity of plants that lead an attached lifestyle can be associated not only with growth, but also with contractile movements. Contractive movements— These are active movements of plants, which are caused by changes in pressure inside certain groups of cells, as a result of which their sizes change. An example of such movements is the lowering of the leaves of mimosa pudica when touched, the opening of tulip flowers when transferred from cold to warm, etc. Legumes (beans, clover, etc.) have special leaf pads in their leaves that are formed at the base petiole or leaf, which contains large cells. The rapid change in pressure in the upper and lower cells due to the movement of water leads to the fact that the leaf pad acts as a hinge, with the help of which the leaves either lower or rise. So, growth and contractile movements are the main active reactions of plants in response to irritation from environmental factors.
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On this page there is material on the following topics:
- vidpovіd roslin on the subtitles abstract
- Growth movements (tropisms and nasties) and their significance in plant life
- plant response to external stimuli
- plant response to environmental factors
- message on the topic: plant response to irritation
Irritability is the general biological ability of cells and organisms to react (respond) to the influence of environmental factors. The most important element in the process of irritability are receptors. Receptor cells are called biological sensors or transducers, since they convert the energy of pressure, light, chemical and other factors into electrical impulses. Plants have receptors that are not as differentiated as animals. They are ectodesmas, starch statoliths, sensitive hairs, etc.
The main forms of manifestation of irritability in organisms are various types of motor reactions that are carried out by the whole organism or its individual parts. The most common motor reactions of living organisms to changes in environmental conditions are taxis, and in plants (except for taxis) - tropisms, nasties, nutations and autonomous movements.
Taxis are the movement of an organism, manifested in its spatial movement relative to the stimulus (amoeba, ciliate). If the movement of the organism is carried out in the direction of the acting factor, then such taxis is called positive; and negative when the movement occurs in the opposite direction.
Taxis are classified depending on the type of stimulus. Reaction to action: light - phototaxis, chemical compounds - chemotaxis, temperature - thermotaxis. An example of positive phototaxis is the oriented movement of flagellated unicellular algae (Chlamydomonas) to the zone of optimal lighting in an aquarium or pond, the appropriate orientation of chloroplasts in the mesophyll cells of a leaf; chemotaxis - accumulation of bacterial cells near a dead ciliate cell, movement of leukocytes towards the bacterium, etc.
Tropisms are a motor response of plant organs and parts to the unilateral influence of an environmental factor (light, gravity, water, chemicals, etc.).
Depending on the plant organism, tropisms can be positive when, due to uneven growth, an organ or part of the plant bends towards the active factor, and negative when growth processes cause deviations of the organ in the opposite direction. In plants, geotropism is best expressed - the reaction of its individual organs to the unilateral influence of the force of gravity.
There are three types of geotropism: positive - when the organ grows vertically downwards, negative - when the direction of movement is the opposite, and transverse, or diageotropism, when the organ tries to take a horizontal position. The main tap roots have, as a rule, positive geotropism; branches of the first order of woody plants, petioles of many leaves - negative; many rhizomes, lateral roots - transverse.
Phototropisms are growth movements of plants in response to unilateral exposure to light. With one-sided exposure to light (in a clearing, near buildings, in a room, etc.), the phototropism of individual shoots or even the entire above-ground part is especially clearly manifested. Plants seem to be drawn to the light (plants on the windowsill, sunflower inflorescences, leaves on the shoots).
Other physical and chemical factors can also have a one-sided effect on growing organs. Accordingly, chemotropisms, hydrotropisms, thermotropisms, and magnetotropisms are also distinguished (i.e., the classification of tropisms depends on the source of irritation).
Nastya. Nastic movements include movements that are a response of organs or parts of plants to the action of stimuli that do not have a specific direction, but affect diffusely and evenly from different directions. That is why it is impossible to establish any one-sided factor of the motor reaction.
Epinasty - when an organ (usually a leaf) bends downward. This may be due to accelerated growth or turgor stretching of the upper side of the petiole (dropping of leaves of mimosa, vetch, white acacia).
Hyponasty - bending of an organ due to accelerated growth or stretching of cells on the lower side of the petiole and central vein (raising of leaf blades at night in quinoa, tobacco).
Nyctinasties are motor reactions caused by the onset of darkness, the so-called sleep in plants (closing flowers, lowering the inflorescences of carrots at night).
Photonasty - opening of flower petals when lighting increases (chicory, dandelion, potato inflorescences).
Thermonasty - opening of petals when the temperature rises (tulip, coltsfoot, garden poppy).
Seismonasty is the movement of plant organs that are a response to a shock or shock (mimosa, sorrel, purslane).
Nutations. Nutations are understood as the ability of plants to perform circular or pendulum movements due to periodically repeating changes in the values of turgor pressure and the intensity of growth of opposite sides of a certain organ. This is best expressed at the tops and tendrils of climbing plants. In climbing plants, during growth, the apex makes uniform nutational movements and, upon contact with a support, begins to twine around it (hops, pumpkin, peas, beans).
Irritability is a universal property of all living things to respond to environmental influences.
From the textbook
§42.ANIMAL IRRITABILITY
Basic concepts: ANIMAL IRRITABILITY. SENSE ORGANS
Remember! What is irritability?
Think
The presence of irritability in plants is proven through research that demonstrates the growth movements of the root and shoot in the bean seedling. This is due to the fact that the shoot reacts to light by growing, and the root perceives the force of gravity and grows downward. How can you be sure that animals are irritable?
I l. 167. Plant growth movements
What are the characteristics of animal irritability?
Irritability in animals manifests itself in the ability to respond to environmental influences with active activity. For example, at morning sunrise, birds wake up and begin to sing, or touching a grape snail makes it hide in the plowing. In these examples, light or touch will be stimuli, the process of action of this force will be irritation, and the response of birds or snails to the action of factors will be a biological reaction. Irritants for animals can be light, mechanical stress, temperature, salt composition of water, food, humidity, water, sounds, chemicals and many other factors.
I l. 168. The finch is one of the most common songbirds
A sign of irritability at the cellular level is a positive electrical charge on the surface of the cell and a negative charge inside the cell. This charge difference can change under the influence of various factors, which is the beginning of intracellular processes. Changes in cellular metabolism determine the cell's response to the influence of the factor. Irritability is also characteristic of the cytoplasm of cells, which is capable of perceiving environmental influences and responding to them by the occurrence or cessation of movement. In multicellular animals, tissues that are characterized by excitability participate in the production of irritability. These are nervous, muscular and certain types of epithelial. The conduction of excitation to ensure movement, the release of secretions is associated with such organs as nerves, spinal cord and brain, muscles, and secretion glands. In shaping the animal’s response to environmental influences, the nervous and endocrine systems are of decisive importance.
Consequently, ANIMAL IRRITABILITY is the ability to move from a resting state to an active state in response to the action of environmental factors, realized at different levels of their organization.
What are the forms of irritability in animals?
Biological responses of animals to environmental influences manifest themselves in the form of taxis and reflexes. Unlike the growth or hygroscopic movements of plants and fungi, in animals these reactions are motor.
Taxis is a motor reaction in response to the directed influence of a factor, carried out by cells or organisms. For example, the ejection of a thread from a hydra stinging cell upon touching a sensitive outgrowth is mechanotaxis, and the movement of amebocytes towards nutrients or away from harmful substances is positive or negative chemotaxis. Taxis provide spatial orientation of animal movements to the action of favorable or unfavorable stimuli.
Reflexes are a motor response of the body to a specific trigger stimulus, carried out with the obligatory participation of the nervous system. For the first time, reflexes as forms of irritability appear in coelenterates due to the emergence of a diffuse nervous system in them. Reflexes can be innate unconditioned (compression of the hydra’s body into a lump after mechanical action) or acquired conditioned (food reflexes of fish that are formed when feeding at the same time).
Il. 169. Taxis of amebocytes
I l. 170. Unconditioned protective reflex of the hydra
Taxis and reflexes are constant components in animal behavior. If reflexes determine the occurrence and course of an animal’s biological reaction, then taxis provide its direction. For example, the appearance of a seagull with food triggers the reaction of the chicks (unconditioned food reflex), and the red spot on its beak directs the reaction of these chicks to its beak (positive phototaxis).
So, the biological reactions of animals to the influence of factors is the relationship between taxis and reflexes.
Il. 171. Forms of irritability in tern chicks
What is the sign of the senses for the animal body?
SENSE ORGANS are anatomical formations of the animal body that perceive information from the external or internal environment. This information comes in the form of effects of sound, light, chemicals and is important for turning on and off various biological reactions.
The main sense organs in animals are vision, hearing, smell, taste and touch. For mobile animals, the organs of balance are of great importance. Certain groups of animals may have specific sensory organs associated with their lifestyle. Thus, fish have a lateral line, pit snakes have organs for perceiving heat rays, and dolphins and sperm whales have organs for perceiving reflected sounds.
What is the importance of sense organs for animals?
The most primitive organs of vision, which are light-sensitive eyes (jellyfish, free-living flatworms), allow us to distinguish light from darkness. Simple eyes (spiders) allow one to distinguish the strength and direction of light and to detect the movements of objects. Compound eyes of insects, cephalopods and vertebrates. Such eyes already distinguish the shape, volume and color of objects. Thanks to their visual organs, animals navigate their environment, successfully obtain food during daylight hours, and protect themselves from enemies.
Sound - vibrations of the air or water environment or solid substrate - plays a dual role in the life of animals. On the one hand, it is a signal of danger, and on the other, it is a way of communication. Sound-sensing organs are already present in jellyfish. They perceive low-frequency vibrations and will allow you to “anticipate” a storm. The perception and reproduction of sounds is well developed in arthropods, in particular insects. their hearing organs can be located on the legs, abdomen, and antennae. The organ of hearing is most important for terrestrial vertebrates, so their auditory system is difficult: amphibians have an eardrum, reptiles have an external auditory canal, birds and some mammals have an external ear, and mammals already have all three auditory ossicles.
Sensitivity to chemical stimuli is one of the oldest types of senses. In animals it is provided by the organs of smell and taste, which play an important role in searching for food, individuals of the opposite sex, recognizing individuals of their own species, avoiding predators and harmful influences. Among terrestrial invertebrates, the chemical sense organs reached their greatest development in arthropods, especially in insects, and among vertebrates - in mammals.
Mechanical influences of the environment (touch, pressure, vibration) in invertebrates are perceived by sensitive structures of the integument in the form of cilia, hairs, antennae, and in vertebrates - by skin receptors.
Consequently, environmental information is very diverse, and therefore the sense organs of animals are also diverse.
ACTIVITY
Laboratory research
ANIMAL SENSE ORGANS
Goal: to consolidate knowledge about the sense organs of animals; to develop the ability to characterize the sensory organs of various groups of animals using the example of specific representatives.
Equipment: drawings, insect collections, wet preparations of crayfish and fish.
Progress
1. Examine the body of the crayfish and determine the name, features and location of the organs of vision, touch, smell and taste.
2. Examine the body of the cockchafer and determine the name, features and location of the organs of vision, touch, smell and taste.
3. Examine the body of the river perch and determine the name, features and location of the organs of vision, smell, taste and lateral line.
4. Fill in the table.
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Name of sense organs |
Crayfish |
Khrushchev May |
River perch |
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Organs of vision |
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Olfactory organs |
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Organs of taste |
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Organs of touch |
5. State your conclusion.
Learning to know
Mini-project “HOW DO ANIMALS SEE?”
For centuries, people had no idea how animals see the world. But today science gives us the opportunity to look into the wonderful world of diversity of animal visual organs. Use the guiding rule (see appendix) to create a mini-project and, using the example of the six proposed animals (cat, horse, dragonfly, pigeon, monkey, snake) or animals that you choose yourself, describe the capabilities of the animals’ visual organs.
RESULT
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Questions for self-control |
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1. What is irritability? 2. What is the meaning of irritability? 3. Name the main forms of irritability in animals. 4. Give an example of the taxis and reflexes of animals. 5. What are sense organs? 6. Name the main sense organs of animals. |
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7. What are the features of irritability in animals? 8. What are the forms of irritability in animals? 9. What is the importance of sense organs for the animal body? |
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10-12 |
10. Describe the sensory organs of different groups of animals, using specific representatives. |
