1. Remember what is called tissue in biology.
A tissue is a collection of cells, as well as intercellular substance, that have a similar structure, origin and function.
2. What are the four types of fabrics?
There are epithelial, connective, muscle, and nervous tissues.
3. What is intercellular substance?
Intercellular substance- a substance that fills the spaces between cells, which is a product of the vital activity of adjacent cells. In different types of tissues it can be expressed differently: from poorly developed in epithelial tissues to well developed in connective tissues. Depending on the functions performed, the intercellular substance can be different: liquid in blood, dense in bones, elastic in cartilage. The composition of the intercellular substance includes various substances: lymph, blood plasma, reticulin, elastin and collagen protein fibers, as well as amorphous substances, or matrix, which consists of a set of complex organic matter.
4. What features are characteristic of epithelial tissue? Where is it found?
Epithelium lines the surface of the skin (keratinizing), oral cavity, esophagus (multilayer non-keratinizing), alveoli, nephron capsules (single-layer); glandular epithelium forms salivary glands, glands of the skin, stomach, intestines, internal secretion; ciliated epithelium lines Airways and fallopian tubes.
Epithelial tissue is formed by both ecto- and endoderm, and has a high ability to recover. The epithelium forms one or more layers of cells lying on a thin basement membrane, devoid of blood vessels. The cells adhere tightly to each other, forming a continuous layer; there is almost no intercellular substance. The epithelium is nourished by the underlying connective tissue.
5. Which tissue recovers most quickly after damage?
Epithelial.
6. Make a diagram reflecting the diversity of connective tissues.
7. Why liquid blood classified as fabrics?
Blood cells have the same structure, common origin and well-developed intercellular substance, which in blood is liquid, depending on the function performed by the tissue, which means blood is a tissue by definition (tissue is a collection of cells, as well as intercellular substance, having a similar structure, origin and functions ).
1. Make a table " Comparative characteristics different types muscle tissue", having previously discussed the comparison criteria.
Sample table.
9. What is a neuron? How is it built?
A neuron is the basic functional unit of nervous tissue. Neurons vary in shape and size, but overall plan the structure of neurons is the same. A neuron consists of a body (the bodies form the gray matter of the brain and spinal cord) and processes. Short processes of neurons - dendrites, are multiple and ensure the transfer of excitation from one neuron to another, establishing communication between different organs. The long process of a neuron is a single axon, which can reach a length of up to 1 m; in organs it ends with branched nerve endings. Axons are pathways nervous system, form the white matter of the spinal cord and brain, due to the fact that the processes are covered with a light myelin sheath.
10. What role does neuroglia play in the functioning of the nervous system; synapse?
Neuroglia provide support, nutrition, and protection to neurons; it is formed by cells - neurocytes, and is located between neurons.
Synapses are places where neurons contact each other or a muscle fiber or a secreting gland. Thanks to synapses, excitation is transmitted through irritation of receptors with electrical impulses or release chemical substances into the synaptic cleft.
11. Formulate definitions of the concepts “organ”, “organ system”.
An organ is a part of the body that has a certain shape and structure, occupies a certain place in the body and performs a certain function.
An organ system is a group of anatomically interconnected organs that have a common origin and a common structural plan and perform a common function.
12. List the organs in the human body that you know.
Brain and spinal cord, pituitary gland, pineal gland, hypothalamus, thyroid, parathyroid glands, adrenal glands, kidneys, pancreas, spleen, liver, heart, lungs, small and large intestines, stomach, esophagus, uterus, ovaries, testicles, prostate, hearing organ, eye, tongue, diaphragm, skin, salivary glands, gallbladder, bladder, thymus, red and yellow bone marrow.
13. Remember which organs are called rudimentary, atavistic. Give examples.
Rudiments are organs or parts of organs that were well developed in ancestral forms, but do not function in distant descendants, are in the process of disappearing, or have acquired new characteristics during evolution. For example: semilunar fold - the remnant of the nictitating membrane (third eyelid) in the corner of the eye, palatal ridges, wisdom teeth, nasal muscles and ears, hairline on the body.
Atavism is the appearance in individual individuals of a species of characteristics that existed in distant ancestors, but were lost during the process of evolution. For humans, this is hairiness of the whole body, the appearance of additional breast nipples, tailedness, fangs, highly developed swimming membranes between the fingers, and movable ears.
Textile- a collection of cells and intercellular substance that have general structure, function and origin.
Epithelial tissue
Functions
- Border ( outer layer skin, inner layer respiratory tract, lungs, stomach, intestines).
- Secretion of substances (glands).
Features of the structure:
- The cells are tightly adjacent to each other, there is little intercellular substance.
- Cells divide very quickly, due to this, damage to the epithelium is quickly healed.
Connective tissue
Functions
- Nutritional (blood, adipose tissue)
- Supporting (bone, cartilage, connective tissue membrane of all organs).
Features of the structure: there is a lot of intercellular substance.
Muscle
Functions: excitability and contractility.
| Three types of muscle tissue | striated skeletal | striated heart | smooth |
| Included in | skeletal muscles (for example, limb muscles) | hearts | internal organs(stomach, blood vessels, etc.) |
| cells | multi-core | single-core | |
| control | obeys consciousness (innervated by the somatic nervous system) | does not obey consciousness (innervated by the autonomic nervous system) | |
| is declining | fast | slowly | |
Nervous tissue
Functions: excitability and conductivity.
The main cells of nervous tissue are neurons- consist of a body and processes. There are two types of shoots:
- dendrites - short, branched, accept excitation;
- axon - long, unbranched, transmits excitation.
In addition to neurons, nervous tissue also contains satellite cells(neuroglia), there are 10 times more of them than neurons, they perform nutritional, supporting and protective function.
Axons may be coated with a white, fat-like substance called myelin, which speeds up the conduction of nerve impulses. The accumulation of such axons forms white matter nervous system. Companion cells, neuron bodies and dendrites form Gray matter.
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PART 2 ASSIGNMENTS:
Tests and assignments
Establish a correspondence between the characteristics of human tissue and its type: 1) epithelial, 2) connective. Write numbers 1 and 2 in the correct order.
A) transports substances in the body
B) forms the epidermis of the skin
D) produces antibodies
E) contains a lot of intercellular substance
Answer
Choose one, the most correct option. What functions do satellite cells perform in nervous tissue?
1) the occurrence of excitation and its conduction along nerve fibers
2) nutritional, supportive and protective
3) transmission of nerve impulses from neuron to neuron
4) constant renewal of nervous tissue
Answer
All but two of the characteristics listed below can be used to describe the fabric shown in the picture. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) ability to contractility
2) the presence of a large number of cores
3) ability to conduct aqueous solutions
4) ability to conduct impulses
5) the presence of a well-developed intercellular substance
Answer
1. Choose three correct answers out of six and write down the numbers under which they are indicated. What functions does connective tissue perform in the human body?
1) performs a reflex function
2) participates in the transport of oxygen from the lungs to cells
3) ensures consistency of composition internal environment
4) produces digestive enzymes
5) forms subcutaneous fatty tissue
6) traps and removes dust particles in the nasal cavity
Answer
2. Select three features of connective tissue.
1) Cells adhere tightly to each other
2) There is little intercellular substance
3) Well developed intercellular substance
4) Fills gaps between organs
5) Cells are diverse in structure and function
Answer
3. Select two features that characterize the characteristics of human connective tissue. Write down the numbers under which they are indicated.
1) the intercellular substance is well developed
2) cells are always mononuclear
3) cells contain the protein myosin
4) cells contain many mitochondria
5) the fabric may be liquid
Answer
4. Choose three correct answers out of six and write down the numbers under which they are indicated. Connective tissue of the human body
1) represented by blood, lymph, cartilage
2) lines the mucous membranes of the stomach and oral cavity
3) can be liquid or solid
4) has excitability and conductivity
5) has a weakly expressed intercellular substance
6) performs a transport function
Answer
Establish a correspondence between the characteristics of the tissue and the type of tissue that has this characteristic: 1) epithelial, 2) connective, 3) muscle. Write the numbers 1, 2 and 3 in the correct order.
A) consists of mononucleated and multinucleated cells
B) can be liquid, solid, elastic
B) lines the mucous membranes of organs
D) forms digestive glands
D) the intercellular substance is highly developed
E) has excitability
Answer
Establish a correspondence between the characteristics of human tissues and their types: 1) muscle, 2) connective. Write numbers 1 and 2 in the order corresponding to the letters.
A) capable of storing fat
B) some cells contain hemoglobin
B) its cells are long and cross-striated
D) has contractility and excitability
D) the intercellular substance is well developed
E) cells are mononuclear or multinucleate
Answer
Choose three options. Tissues have properties of excitability and contractility
1) cardiac muscle
2) glandular epithelial
3) smooth muscle
4) nervous
5) loose connective
6) striated muscle
Answer
Choose one, the most correct option. Changes in the diameter of blood vessels occur due to tissue
1) epithelial
2) connecting
3) smooth muscle
Answer
1. Choose three options. Striated muscle tissue, as opposed to smooth
Answer
2. Choose three correct answers out of six and write down the numbers under which they are indicated. What are the features of striated muscle tissue?
1) forms muscles located in the walls of internal organs
2) consists of spindle cells with one nucleus
3) forms skeletal muscles
4) consists of long multinucleated cells
5) has fibers with transverse striations
6) participates in changing the lumens of blood vessels
Answer
3. Choose three correct answers out of six and write down the numbers under which they are indicated. Human striated muscle tissue
1) forms the muscles of blood vessels
2) is part of the tongue, pharynx and the initial part of the esophagus
3) performs involuntary contractions
4) has motor centers in the cerebral cortex
5) regulated by the somatic part of the nervous system
6) consists of single spindle cells
Answer
Choose one, the most correct option. Changes in the lumen of arteries occur in humans due to tissue
1) epithelial
2) connecting
3) smooth muscle
4) striated muscle
Answer
Choose one, the most correct option. Gray matter in the brain and spinal cord person educated
1) bodies of sensory neurons
2) long processes of motor neurons
3) long processes of sensory neurons
4) bodies of motor and interneurons
Answer
Establish a correspondence between the characteristics and types of human tissue: 1) epithelial, 2) connective, 3) nervous. Write the numbers 1, 2 and 3 in the correct order.
A) has conductivity
B) performs the function of support and nutrition
B) forms the outer covering of the skin
D) produces antibodies
D) consists of closely adjacent cells
E) forms the gray matter of the spinal cord
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. The human heart muscle is characterized
1) the presence of transverse striations
2) abundance of intercellular substance
3) spontaneous rhythmic contractions
4) the presence of spindle cells
5) numerous connections between cells
6) absence of nuclei in cells
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Smooth muscle tissue, as opposed to striated muscle tissue
1) consists of multinucleated cells
2) consists of elongated cells with an oval nucleus
3) has greater speed and energy of contraction
4) forms the basis of skeletal muscles
5) located in the walls of internal organs
6) contracts slowly, rhythmically, involuntarily
Answer
Establish a correspondence between the characteristics of the tissue and its type: 1) epithelial, 2) connective. Write numbers 1 and 2 in the correct order.
A) intercellular substance is practically absent
B) performs nutritional and support functions
B) lines the inside of the intestinal cavity and other organs
D) forms subcutaneous fat tissue
D) is a component (part) of the internal environment of the body
Answer
Match the characteristics and types of human tissue shown in the figure. Write numbers 1-4 in the correct order.
A) consists of multinucleated cells
B) has excitability and conductivity
B) cells adhere tightly to each other
D) contains elastic fibers
D) the cell has a body and processes
E) capable of contractility
Answer
B) contains a lot of intercellular substance
B) forms sweat glands
D) provides gas transport
D) forms the surface layer of the skin
E) performs supporting and mechanical functions
Answer
Establish a correspondence between the characteristics of human tissue and its type: 1) epithelial, 2) connective.
A) consists of cells tightly adjacent to each other
B) consists of loosely arranged cells
B) contains liquid or solid intercellular substance
D) forms nails and hair
D) provides communication between organs
Answer
Establish a correspondence between the characteristics of the tissue and its type: 1) epithelial, 2) connective.
A) transport of substances in the body
B) close adherence of cells to each other
B) abundance of intercellular substance
D) release of enzymes and hormones
D) participation in the formation of skin
Answer
Establish a correspondence between the characteristics of human tissue and its type: 1) epithelial, 2) connective, 3) nervous.
A) regulation of body movements
D) protection from chemical influences
D) sweating
Answer
Establish a correspondence between the functions of tissues and their type: 1) epithelial, 2) connective, 3) nervous.
A) regulation of vital processes
B) storage of nutrients
B) movement of substances in the body
D) protection from mechanical damage
D) ensuring metabolism between the body and the environment
Answer
Establish a correspondence between the feature and the type of human muscle tissue for which it is characteristic: 1) smooth, 2) cardiac
A) formed by spindle cells
B) cells have transverse striations
B) cells are mononuclear
D) muscles have high speed reductions
Answer
Establish a correspondence between the properties and human tissues: 1) Muscular, 2) Nervous. Write numbers 1 and 2 in the correct order.
A) conducts an electrical impulse
B) cells are capable of contraction
B) can be smooth or striated
D) cells can have several nuclei
D) cells have exactly one nucleus
E) most cells have many processes
Answer
Establish a correspondence between the characteristics of human tissue and its type: 1) Epithelial, 2) Connective. Write numbers 1 and 2 in the correct order.
A) cells adhere tightly to each other
B) cells can be flat, cubic, cylindrical
C) the tissue is ciliated, glandular, keratinized
D) the tissue is of mesodermal origin
D) tissue can be liquid or solid
E) the intercellular substance is well developed
Answer
Establish a correspondence between the types of tissues and their characteristics: 1) muscle, 2) nervous. Write numbers 1 and 2 in the order corresponding to the letters.
A) has excitability and conductivity
B) represented by myocytes
B) capable of contracting
D) represented by neurons
D) ensures communication between organs and their coordinated work
E) ensures body movement and the functioning of internal organs
Answer
Establish a correspondence between the function of tissue in the human body and its type: 1) epithelial, 2) connective. Write numbers 1 and 2 in the order corresponding to the letters.
A) movement of substances in the body
B) production of hormones
B) production of phagocytes
D) metabolism between the body and the external environment
D) storage of nutrients
Answer
Establish a correspondence between the structure and functions of neuron processes and their name: 1) dendrite, 2) axon. Write numbers 1 and 2 in the order corresponding to the letters.
A) ensures signal transmission from the neuron body
B) ensures signal transmission to the neuron body
C) short and highly branched
D) long and does not branch
D) externally covered with a myelin sheath
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Human epithelial tissue
1) line the inside of hollow organs
2) capable of contracting
3) capable of being excited
4) contain little intercellular substance
5) cells have a myelin sheath
6) form glands
Answer
1. Establish a correspondence between the characteristics of muscle tissue and its type: 1) striated, 2) smooth. Write numbers 1 and 2 in the order corresponding to the letters.
A) forms skeletal muscles
B) forms middle layer walls of veins and arteries
B) provides voluntary movements
D) provides intestinal peristalsis
D) consists of spindle-shaped cells
E) consists of multinucleated cells (fibers)
Answer
2. Establish a correspondence between the characteristics and types of muscle tissue: 1) smooth, 2) striated. Write numbers 1 and 2 in the order corresponding to the letters.
A) capable of rapid powerful contraction
B) consists of short spindle cells
B) the cell contains a large number of nuclei
D) myofibrils in the cell are arranged disorderly
D) is part of the walls of hollow internal organs
E) controlled by the somatic nervous system
Answer
3. Establish a correspondence between the characteristics of human tissues and their types: 1) smooth, 2) striated. Write numbers 1 and 2 in the order corresponding to the letters.
A) represented by spindle-shaped cells
B) forms the muscles of the musculoskeletal system
B) consists of multi-core elongated fibers
D) the reduction of protein fibers is slow
D) forms the middle layer of the wall of blood vessels
Answer
The following features, except two, are used to describe the structure and functions of the depicted cells. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) are eukaryotic
2) contain cell walls
3) form epithelial tissue
4) somatic cells haploid
5) capable of mitosis
Answer
Establish a correspondence between the structural and functional features of striated muscles and their type: 1) skeletal, 2) cardiac
A) attaches to bones
B) consists of long fibers that are not connected to each other
B) perceives impulses along the somatic reflex arc
D) fibers close tightly in certain areas
D) works autonomously
E) capable of contracting in all directions
Answer
Establish a correspondence between the characteristics and types of tissue: 1) striated muscle, 2) epithelial. Write numbers 1 and 2 in the order corresponding to the letters.
A) forms skeletal muscles
B) consists of cells tightly adjacent to each other
B) has the properties of excitability and contractility
D) lines the nasal cavity
D) performs a protective function
E) provides body movement
Answer
Look at the picture, identify (A) the type of tissue, (B) the type of tissue, and (C) the location of this tissue in the human body. For each letter, select the corresponding term from the list provided.
1) connecting
2) epithelial
3) striated muscle
4) smooth muscle
5) ciliated epithelium
6) stratified epithelium
7) mucous membrane of the nasal cavity
8) the inner surface of the stomach
Answer
Analyze the table. For each lettered cell, select the appropriate term from the list provided.
1) protective
2) lymphatic vessels
3) alveolar vesicles
4) smooth muscle
5) intestinal peristalsis
6) arteries, veins, capillaries
7) striated muscle
8) connecting
Answer
Establish a correspondence between the characteristics and types of tissue: 1) epithelial, 2) nervous. Write numbers 1 and 2 in the order corresponding to the letters.
A) most cells have numerous processes
B) cells unite and form layers
B) cells are capable of conducting electrical impulses
D) cells may have numerous villi
D) cells have a high ability to regenerate
E) mature cells incapable of dividing
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. What are the features bone tissue?
1) has a dense intercellular substance
2) contains glial cells
3) performs a transport function
4) formed from endoderm
5) performs a supporting function
6) consists of plates
Answer
Establish a correspondence between the characteristics and types of connective tissue: 1) bone, 2) blood. Write numbers 1 and 2 in the order corresponding to the letters.
A) intercellular substance of liquid consistency
B) performs a transport function
B) intercellular substance of dense consistency
D) performs a support function
D) provides respiratory function
E) serves as a calcium depot in the body
Answer
Match the characteristics and types of muscle tissue presented in the pictures. Write numbers 1-3 in the order corresponding to the letters.
A) formed by multinucleated cells forming long fibers
B) capable of generating and conducting an electrical impulse
B) consists of short spindle cells
D) consists of cells with lateral processes that form contacts with each other
D) controlled by the somatic nervous system
E) is located in the walls of the stomach and intestines
Answer
© D.V. Pozdnyakov, 2009-2019
The bodies of multicellular animals are made up of different types cells that perform different functions in the body. Each cell type contains not just one cell, but many similar ones. Thus, we usually talk about types of fabrics (in in this case animals) rather than cell types.
Tissue is made up not only of cells, but also of the substance between these cells. This substance is secreted by tissue cells and is called intercellular. Tissues differ from each other including the amount of intercellular substance. In some animal tissues there is a lot of it, in others the cells are tightly adjacent to each other and there is almost no intercellular substance.
Thus, textile is a collection of cells that have a similar structure and function, as well as the intercellular substance secreted by these cells.
There are four main types of animal tissue: integumentary, connective, muscle and nervous. Each type of fabric has its own subtypes. Therefore, they speak, for example, not about connective tissue, but about connective tissues.
Integumentary tissues
Integumentary tissues are called differently epithelial.
Integumentary tissues line not only the surfaces of the body, but also the cavities of internal organs. So the stomach, intestines, oral cavity, bladder, etc. are lined with integumentary tissues from the inside.
There is almost no intercellular substance in epithelial tissues. Their cells adhere tightly to each other and form from one to several layers.
The main functions of the epithelium are protection, secretion production, gas exchange, absorption, and excretion.
is expressed in the protection of the deeper tissues of the animal from damage, temperature changes, and harmful microorganisms. This function is performed by the skin.
epithelium is characteristic of the intestine. Here nutrients with the help of intestinal villi they are absorbed into the blood.
of the animal's integumentary tissue is observed in the stomach, where its cells secrete mucus. There are also various glands in the skin.
carried out by the epithelium of the lungs; in some animals the skin also takes part in gas exchange.
performs the epithelium of the excretory organs.
Connective tissues
Unlike integumentary tissues, connective tissue contains a lot of intercellular substance, which contains relatively few cells.
Connective tissues form bones, cartilage, tendons, ligaments, fatty tissue, and blood. They perform supporting, protective, connecting and other functions.
Blood is classified as connective tissue, as it connects various organs and organ systems. This is how blood carries oxygen from the lungs to all cells of the body, and carbon dioxide back. From digestive system blood delivers nutrients to cells. Harmful substances transported to the excretory system.
Muscle tissue
Main function muscle tissue is responsible for the movement of the animal. This occurs due to the alternate contraction and relaxation of the cells that make up muscle tissue. These processes are controlled by nervous tissue.
Muscle cells have an elongated shape.
There are two main types of muscle tissue: striated And smooth. The first forms the skeletal muscles of the animal. Smooth muscles are part of the internal organs. Smooth muscle cells are elongated, but shorter than those of striated muscle tissue, in which the cells are long with many nuclei.
Nervous tissue
Nervous tissue consists of special cells - neurons. These cells have a body and processes, thus the cell has a stellate shape. There are two types of shoots: short and long. The processes transmit irritations from various organs bodies in the spinal cord and brain (which consist of nervous tissue). Here the information is processed, after which excitation is transmitted from the nervous tissue to the organs, which is the body’s reaction to irritation.
The function of nervous tissue is to coordinate the work of various organs of a complex organism, control it, and respond to influences environment and etc.
Groups of cells have different purposes: some serve as support for the body, others provide nutrition, and others transport substances in the body. They have their own names according to the “work” they do.
Fabrics
A tissue is a group of cells that have a common origin. similar structure and performing a specific function in a living organism.
In some tissues, cells are located very close to each other, in others there are gaps between them - intercellular spaces (intercellular spaces).
Plant integumentary tissues
Integumentary tissues are located on the surface of all plant organs. They protect plants from adverse external influences: drying out, mechanical damage, penetration of pathogenic microorganisms into internal tissues.
Let us consider the structure of integumentary tissue using the example of leaf skin. The skin cells are alive. Most of them are large, tightly adjacent to each other, and transparent. Transparency allows sunlight to penetrate into the leaf. Other skin cells are smaller and green, as they contain chloroplasts. These cells are arranged in pairs and are called guard cells. If they move away from each other, a gap appears between them; if they move closer (closed), the gap disappears. The gap that appears between the guard cells is called stomatal, and the entire formation is guard cells with a stomatal gap - stomata.
In plants that live in dry places, the skin is covered with wax and other substances that enhance the plant’s protection from water evaporation. The skin cells of many plants form hairs. They can for a long time remain alive or quickly die and fill with air, forming a woolly or felt cover on the plant. This cover reflects part sun rays and reduces leaf heating.
Young shoots of trees and shrubs are covered with skin. Older ones have no skin. its cells die and slough off. But even before this happens, a multi-layered covering tissue, a cork, forms under the skin. The cork cells are dead, filled with air, and tightly adjacent to each other. With age, the thickness of the cork layer increases.
There are lentils in the cork. They are loosely interconnected cells. Gases pass freely through the intercellular spaces of lentils, so they, like the stomata in the lentils, ensure gas exchange of the integumentary tissues.
Cork on tree trunks and branches serves as a kind of case that more reliably protects the internal tissues of plants from adverse influences external environment than a single-layer skin. In most trees, the cork is replaced with age by a crust (bark), consisting of many layers of dead cells. A thick crust even more reliably protects tree trunks from mechanical damage (animal gnawing, forest fires, sudden temperature changes).
Animal integumentary tissues
Multicellular animals, like plants, have integumentary coverings epithelial tissue(epithelium). They cover the body of animals from the outside and line all hollow organs from the inside (vessels, respiratory tract, stomach, intestines). The outer epithelial cells are arranged in one or more layers and fit tightly together. They have a flat, elongated or cylindrical shape. The intercellular substance is poorly developed or absent.
The integumentary tissues of animals perform the same function as those of plants: they protect the body from mechanical damage, contribute to the survival of unfavorable conditions, and participate in gas exchange.
In addition, there is glandular epithelium, the cells of which are part of the glands. They perform secretory function secrete special substances (secret): saliva, digestive juices, sweat, milk. The integument of complex animals, such as animals, has multilayered epithelium. It forms upper layer skin. As a result of external influences, epithelial cells constantly die and are replaced by new ones.
Sweat and sebaceous glands develop from the outer epithelial cells.
The most important part of the leaf is the leaf blade. The outside of the leaf blade is covered with skin (epidermis). There are no chloroplasts in the skin cells, so it easily transmits light to the main tissues of the leaf. The skin cells adhere tightly to each other and reliably protect the internal tissues of the leaf.
The top of the skin may be covered with a layer of wax or a waxy substance, which also has a protective function. They prevent the penetration of pathogenic microorganisms into the leaves, protect the leaf from overheating and excessive evaporation of water. The same role is played by hairs, which are outgrowths of skin cells and sometimes densely cover the leaf. For leaves located horizontally, the skin of the upper and lower sides is slightly different in structure. Among the cells of the integumentary tissue on the underside of the leaf blade are located stomata.
There must be atttttttttttttt
Stoma
- slit hole in the skin (epidermis), surrounded by two guard cells. Serves for gas exchange and transpiration. In the light, with sufficient moisture, the stomata are open, in the dark or with a lack of water, they are closed.
Rice. A-closed, B-open. 1 - guard cells of the stomata, 2 - stomatal slit, 3 - chloroplasts, 4 - adjacent cells of the leaf skin (main epidermis), 5 - thickened cell wall, 6 - thin cell wall.
Mechanism of operation stomata is due to the following structural features of the guard cells: they contain chloroplasts, while the remaining cells of the epidermis do not contain them; guard cells have a thickened wall on the side of the stomatal fissure. In the light, the process of photosynthesis occurs only in the guard cells; the resulting sugars increase the concentration of cell sap, which, due to the laws of osmosis, causes the flow of water into these cells. Turgor pressure increases, and the cells begin to swell, increasing in volume. But this is prevented by the cell wall, especially its thick side facing the stomatal fissure. As a result, the guard cells stretch towards the main epidermis, where the walls are thinner and the thick ones follow the entire cell - the stomata opens. At night, when photosynthesis does not occur, the guard cells return to their place and close - the stomata closes. It was noted that when stomata open, potassium ions move into the guard cells, which also determine an increase in turgor pressure and cell volume
Evaporation in hot weather helps cool the leaves, move water and substances dissolved in it throughout the plant, but if the soil is not sufficiently moistened, it leads to wilting or even death of the plant. There is evaporation of water through the cuticle on the surface of the plant ( cuticular) And stomatal(through stomata).
Under the skin there is chlorophyll-bearing parenchyma ( chlorenchyma ). This tissue forms the pulp of the leaf. This is where the process of photosynthesis occurs. Located under the upper epidermis columnar chlorenchyma(textile). Its cells are elongated, tightly adjacent to each other, and contain many chloroplasts. Typically, chloroplasts are oriented in such a way as to maximize energy use sunlight. The layer of columnar tissue is optimally illuminated, and the process of photosynthesis occurs intensively in it.
Plants grown in bright light conditions usually have two or three layers of columnar tissue called leaves.
In plants grown in the shade, with a lack of light, columnar cells form only one thin layer in the upper part of the leaf - they are called shadow cells.
Under the columnar chlorenchyma (tissue) is spongy chlorenchyma(tissue), the cells of which are round or oblong, contain fewer chloroplasts and are loosely located, since large intercellular spaces filled with air develop between the cells. Spongy tissue is adjacent to the lower epidermis. The process of photosynthesis in spongy tissue is not as intense as in columnar tissue, but the processes of transpiration and gas exchange are active here. The air passes through the stomata, enters the intercellular spaces and travels through them to all leaf tissues. Water in a gaseous state, oxygen and carbon dioxide, formed during photosynthesis and respiration, are collected in the intercellular spaces, and from them are released through the stomata. Thus, both types of assimilative tissue are interconnected into a single complex system.
In the center of the leaf there is a large conductive bundle, and on the side there are smaller bunches. In the upper part of the conducting bundle there are sieve tubes and companion cells. Adjacent to them below are elements of water-conducting fabric - vessels And tracheids. The conducting bundle of the sheet also contains mechanical fabric, which is located either in the form of a closed ring, or in separate sections at the top and bottom. The mechanical fabric strengthens the conductive bundles and gives the sheet mechanical strength.
On the surface of the sheet, conducting bundles clearly appear in the form veins.
The nature of the arrangement of veins in a leaf (venation) is an important systematic feature.
Leaf venation is:
ü arc(lily of the valley leaf);
ü parallel(cereal leaf).
Arc and parallel venation are characteristic of monocotyledonous plants.
Dicotyledonous plants are characterized by reticulate venation:
ü palmate, when all the veins converge at one point at the base of the leaf blade (Tatar maple);
ü feathery, when the central vein is pronounced (leaf of bird cherry, birch).
| Leaf fabric | Structure | Function |
| cover tissue | The upper skin is formed by tightly pressed transparent cells (4) of irregular shape. Often covered cuticle or hairs | Facing the sun, protection from external influences and evaporation |
| The lower skin usually has stomata. The stomata are formed by two guard cells (2), the walls of which are thickened on one side, with a stomatal fissure (1) located between them. Guard cells have chloroplasts (3). | Located on the underside of the sheet. Protection, breathing and evaporation | |
| Main fabric: columnar | Tightly lying cylindrical cells with chloroplasts | Located on the upper side of the sheet. Serves for photosynthesis |
| spongy | Round cells with intercellular spaces forming air cavities contain less chlorophyll | Located closer to the underside of the leaf. Photosynthesis + water and gas exchange |
| Mechanical | Leaf vein (fiber) | Elasticity and strength |
| Conductive | Leaf vein: - vessels | Flow of water and minerals from the root |
| - sieve tubes | Flow of water and organic matter to the stem and root |
Ø C2. What type of leaf is shown in the picture? Which parts of the sheet are indicated in the figure by numbers 1 and 2 and what functions do they perform? 1) a simple leaf with reticulate veins and stipules; 2) 1-leaf blade, performs the functions of photosynthesis, gas exchange, transpiration, and in some plants - vegetative propagation; 3) 2 - veins provide transport of substances and support of the leaf.
