Tissues - Class Notes PDF

CLASS 9 - SCIENCE TISSUES NOTES: All living organisms are composed of cells. A single cell performs all the basic functions in a unicellular organism while in multicellular organisms, different functions are performed by different cells. What is a tissue? ➔ The group of cells similar in struc...

CLASS 9 - SCIENCE TISSUES NOTES: All living organisms are composed of cells. A single cell performs all the basic functions in a unicellular organism while in multicellular organisms, different functions are performed by different cells. What is a tissue? ➔ The group of cells similar in structure which work together to achieve a particular function forms a tissue. ➔ A tissue may be simple or complex type. ➔ Several tissues are organized to form tissue systems which further form the organs and several organs into organisms. The structural and functional organisation of cells in plants and animals is different. Plants remain stationary, while animals move as per their needs. DIFFERENCE BETWEEN : PLANT TISSUE ANIMAL TISSUE Dead supportive tissues are more Living supportive tissues are more as compared to living tissues. as compared to dead tissues. They require less maintenance They require more maintenance energy. energy. Differentiation of meristematic No differentiation of meristematic and permanent tissue. and permanent tissue. Organisation is easy. Organisation is relatively complex. Tissue organisation is meant for Tissue organisation is meant for high stationary habitat of plants. mobility of animals. PLANT TISSUES Plant tissues can be classified into two types on the basis of their dividing capacity. 1) Meristematic Tissue : Cells are capable of division 2) Permanent Tissue : Mature cells which are not capable of cell division 1) MERISTEMATIC TISSUE ➔ The tissues in which cells always keep dividing and give rise to new cells are called meristematic tissues. ➔ These tissues are responsible for the growth of plants. ➔ Plants grow only in those regions where meristematic tissues are present. CHARACTERISTICS OF MERISTEMATIC TISSUE ➔ Ability to divide themselves and form new tissues. ➔ Cells of meristematic tissues are very active. ➔ It has a thin cell wall made up of cellulose. ➔ It contains dense cytoplasm and prominent nuclei. Meristematic tissue is classified on the basis of their position in the plant body, which are described below: A) APICAL MERISTEM ➔ It is present at the growing tips of stems and roots. ➔ It enables the roots and stem to grow by increasing the length of the plant. B) INTERCALARY MERISTEM ➔ They are located at the base of the leaves or at the internodes. ➔ It helps in elongation of plants. C) LATERAL MERISTEM ➔ They are present on the lateral side of the stems and roots. ➔ It helps to increase the girth of the stem and root.  2) PERMANENT TISSUE ➔ Permanent tissues are derived from the meristematic tissues that take up a specific role and lose their ability to divide. ➔ The process by which the cells of the meristematic tissues get converted into permanent tissue by taking a fixed shape,size and function is called differentiation. Permanent tissues are further divided as : a) Simple Permanent Tissue b) Complex Permanent Tissue A) SIMPLE PERMANENT TISSUE: These tissues are composed of cells which are structurally and functionally similar. Simple Permanent Tissues are of three types : 1) Parenchyma: ➔ It is the most common simple permanent tissue. ➔ These are simple living cells with little specialisation and thin cell walls. ➔ The cells in this type of tissue are loosely arranged, with large intercellular spaces between them. Functions of Parenchyma: ➔ It serves as a food storage tissue. ➔ It provides support to the plants. Parenchyma are of two types: When the parenchyma cell contains chlorophyll in some situations, it performs photosynthesis, such a type of parenchyma is called chlorenchyma. Parenchyma with large air cavities which helps the aquatic plants to float are known as aerenchyma. 2) Collenchyma: ➔ The cells of this tissue are living, elongated and irregularly thickened at the corners. ➔ There is very little intercellular space. ➔ They are found below the epidermis in leaf stalks. Functions of Collenchyma: ➔ It provides mechanical support and flexibility to plants. ➔ It allows bending of various parts (tendrils and stems of climbers) of plants without breaking. 3) Sclerenchyma: ➔ The cells of this tissue are dead, long and narrow. ➔ The walls are thickened due to lignin deposition. ➔ The cells are closely packed and there is no intercellular space. ➔ It is present in stems around vascular bundles, in the veins of leaves and in the hard covering of nuts and seeds. Functions of Sclerenchyma: ➔ It is the tissue which provides strength to the plant and also makes the plant hard and stiff. e.g., husk of coconut is made up of this tissue. ➔ It forms a protective covering around seeds and nuts. PROTECTIVE TISSUE The two types of protective tissues present in plants are: 1) Epidermis: ➔ Cells of epidermal tissue form a continuous layer without intercellular spaces as it has a protective role to play. ➔ Most epidermal cells are relatively flat. ➔ Epidermis aids in the protection against loss of water, mechanical injury and invasion by parasitic fungi. ➔ Epidermis of the leaf contains small pore called stomata. These are enclosed by two kidney shaped cells called guard cells. Two main functions of stomata: 1) They are necessary for exchanging gases in the atmosphere. 2) Process of transpiration (loss of water in the form of water vapour) in plants also takes place through stomata. 2) Cork: ➔ Cells of cork are dead and compactly arranged without intercellular spaces. ➔ They appear at the periphery of roots and stems when they grow older and act as outer protective tissue. ➔ Cell walls of cork cells contain a substance called suberin which makes them impervious to gases and water. B) COMPLEX PERMANENT TISSUE: Complex permanent tissue are made up of different types of cells. These different types of cells coordinate with each other and perform common functions. There are two types of complex permanent tissue: a) Xylem b) Phloem  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. a) XYLEM: ➔ It is responsible for the transport of water and minerals from roots to other parts of the plant. ➔ Xylem is made up of dead cells with thick cell lining. It is composed of : 1) Tracheids: These are dead, long, tubular structures with tapering ends. They transport water and minerals vertically. 2) Vessels: These are long, tube-like structures placed end to end and help in conduction of water. 3) Xylem Parenchyma: These are the only living cells of xylem with thin cell walls. They store food. 4) Xylem Fibres: These are elongated dead cells with tapering ends thick cell walls. b) PHLOEM: ➔ Phloem is made up of living cells. ➔ It allows movement of food from leaves to other parts of the plants. It is composed of : 1) Sieve tubes: These are tubular cells with perforated walls. 2) Sieve cells: These are long conducting cells in the phloem. 3) Companion cells: These are small elongated cells having thin cell walls which are not perforated and have active cytoplasm. They help sieve tubes in translocation of food. 4) Phloem fibres: These are thick walled sclerenchyma cells which provide mechanical strength to the tissue. 5) Phloem Parenchyma: These are thin-walled cells which help in storage of food. Except phloem fibres, other phloem cells are living cells. ANIMAL TISSUES : Animal tissues are classified into four basic types, on the basis of their functions:  1.EPITHELIAL TISSUE ➔ They are the protective tissues of the human body. ➔ Epithelium covers most organs and cavities within the body. ➔ The epithelial tissues are found in the lining of the mouth, in the lining of the blood vessels, skin, lung alveoli and kidney tubules. Structure and functions of epithelial tissue: ➔ It acts as a barrier and separates different organs and systems from each other. ➔ No intercellular space is observed. ➔ The cells are permeable which makes it possible to exchange the materials between the body and the external environment and also between different parts of the body. ➔ The epithelial tissues remain separated from the tissues beneath them because of a thin membrane over them. ➔ On the basis of shape of the cells and their arrangements, epithelial tissues are further classified as follows: i) Squamous Epithelium: It constitutes the skin which protects the body. It is further divided into two types: a) Simple Squamous epithelium : ➔ They have a delicate cell lining and possess extremely thin and flat structure. ➔ The transportation of materials occurs through a selectively permeable surface. ➔ They are found in the lining of blood vessels and lung alveoli, oesophagus and lining of mouth. b) Stratified Squamous epithelium : ➔ It is found in the outer side of the skin. ➔ The cells of skin epithelial are arranged in many layers in order to prevent wear and tear.  ➔ Since they are arranged in patterns of layers, it is called stratified squamous epithelium. ii) Columnar Epithelium: ➔ Columnar epithelial cells contain cylindrical cells and facilitate movement across the epithelial barrier. ➔ They are found in the lining of intestine and stomach. Columnar Epithelial tissue with cilia is known as ciliated columnar epithelium. These cilia (hair-like projections) can move and their movement pushes the mucus forward to clear it. It is found in respiratory tract, kidney tubules,etc. iii) Cuboidal Epithelium: ➔ Cuboidal epithelial cells are formed of cube-shaped cells and contain round nuclei. ➔ They provide mechanical support and also helps in absorption,secretion and excretion of materials. ➔ They are found in the lining of kidney tubules and salivary glands. iv) Glandular Epithelium: ➔ Sometimes, a portion of epithelial tissue folds inward and a multicellular gland is formed which can secrete substances at the epithelial surface. It is known as glandular epithelium. 2.CONNECTIVE TISSUE: ➔ Connective tissues are fibrous in nature. ➔ They are loosely bound cells present in an intercellular matrix. ➔ The matrix can be of various types: Dense, rigid or fluid like. ➔ The nature of the matrix depends on the functionality of the connective tissue. ➔ This tissue is specialised to connect various body organs with each other. E.g., it connects two or more to each other, muscles to bones and binds different tissues together Various types of connective tissues are: 1) Blood 2) Bone 3) Ligaments 4) Tendon 5) Areolar 6)Adipose  Areolar connective tissue: It is found between the skin and muscles, around blood vessels and nerves and in the bone marrow. It supports internal organs and helps in repair of tissues. Adipose tissue: It contains cells that are filled with fat globules. It is called fat-storing tissue and it acts as an insulator. 3.MUSCULAR TISSUE: ➔ It is made up of elongated cells which are known as muscle fibers. ➔ This tissue is responsible for movement in our body. ➔ Muscles contain special proteins called contractile proteins. ➔ These proteins cause relaxation and contraction of the muscles. Different types of muscular tissues are: 1) Skeletal muscle, 2) Smooth muscle and 3) Cardiac Muscle  4.NERVOUS TISSUE: How do we react to stimuli? ➔ It is because of the nervous tissues present in our body. ➔ They are capable of transmitting information quickly from the brain to different parts of the body and vice-versa. ➔ Nervous tissues are found in nerves, brain and spinal cord. ➔ The nervous tissue is composed of cells which are known as nerve cells or neurons. ➔ Neurons connect together to form nerves in our body. Structure of Neuron: A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. Each neuron has a single long part called the axon and many short, branched parts known as dendrites. A nerve cell can be upto 1 metre long.