Chapter 6 Tissues PDF

C hapter 6 TISSUES From the last chapter, we recall that all living There are noticeable differences between organisms are made of cells. In unicellular the two. Plants are stationary or fixed...

C hapter 6 TISSUES From the last chapter, we recall that all living There are noticeable differences between organisms are made of cells. In unicellular the two. Plants are stationary or fixed – they organisms, a single cell performs all basic don’t move. Since they have to be upright, they functions. For example, in Amoeba, a single have a large quantity of supportive tissue. The cell carries out movement, intake of food, supportive tissue generally has dead cells. gaseous exchange and excretion. But in multi- Animals on the other hand move around cellular organisms there are millions of cells. in search of food, mates and shelter. They Most of these cells are specialised to carry out consume more energy as compared to plants. specific functions. Each specialised function Most of the tissues they contain are living. is taken up by a different group of cells. Since Another difference between animals and these cells carry out only a particular function, they do it very efficiently. In human beings, plants is in the pattern of growth. The growth muscle cells contract and relax to cause in plants is limited to certain regions, while this movement, nerve cells carry messages, blood is not so in animals. There are some tissues in flows to transport oxygen, food, hormones and plants that divide throughout their life. These waste material and so on. In plants, vascular tissues are localised in certain regions. Based tissues conduct food and water from one part on the dividing capacity of the tissues, various of the plant to other parts. So, multi-cellular plant tissues can be classified as growing or organisms show division of labour. Cells meristematic tissue and permanent tissue. Cell specialising in one function are often grouped growth in animals is more uniform. So, there together in the body. This means that a is no such demarcation of dividing and non- particular function is carried out by a cluster dividing regions in animals. of cells at a definite place in the body. This The structural organisation of organs and cluster of cells, called a tissue, is arranged and organ systems is far more specialised and designed so as to give the highest possible localised in complex animals than even in very efficiency of function. Blood, phloem and muscle are all examples of tissues. complex plants. This fundamental difference A group of cells that are similar in structure reflects the different modes of life pursued by and/or work together to achieve a particular these two major groups of organisms, function forms a tissue. particularly in their different feeding methods. Also, they are differently adapted for a 6.1 Are Plants and Animals Made sedentary existence on one hand (plants) and active locomotion on the other (animals), of Same Types of Tissues? contributing to this difference in organ system Let us compare their structure and functions. design. Do plants and animals have the same It is with reference to these complex animal structure? Do they both perform similar and plant bodies that we will now talk about functions? the concept of tissues in some detail. 2024-25 Q From the above observations, answer uestions the following questions: 1. What is a tissue? 1. Which of the two onions has longer 2. What is the utility of tissues in roots? Why? 2. Do the roots continue growing multi-cellular organisms? even after we have removed their tips? 3. Why would the tips stop growing in jar 2 after we cut them? 6.2 Plant Tissues The growth of plants occurs only in certain 6.2.1 MERISTEMATIC TISSUE 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 (Fig. 6.2). New cells produced by meristem are initially like those of meristem itself, but as they grow and mature, their characteristics slowly change and they become differentiated as components of other tissues. Apical meristem Jar 1 Jar 2 Fig. 6.1: Growth of roots in onion bulbs Intercalary meristem Activity ______________ 6.1 Take two glass jars and fill them with water. Now, take two onion bulbs and place one on each jar, as shown in Fig. 6.1. Observe the growth of roots in both the bulbs for a few days. Measure the length of roots on day 1, 2 and 3. On day 4, cut the root tips of the onion bulb in jar 2 by about 1 cm. After this, Lateral meristem observe the growth of roots in both the jars and measure their lengths each day for five more days and record the observations in tables, like the table Fig. 6.2: Location of meristematic tissue in plant body below: Apical meristem is present at the growing tips of stems and roots and increases the Length Day 1 Day 2 Day 3 Day 4 Day 5 length of the stem and the root. The girth of the stem or root increases due to lateral Jar 1 meristem (cambium). Intercalary meristem Jar 2 seen in some plants is located near the node. TISSUES 61 2024-25  Cells of meristematic tissue are very active, 3. Can we think of reasons why there they have dense cytoplasm, thin cellulose walls would be so many types of cells? and prominent nuclei. They lack vacuoles. Can We can also try to cut sections of plant we think why they would lack vacuoles? (You roots. We can even try cutting sections might want to refer to the functions of vacuoles of root and stem of different plants. in the chapter on cells.) 6.2.2 (i) SIMPLE PERMANENT TISSUE 6.2.2 PERMANENT TISSUE A few layers of cells beneath the epidermis are What happens to the cells formed by generally simple permanent tissue. meristematic tissue? They take up a specific Parenchyma is the most common simple role and lose the ability to divide. As a result, permanent tissue. It consists of relatively they form a permanent tissue. This process unspecialised cells with thin cell walls. They of taking up a permanent shape, size, and a are living cells. They are usually loosely function is called differentiation. Differentiation arranged, thus large spaces between cells leads to the development of various types of (intercellular spaces) are found in this tissue permanent tissues. (Fig. 6.4 a). This tissue generally stores food. Cuticle Epidermis Collenchyma Parenchyma Phloem Xylem Vascular bundle Fig. 6.3: Section of a stem Activity ______________ 6.2 In some situations, it contains chlorophyll and performs photosynthesis, and then it is called Take a plant stem and with the help chlorenchyma. In aquatic plants, large air of your teacher cut into very thin slices cavities are present in parenchyma to help or sections. them float. Such a parenchyma type is called Now, stain the slices with safranin. aerenchyma. Place one neatly cut section on a slide, The flexibility in plants is due to another and put a drop of glycerine. permanent tissue, collenchyma. It allows Cover with a cover-slip and observe bending of various parts of a plant like tendrils under a microscope. Observe the and stems of climbers without breaking. It various types of cells and their also provides mechanical support. We can find arrangement. Compare it with Fig. 6.3. this tissue in leaf stalks below the epidermis. Now, answer the following on the The cells of this tissue are living, elongated basis of your observation: 1. Are all cells similar in structure? and irregularly thickened at the 2. How many types of cells can corners. There is very little intercellular space be seen? (Fig. 6.4 b). 62 SCIENCE 2024-25  Intercellular spaces Wall thickenings Nucleus Thick lignified Vacuole walls Narrow lumen Cell wall Lignified thick wall a b c (i) c (ii) Fig. 6.4: Various types of simple tissues: (a) Parenchyma (b) Collenchyma (c) Sclerenchyma (i) transverse section, (ii) longitudinal section. 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 Guard due to lignin. Often these walls are so thick cells that there is no internal space inside the cell Stoma (Fig. 6.4 c). This tissue is present in stems, Epidermal around vascular bundles, in the veins of leaves cell Guard and in the hard covering of seeds and nuts. It cell provides strength to the plant parts. (a) (b) Activity ______________ 6.3 Fig. 6.5: Guard cells and epidermal cells: (a) lateral Take a freshly plucked leaf of Rhoeo. view, (b) surface view Stretch and break it by applying pressure. parts of the plant often secrete a waxy, water- While breaking it, keep it stretched resistant layer on their outer surface. This aids gently so that some peel or skin in protection against loss of water, mechanical projects out from the cut. Remove this peel and put it in a petri injury and invasion by parasitic fungi. Since dish filled with water. it has a protective role to play, cells of Add a few drops of safranin. epidermal tissue form a continuous layer Wait for a couple of minutes and then without intercellular spaces. Most epidermal transfer it onto a slide. Gently place cells are relatively flat. Often their outer and a cover slip over it. side walls are thicker than the inner wall. Observe under microscope. We can observe small pores here and What you observe is the outermost layer there in the epidermis of the leaf. These pores of cells, called epidermis. The epidermis is are called stomata (Fig. 6.5). Stomata are usually made of a single layer of cells. In some enclosed by two kidney-shaped cells plants living in very dry habitats, the epidermis called guard cells. They are necessary for may be thicker since protection against water exchanging gases with the atmosphere. loss is critical. The entire surface of a plant has Transpiration (loss of water in the form of an outer covering epidermis. It protects all the water vapour) also takes place parts of the plant. Epidermal cells on the aerial through stomata. TISSUES 63 2024-25  is a distinctive feature of the complex plants, Recall which gas is required for photosynthesis. one that has made possible their survival in Find out the role of transpiration in plants. the terrestrial environment. In Fig. 6.3 showing a section of stem, can you see different types Epidermal cells of the roots, whose function of cells in the vascular bundle? is water absorption, commonly bear long hair- Xylem consists of tracheids, vessels, xylem like parts that greatly increase the total parenchyma (Fig. 6.7 a,b,c) and xylem fibres. absorptive surface area. Tracheids and vessels have thick walls, and In some plants like desert plants, many are dead cells when mature. Tracheids epidermis has a thick waxy coating of cutin and vessels are tubular structures. This allows (chemical substance with waterproof quality) them to transport water and minerals on its outer surface. Can we think of a reason vertically. The parenchyma stores food. Xylem for this? fibres are mainly supportive in function. Is the outer layer of a branch of a tree Phloem is made up of five types of cells: different from the outer layer of a young stem? sieve cells, sieve tubes, companion cells, As plants grow older, the outer protective phloem fibres and the phloem parenchyma tissue undergoes certain changes. A strip of [Fig. 6.7 (d)]. Sieve tubes are tubular cells with secondary meristem located in the cortex forms perforated walls. Phloem transports food from layers of cells which constitute the cork. Cells leaves to other parts of the plant. Except of cork are dead and compactly arranged phloem fibres, other phloem cells are living cells. without intercellular spaces (Fig. 6.6). They also have a substance called suberin in their walls that makes them impervious to gases and water. Nucleus Cork cells Ruptured epidermis Pit Pits Cytoplasm (a) Tracheid (b) Vessel (c) Xylem parenchyma Fig. 6.6: Protective tissue 6.2.2 (ii) COMPLEX PERMANENT TISSUE Sieve plate Sieve tube 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 Phloem called simple permanent tissue. Yet another parenchyma type of permanent tissue is complex tissue. Companion cell 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 (d) Section of phloem constitute a vascular bundle. Vascular tissue Fig. 6.7: Types of complex tissue 64 SCIENCE 2024-25  uestions Q During breathing we inhale oxygen. Where does this oxygen go? It is absorbed in the lungs 1. Name types of simple tissues. and then is transported to all the body cells 2. Where is apical meristem found? through blood. Why would cells need oxygen? 3. Which tissue makes up the husk The functions of mitochondria we studied of coconut? earlier provide a clue to this question. Blood 4. What are the constituents of flows and carries various substances from one phloem? 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 6.3 Animal Tissues carries them to the liver and kidney for disposal. When we breathe we can actually feel the Blood and muscles are both examples of movement of our chest. How do these body tissues found in our body. On the basis of the parts move? For this we have specialised cells functions they perform we can think of different called muscle cells (Fig. 6.8). The contraction types of animal tissues, such as epithelial and relaxation of these cells result tissue, connective tissue, muscular tissue and in movement. nervous tissue. Blood is a type of connective tissue, and muscle forms muscular tissue. 6.3.1 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 Smooth muscle fibres epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane. Nucleus Different epithelia (Fig. 6.9) show differing Smooth muscle fibre structures that correlate with their unique functions. For example, in cells lining blood (Cell) vessels or lung alveoli, where transportation of substances occurs through a selectively Fig. 6.8: Location of muscle fibres permeable surface, there is a simple flat kind TISSUES 65 2024-25 of epithelium. This is called the simple of skin). Simple squamous epithelial cells are squamous epithelium (squama means scale 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 (a) Squamous 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 (b) Stratified squamous 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. 6.3.2 CONNECTIVE TISSUE Blood is a type of connective tissue. Why would it be called ‘connective’ tissue? A clue is (c) Cuboidal provided in the introduction of this chapter! Now, let us look at this type of tissue in some more detail. The cells of connective tissue are loosely spaced and embedded in an intercellular matrix (Fig. 6.10). 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. Activity 6.4 (d) Columnar (Ciliated) Take a drop of blood on a slide and observe different cells present in it Fig. 6.9: Different types of epithelial tissues under a microscope. 66 SCIENCE 2024-25  Cytoplasm Blood has a fluid (liquid) matrix called Nucleus plasma, in which red blood corpuscles (RBCs), white blood corpuscles (WBCs) and platelets Neutrophil Eosinophil Basophil are suspended. The plasma contains proteins, Different white (polynuclear leucocyte) salts and hormones. Blood flows and blood corpuscles transports gases, digested food, hormones and waste materials to different parts of the body. Bone is another example of a connective Lymphocyte Monocyte Platelets (a) tissue. It forms the framework that supports Haversian canal the body. It also anchors the muscles and (contains blood vessels Chondrocyte supports the main organs of the body. It is a and nerve fibres) strong and nonflexible tissue (what would be Hyaline matrix the advantage of these properties for bone functions?). Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds. Canaliculus (contains (c) Two bones can be connected to each other slender process of bone cell or osteocyte) by another type of connective tissue called the (b) ligament. This tissue is very elastic. It has Red blood corpuscle considerable strength. Ligaments contain very little matrix and connect bones with Reticular fibre Fibroblast 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. Macrophage Cartilage smoothens bone surfaces at joints and is also present in the nose, ear, trachea Collagen fibre and larynx. We can fold the cartilage of the ears, Mast cell Plasma cell (d) but we cannot bend the bones in our arms. Nucleus Think of how the two tissues are different! Fat droplet 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. Adipocyte (e) 6.3.3 MUSCULAR TISSUE Fig. 6.10: Types of connective tissues: (a) types of blood Muscular tissue consists of elongated cells, cells, (b) compact bone, (c) hyaline cartilage, also called muscle fibres. This tissue is (d) areolar tissue, (e) adipose tissue responsible for movement in our body. TISSUES 67 2024-25 Muscles contain special proteins called [Fig. 6.11(a)]. These muscles are also called contractile proteins, which contract and relax skeletal muscles as they are mostly attached to cause movement. to bones and help in body movement. Under Nuclei the microscope, these muscles show alternate light and dark bands or striations when Striations stained appropriately. As a result, they are also called striated muscles. The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei). (a) The movement of food in the alimentary canal or the contraction and relaxation of blood Spindle shaped vessels are involuntary movements. We cannot muscle cell really start them or stop them simply by wanting to do so! Smooth muscles [Fig. 6.11(b)] 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 (spindle-shaped) and uninucleate (having a single nucleus). They are also called unstriated muscles – why would they be called that? Nucleus The muscles of the heart show rhythmic (b) contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles [Fig. 6.11(c)]. Heart muscle cells are cylindrical, branched and uninucleate. Striations Activity 6.5 Compare the structures of different types of muscular tissues. Note down their shape, number of nuclei and Nuclei position of nuclei within the cell in the Table 6.1. Table 6.1: Features Striated Smooth Cardiac Shape Number of nuclei (c) Position of nuclei Fig. 6.11: Types of muscles fibres: (a) striated muscle, (b) smooth muscle, (c) cardiac muscle 6.3.4 NERVOUS TISSUE We can move some muscles by conscious will. Muscles present in our limbs move when All cells possess the ability to respond to we want them to, and stop when we so decide. stimuli. However, cells of the nervous tissue Such muscles are called voluntary muscles are highly specialised for being stimulated and 68 SCIENCE 2024-25 then transmitting the stimulus very rapidly (processes) called dendrites. An individual from one place to another within the body. The nerve cell may be up to a metre long. Many brain, spinal cord and nerves are all composed nerve fibres bound together by connective of the nervous tissue. The cells of this tissue tissue make up a nerve. are called nerve cells or neurons. A neuron The signal that passes along the nerve fibre consists of a cell body with a nucleus and is called a nerve impulse. Nerve impulses allow cytoplasm, from which long thin hair-like us to move our muscles when we want to. The parts arise (Fig. 6.12). Usually each neuron functional combination of nerve and muscle has a single long part (process), called the tissue is fundamental to most animals. This axon, and many short, branched parts combination enables animals to move rapidly in response to stimuli. Nucleus uestions Q Dendrite 1. Name the tissue responsible for movement in our body. Axon Nerve ending 2. What does a neuron look like? 3. Give three features of cardiac muscles. Cell body 4. What are the functions of Fig. 6.12: Neuron-unit of nervous tissue areolar tissue? 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. TISSUES 69 2024-25  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. Exercises 1. Define the term “tissue”. 2. How many types of elements together make up the xylem tissue? Name them. 3. How are simple tissues different from complex tissues in plants? 4. Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall. 5. What are the functions of the stomata? 6. Diagrammatically show the difference between the three types of muscle fibres. 7. What is the specific function of the cardiac muscle? 8. Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site/location in the body. 9. Draw a labelled diagram of a neuron. 10. Name the following. (a) Tissue that forms the inner lining of our mouth. (b) Tissue that connects muscle to bone in humans. (c) Tissue that transports food in plants. (d) Tissue that stores fat in our body. (e) Connective tissue with a fluid matrix. (f) Tissue present in the brain. 11. Identify the type of tissue in the following: skin, bark of tree, bone, lining of kidney tubule, vascular bundle. 70 SCIENCE 2024-25  12. Name the regions in which parenchyma tissue is present. 13. What is the role of epidermis in plants? 14. How does the cork act as a protective tissue? 15. Complete the following chart: TISSUES 71 2024-25