Welcome dear students! Today we are going to learn about Tissues from Class 9 Science. From the last chapter, we recall that all living organisms are made of cells. In unicellular organisms, a single cell performs all basic functions. For example, in Amoeba, a single cell carries out movement, intake of food, gaseous exchange and excretion. But in multi-cellular organisms there are millions of cells. Most of these cells are specialised to carry out specific functions. Each specialised function is taken up by a different group of cells. Since these cells carry out only a particular function, they do it very efficiently. In human beings, muscle cells contract and relax to cause movement, nerve cells carry messages, blood flows to transport oxygen, food, hormones and waste material and so on. In plants, vascular tissues conduct food and water from one part of the plant to other parts. So, multi-cellular organisms show division of labour. Cells specialising in one function are often grouped together in the body. This means that a particular function is carried out by a cluster of cells at a definite place in the body. This cluster of cells, called a tissue, is arranged and designed so as to give the highest possible efficiency of function. Blood, phloem and muscle are all examples of tissues. A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.
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Let us address the questions from page forty seven of your textbook. Question one, what is a tissue? As we just defined, a tissue is a group of cells that are similar in structure and/or work together to achieve a particular function. Question two, what is the utility of tissues in multi-cellular organisms? The utility lies in division of labour. By grouping specialised cells together at definite places, multi-cellular organisms achieve the highest possible efficiency of function, allowing complex tasks like movement, transport, and communication to occur simultaneously and effectively. Now let us move to section six point one, where we ask, are plants and animals made of same types of tissues? Let us compare their structure and functions. There are noticeable differences between the two. Plants are stationary or fixed, they do not move. Since they have to be upright, they have a large quantity of supportive tissue. The supportive tissue generally has dead cells. Animals on the other hand move around in search of food, mates and shelter. They consume more energy as compared to plants. Most of the tissues they contain are living. Another difference between animals and plants is in the pattern of growth. The growth in plants is limited to certain regions, while this is not so in animals. There are some tissues in plants that divide throughout their life. These tissues are localised in certain regions. Based on the dividing capacity of the tissues, various plant tissues can be classified as growing or meristematic tissue and permanent tissue. Cell growth in animals is more uniform. So, there is no such demarcation of dividing and non-dividing regions in animals.
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The structural organisation of organs and organ systems is far more specialised and localised in complex animals than even in very complex plants. This fundamental difference reflects the different modes of life pursued by these two major groups of organisms, particularly in their different feeding methods. Also, they are differently adapted for a sedentary existence on one hand, which is plants, and active locomotion on the other, which is animals, contributing to this difference in organ system design. It is with reference to these complex animal and plant bodies that we will now talk about the concept of tissues in some detail. Let us move to section six point two, Plant Tissues. We begin with six point two point one, Meristematic Tissue. Look at Figure six point one, which shows the growth of roots in onion bulbs. In this diagram, we see two glass jars filled with water. Each jar has an onion bulb placed on top, with roots growing downwards into the water. This visual demonstrates how roots elongate over time. Now, let us perform Activity six point one. Take two glass jars and fill them with water. Now, take two onion bulbs and place one on each jar, as shown in Figure six point one. Observe the growth of roots in both the bulbs for a few days. Measure the length of roots on day one, day two and day three. On day four, cut the root tips of the onion bulb in jar two by about one centimetre. After this, observe the growth of roots in both the jars and measure their lengths each day for five more days. You will record the observations in a table with columns for length, day one, day two, day three, day four, and day five, and rows for jar one and jar two.
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From these observations, answer the following questions. Which of the two onions has longer roots? The onion in jar one will have longer roots because its root tips, which contain the dividing tissue, were not removed. Do the roots continue growing even after we have removed their tips? No, the roots in jar two will stop growing after the tips are removed. Why would the tips stop growing in jar two after we cut them? Because the root tips contain the meristematic tissue responsible for cell division and growth. Removing them halts further elongation. The growth of plants occurs only in certain specific regions. This is because the dividing tissue, also known as meristematic tissue, is located only at these points. Depending on the region where they are present, meristematic tissues are classified as apical, lateral and intercalary. Refer to Figure six point two, which shows the location of meristematic tissue in the plant body. In this diagram, apical meristem is marked at the very tips of the roots and shoots. Intercalary meristem is shown near the nodes, which are the joints along the stem. Lateral meristem is indicated along the sides of the stem and root, running vertically. Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root. The girth of the stem or root increases due to lateral meristem, also known as cambium. Intercalary meristem seen in some plants is located near the node. Cells of meristematic tissue are very active, they have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles. Can we think why they would lack vacuoles? You might want to refer to the functions of vacuoles in the chapter on cells.
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Now we move to six point two point two, Permanent Tissue. What happens to the cells formed by meristematic tissue? They take up a specific role and lose the ability to divide. As a result, they form a permanent tissue. This process of taking up a permanent shape, size, and a function is called differentiation. Differentiation leads to the development of various types of permanent tissues. Let us consider why there would be so many types of cells. We can also try cutting sections of plant roots, or even try cutting sections of root and stem of different plants. This leads us to Activity six point two. Take a plant stem and with the help of your teacher cut into very thin slices or sections. Now, stain the slices with safranin. Place one neatly cut section on a slide, and put a drop of glycerine. Cover with a cover-slip and observe under a microscope. Observe the various types of cells and their arrangement. Compare it with Figure six point three. Figure six point three shows a section of a stem. In this diagram, we see a cross section with several distinct layers. The outermost layer is the epidermis, followed by a thin cuticle. Beneath that is the collenchyma layer, then a large region of parenchyma. In the center, we see vascular bundles containing phloem and xylem. Now answer the following on the basis of your observation. Are all cells similar in structure? No, they differ in shape, wall thickness, and arrangement. How many types of cells can be seen? You can observe epidermal cells, collenchyma cells, parenchyma cells, and vascular tissue cells like xylem and phloem.
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We now study six point two point two part one, Simple Permanent Tissue. A few layers of cells beneath the epidermis are generally simple permanent tissue. Parenchyma is the most common simple permanent tissue. It consists of relatively unspecialised cells with thin cell walls. They are living cells. They are usually loosely arranged, thus large spaces between cells, called intercellular spaces, are found in this tissue. Refer to Figure six point four part a, which shows parenchyma cells. They appear as loosely packed, roughly spherical or oval cells with thin walls and visible nuclei and vacuoles. This tissue generally stores food. In some situations, it contains chlorophyll and performs photosynthesis, and then it is called chlorenchyma. In aquatic plants, large air cavities are present in parenchyma to help them float. Such a parenchyma type is called aerenchyma. The flexibility in plants is due to another permanent tissue, collenchyma. It allows bending of various parts of a plant like tendrils and stems of climbers without breaking. It also provides mechanical support. We can find this tissue in leaf stalks below the epidermis. The cells of this tissue are living, elongated and irregularly thickened at the corners. There is very little intercellular space. Look at Figure six point four part b for collenchyma. It shows elongated cells with noticeably thickened corners and narrow intercellular spaces.
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Yet another type of permanent tissue is sclerenchyma. It is the tissue which makes the plant hard and stiff. We have seen the husk of a coconut. It is made of sclerenchymatous tissue. The cells of this tissue are dead. They are long and narrow as the walls are thickened due to lignin. Often these walls are so thick that there is no internal space inside the cell. Figure six point four part c shows sclerenchyma in transverse and longitudinal sections. The cells appear as long, narrow, dead cells with extremely thick, lignified walls and almost no lumen. This tissue is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts. It provides strength to the plant parts. Let us perform Activity six point three. Take a freshly plucked leaf of Rhoeo. Stretch and break it by applying pressure. While breaking it, keep it stretched gently so that some peel or skin projects out from the cut. Remove this peel and put it in a petri dish filled with water. Add a few drops of safranin. Wait for a couple of minutes and then transfer it onto a slide. Gently place a cover slip over it. Observe under microscope. What you observe is the outermost layer of cells, called epidermis. The epidermis is usually made of a single layer of cells. In some plants living in very dry habitats, the epidermis may be thicker since protection against water loss is critical. The entire surface of a plant has an outer covering epidermis. It protects all the parts of the plant.
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Epidermal cells on the aerial parts of the plant often secrete a waxy, water-resistant layer on their outer surface. This aids in protection against loss of water, mechanical injury and invasion by parasitic fungi. Since it has a protective role to play, cells of epidermal tissue form a continuous layer without intercellular spaces. Most epidermal cells are relatively flat. Often their outer and side walls are thicker than the inner wall. We can observe small pores here and there in the epidermis of the leaf. These pores are called stomata. Refer to Figure six point five, which shows guard cells and epidermal cells in lateral and surface views. In part a, the lateral view shows kidney-shaped guard cells surrounding a pore. In part b, the surface view shows the same arrangement from above, highlighting the stoma opening between two guard cells. Stomata are enclosed by two kidney-shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere. Transpiration, which is the loss of water in the form of water vapour, also takes place through stomata. Recall which gas is required for photosynthesis. It is carbon dioxide. Find out the role of transpiration in plants. It helps in cooling the plant and pulling water and minerals upward from the roots. Epidermal cells of the roots, whose function is water absorption, commonly bear long hair-like parts that greatly increase the total absorptive surface area. In some plants like desert plants, epidermis has a thick waxy coating of cutin, a chemical substance with waterproof quality, on its outer surface. Can we think of a reason for this? It prevents excessive water loss in arid conditions.
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Is the outer layer of a branch of a tree different from the outer layer of a young stem? Yes, it is. As plants grow older, the outer protective tissue undergoes certain changes. A strip of secondary meristem located in the cortex forms layers of cells which constitute the cork. Cells of cork are dead and compactly arranged without intercellular spaces. Look at Figure six point six, which shows protective tissue. The diagram displays tightly packed, dead cork cells with thick walls. They also have a substance called suberin in their walls that makes them impervious to gases and water. Now we move to six point two point two part two, Complex Permanent Tissue. The different types of tissues we have discussed until now are all made of one type of cells, which look like each other. Such tissues are called simple permanent tissue. Yet another type of permanent tissue is complex tissue. Complex tissues are made of more than one type of cells. All these cells coordinate to perform a common function. Xylem and phloem are examples of such complex tissues. They are both conducting tissues and constitute a vascular bundle. Vascular tissue is a distinctive feature of the complex plants, one that has made possible their survival in the terrestrial environment. In Figure six point three showing a section of stem, you can see different types of cells in the vascular bundle.
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Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres. Refer to Figure six point seven parts a, b, and c. Part a shows a tracheid, which is a long, tapered cell with thick walls. Part b shows a vessel, which is a wider, tube-like structure formed by joined cells. Part c shows xylem parenchyma, which are living cells with thin walls. Tracheids and vessels have thick walls, and many are dead cells when mature. Tracheids and vessels are tubular structures. This allows them to transport water and minerals vertically. The parenchyma stores food. Xylem fibres are mainly supportive in function. Phloem is made up of five types of cells: sieve cells, sieve tubes, companion cells, phloem fibres and the phloem parenchyma. Look at Figure six point seven part d, which shows a section of phloem. Sieve tubes are tubular cells with perforated walls. Phloem transports food from leaves to other parts of the plant. Except phloem fibres, other phloem cells are living cells. Let us address the questions on page fifty two. Question one, name types of simple tissues. The types are parenchyma, collenchyma, and sclerenchyma. Question two, where is apical meristem found? It is found at the growing tips of stems and roots. Question three, which tissue makes up the husk of coconut? Sclerenchyma tissue. Question four, what are the constituents of phloem? Sieve cells, sieve tubes, companion cells, phloem fibres, and phloem parenchyma.
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Let us now move to section six point three, Animal Tissues. When we breathe we can actually feel the movement of our chest. How do these body parts move? For this we have specialised cells called muscle cells. Look at Figure six point eight, which shows the location of muscle fibres in the stomach wall. The diagram displays elongated, spindle-shaped smooth muscle fibres arranged in bundles, with visible nuclei. The contraction and relaxation of these cells result in movement. During breathing we inhale oxygen. Where does this oxygen go? It is absorbed in the lungs and then is transported to all the body cells through blood. Why would cells need oxygen? The functions of mitochondria we studied earlier provide a clue to this question. Blood flows and carries various substances from one part of the body to the other. For example, it carries oxygen and food to all cells. It also collects wastes from all parts of the body and carries them to the liver and kidney for disposal. Blood and muscles are both examples of tissues found in our body. On the basis of the functions they perform we can think of different types of animal tissues, such as epithelial tissue, connective tissue, muscular tissue and nervous tissue. Blood is a type of connective tissue, and muscle forms muscular tissue.
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We begin with six point three point one, Epithelial Tissue. The covering or protective tissues in the animal body are epithelial tissues. Epithelium covers most organs and cavities within the body. It also forms a barrier to keep different body systems separate. The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue. Epithelial tissue cells are tightly packed and form a continuous sheet. They have only a small amount of cementing material between them and almost no intercellular spaces. Obviously, anything entering or leaving the body must cross at least one layer of epithelium. As a result, the permeability of the cells of various epithelia play an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body. Regardless of the type, all epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane. Different epithelia show differing structures that correlate with their unique functions. Refer to Figure six point nine, which illustrates different types of epithelial tissues. Part a shows squamous epithelium, which appears as flat, scale-like cells. Part b shows stratified squamous epithelium, with multiple layers of flat cells. Part c shows cuboidal epithelium, composed of cube-shaped cells. Part d shows columnar ciliated epithelium, featuring tall pillar-like cells with hair-like cilia on top.
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For example, in cells lining blood vessels or lung alveoli, where transportation of substances occurs through a selectively permeable surface, there is a simple flat kind of epithelium. This is called the simple squamous epithelium. Squama means scale of skin. Simple squamous epithelial cells are extremely thin and flat and form a delicate lining. The oesophagus and the lining of the mouth are also covered with squamous epithelium. The skin, which protects the body, is also made of squamous epithelium. Skin epithelial cells are arranged in many layers to prevent wear and tear. Since they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium. Where absorption and secretion occur, as in the inner lining of the intestine, tall epithelial cells are present. This columnar, meaning pillar-like, epithelium facilitates movement across the epithelial barrier. In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells. These cilia can move, and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium. Cuboidal epithelium, with cube-shaped cells, forms the lining of kidney tubules and ducts of salivary glands, where it provides mechanical support. Epithelial cells often acquire additional specialisation as gland cells, which can secrete substances at the epithelial surface. Sometimes a portion of the epithelial tissue folds inward, and a multicellular gland is formed. This is glandular epithelium.
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Next is six point three point two, Connective Tissue. Blood is a type of connective tissue. Why would it be called connective tissue? A clue is provided in the introduction of this chapter. The cells of connective tissue are loosely spaced and embedded in an intercellular matrix. Refer to Figure six point ten, which shows types of connective tissues. Part a shows types of blood cells, including red blood corpuscles, various white blood corpuscles like neutrophils, eosinophils, basophils, lymphocytes, monocytes, and platelets. Part b shows compact bone with Haversian canals containing blood vessels and nerve fibres. Part c shows hyaline cartilage with chondrocytes in a hyaline matrix. Part d shows areolar tissue with fibroblasts, macrophages, mast cells, plasma cells, and collagen fibres. Part e shows adipose tissue with large fat droplets inside adipocytes. The matrix may be jelly like, fluid, dense or rigid. The nature of matrix differs in concordance with the function of the particular connective tissue. Let us perform Activity six point four. Take a drop of blood on a slide and observe different cells present in it under a microscope. Blood has a fluid, or liquid, matrix called plasma, in which red blood corpuscles, white blood corpuscles and platelets are suspended. The plasma contains proteins, salts and hormones. Blood flows and transports gases, digested food, hormones and waste materials to different parts of the body.
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Bone is another example of a connective tissue. It forms the framework that supports the body. It also anchors the muscles and supports the main organs of the body. It is a strong and nonflexible tissue. Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds. Two bones can be connected to each other by another type of connective tissue called the ligament. This tissue is very elastic. It has considerable strength. Ligaments contain very little matrix and connect bones with bones. Tendons connect muscles to bones and are another type of connective tissue. Tendons are fibrous tissue with great strength but limited flexibility. Another type of connective tissue, cartilage, has widely spaced cells. The solid matrix is composed of proteins and sugars. Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea and larynx. We can fold the cartilage of the ears, but we cannot bend the bones in our arms. Think of how the two tissues are different. Areolar connective tissue is found between the skin and muscles, around blood vessels and nerves and in the bone marrow. It fills the space inside the organs, supports internal organs and helps in repair of tissues. Where are fats stored in our body? Fat-storing adipose tissue is found below the skin and between internal organs. The cells of this tissue are filled with fat globules. Storage of fats also lets it act as an insulator.
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Now we study six point three point three, Muscular Tissue. Muscular tissue consists of elongated cells, also called muscle fibres. This tissue is responsible for movement in our body. Muscles contain special proteins called contractile proteins, which contract and relax to cause movement. Refer to Figure six point eleven, which shows types of muscle fibres. Part a shows striated muscle, with long, cylindrical, unbranched cells showing alternate light and dark bands, and multiple nuclei at the periphery. Part b shows smooth muscle, with spindle-shaped, unbranched cells, a single central nucleus, and no striations. Part c shows cardiac muscle, with branched, cylindrical cells, a single central nucleus, and visible striations. These muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement. Under the microscope, these muscles show alternate light and dark bands or striations when stained appropriately. As a result, they are also called striated muscles. The cells of this tissue are long, cylindrical, unbranched and multinucleate, meaning having many nuclei. The movement of food in the alimentary canal or the contraction and relaxation of blood vessels are involuntary movements. We cannot really start them or stop them simply by wanting to do so. Smooth muscles, or involuntary muscles, control such movements. They are also found in the iris of the eye, in ureters and in the bronchi of the lungs. The cells are long with pointed ends, which is spindle-shaped, and uninucleate, meaning having a single nucleus. They are also called unstriated muscles. Why would they be called that? Because they lack the visible light and dark bands seen in skeletal muscles.
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The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles. Heart muscle cells are cylindrical, branched and uninucleate. Let us perform Activity six point five. Compare the structures of different types of muscular tissues. Note down their shape, number of nuclei and position of nuclei within the cell in Table six point one. For striated muscle, the shape is long and cylindrical, number of nuclei is many, and position is peripheral. For smooth muscle, the shape is spindle-shaped, number of nuclei is one, and position is central. For cardiac muscle, the shape is cylindrical and branched, number of nuclei is one, and position is central. We move to six point three point four, Nervous Tissue. We can move some muscles by conscious will. Muscles present in our limbs move when we want them to, and stop when we so decide. Such muscles are called voluntary muscles. All cells possess the ability to respond to stimuli. However, cells of the nervous tissue are highly specialised for being stimulated and then transmitting the stimulus very rapidly from one place to another within the body. The brain, spinal cord and nerves are all composed of the nervous tissue. The cells of this tissue are called nerve cells or neurons. A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. Look at Figure six point twelve, which shows a neuron, the unit of nervous tissue.
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The diagram displays a central cell body containing a nucleus. Extending from it are many short, branched dendrites. A single long axon extends away from the cell body, ending in nerve endings. Usually each neuron has a single long part, called the axon, and many short, branched parts called dendrites. An individual nerve cell may be up to a metre long. Many nerve fibres bound together by connective tissue make up a nerve. The signal that passes along the nerve fibre is called a nerve impulse. Nerve impulses allow us to move our muscles when we want to. The functional combination of nerve and muscle tissue is fundamental to most animals. This combination enables animals to move rapidly in response to stimuli. Let us quickly review what you have learnt. Tissue is a group of cells similar in structure and function. Plant tissues are of two main types, meristematic and permanent. Meristematic tissue is the dividing tissue present in the growing regions of the plant. Permanent tissues are derived from meristematic tissue once they lose the ability to divide. They are classified as simple and complex tissues. Parenchyma, collenchyma and sclerenchyma are three types of simple tissues. Xylem and phloem are types of complex tissues. Animal tissues can be epithelial, connective, muscular and nervous tissue. Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated and glandular. The different types of connective tissues in our body include areolar tissue, adipose tissue, bone, tendon, ligament, cartilage and blood. Striated, unstriated and cardiac are three types of muscle tissues. Nervous tissue is made of neurons that receive and conduct impulses.
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Now, let us solve the exercises from the textbook. Question one. Define the term tissue. Answer. A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue. Question two. How many types of elements together make up the xylem tissue? Name them. Answer. Four types of elements make up the xylem tissue. They are tracheids, vessels, xylem parenchyma and xylem fibres. Question three. How are simple tissues different from complex tissues in plants? Answer. Simple tissues are made of only one type of cells which look like each other and perform a common function. Complex tissues are made of more than one type of cells, all of which coordinate to perform a common function. Question four. Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall. Answer. Parenchyma cells have thin cell walls made of cellulose. Collenchyma cells have irregularly thickened cell walls at the corners, made of cellulose and pectin. Sclerenchyma cells have thick walls that are heavily thickened due to lignin, and they are usually dead at maturity. Question five. What are the functions of the stomata? Answer. The functions of stomata are to facilitate the exchange of gases with the atmosphere and to allow transpiration, which is the loss of water in the form of water vapour. Question six. Diagrammatically show the difference between the three types of muscle fibres. Answer. Since this is an audio lesson, I will describe the diagrammatic differences. Striated muscle fibres are long, cylindrical, unbranched, show alternate light and dark bands, and are multinucleate with nuclei at the periphery. Smooth muscle fibres are spindle-shaped, unbranched, lack striations, and are uninucleate with a central nucleus. Cardiac muscle fibres are cylindrical, branched, show faint striations, and are uninucleate with a central nucleus.
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Question seven. What is the specific function of the cardiac muscle? Answer. The specific function of cardiac muscle is to show rhythmic contraction and relaxation throughout life, which pumps blood continuously. Question eight. Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site or location in the body. Answer. Striated muscles are long, cylindrical, unbranched, multinucleate, and attached to bones in limbs. Unstriated muscles are spindle-shaped, uninucleate, and found in the alimentary canal, blood vessels, iris of the eye, ureters, and bronchi. Cardiac muscles are cylindrical, branched, uninucleate, and found exclusively in the heart. Question nine. Draw a labelled diagram of a neuron. Answer. In an audio format, I will describe it. A neuron consists of a central cell body containing a nucleus and cytoplasm. Short, branched processes called dendrites extend from the cell body. A single long process called the axon extends from the opposite end, terminating in nerve endings. Question ten. Name the following. Part a. Tissue that forms the inner lining of our mouth. Answer. Squamous epithelium. Part b. Tissue that connects muscle to bone in humans. Answer. Tendon. Part c. Tissue that transports food in plants. Answer. Phloem. Part d. Tissue that stores fat in our body. Answer. Adipose tissue. Part e. Connective tissue with a fluid matrix. Answer. Blood. Part f. Tissue present in the brain. Answer. Nervous tissue. Question eleven. Identify the type of tissue in the following: skin, bark of tree, bone, lining of kidney tubule, vascular bundle. Answer. Skin is made of stratified squamous epithelium. Bark of tree is made of cork, a protective tissue. Bone is a connective tissue. Lining of kidney tubule is made of cuboidal epithelium. Vascular bundle is a complex permanent tissue.
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Question twelve. Name the regions in which parenchyma tissue is present. Answer. Parenchyma tissue is present in the cortex of stems and roots, in the pith, in the mesophyll of leaves, and in the ground tissue of plants. It is also found in the vascular bundles as xylem and phloem parenchyma. Question thirteen. What is the role of epidermis in plants? Answer. The epidermis forms the outermost protective layer of the plant. It protects against water loss, mechanical injury, and invasion by parasitic fungi. In roots, it bears root hairs for water absorption. In leaves, it contains stomata for gas exchange and transpiration. Question fourteen. How does the cork act as a protective tissue? Answer. Cork acts as a protective tissue because its cells are dead, compactly arranged without intercellular spaces, and their walls contain suberin, which makes them impervious to gases and water, thus preventing water loss and protecting against mechanical injury and pathogens. Question fifteen. Complete the following chart. The chart classifies permanent tissue into simple and complex. Under simple, it lists collenchyma, and the other two are parenchyma and sclerenchyma. Under complex, it lists xylem, and the other one is phloem. So the completed chart is: Permanent tissue divides into simple and complex. Simple includes parenchyma, collenchyma, and sclerenchyma. Complex includes xylem and phloem.
Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]