Tissues PDF

TISSUES Tissues – A group of cells similar in structure that work together to achieve a particular function forms a tissue. All cells of a tissue have common origin. Cells in a tissue are arranged and designed to give the highest possib...

TISSUES Tissues – A group of cells similar in structure that work together to achieve a particular function forms a tissue. All cells of a tissue have common origin. Cells in a tissue are arranged and designed to give the highest possible efficiency of the function they perform. The term tissue was coined by Bichat in 1972. Study of tissues is called histology. (histos = tissue; logos = study) Plant Tissues 1. Meristematic tissues (Meristem) – i. The tissues in which cells always keep dividing to give rise to new cells are called meristematic tissues. ii. Meristematic tissues are responsible for growth of plants. So these are called growth tissues. iii. Plants grow only in those regions where meristematic tissues are present, e.g., root and shoot tip. iv. The cells of meristematic tissue have thin cell walls, dense cytoplam and a large nucleus but lack in vacuoles or contain few vacuoles. v. The meristematic cells do not contain any intercellular space between them. vi. The new cell produced by meristem are initially like those of meristem. Their characteristic change when they grow. vii. Meristematic tissue is classified into 3 parts – (a) Apical Tissue (b) Intercalary Tissue (C) Lateral Meristem (Cambium)  TISSUES a) Apical Tissue- 1) These are present at growing tips of stems and roots. 2) These tissues are help in increase in the length of the stems and the roots. 3) Apical meristem tissues give rise to intercalary and lateral meristem tissues. b) Intercalary Tissues- 1) These are present at the base of the leaves or internodes of twigs, e.g., stems of grass. 2) It helps in longitudinal growth of plants. c) Lateral meristem (cambium)- 1) These are present on the lateral sides of the stems and roots. 2) It helps in increasing the girth of stem and root. 2. Permanent Tissues – i. Permanent tissues are formed when meristematic tissues lose their ability to divide. ii. In this process meristematic tissues have attained a permanent shape, size and function by the process called differentiation. iii. Due to the process of diferentiaton, the meristematic tissues formed various types of permanent tissues. iv. Types of permanent tissues- Simple and Complex permanent tissues. A. Simple Permanent Tissues- A few layers of cells beneath the epidermis are generally simple permanent tissue. These tissues are made type of same type of cells which are structurally and functionally similar. Simple permanent tissues are further divided into 3 types- i) Parenchyma ii) Collenchyma iii) Sclerenchyma i. Parenchyma- a. These are unspecialised living cells and can divide. b. The cell wall is thin and have large vacuoles. c. These have large intercellular space between them, so these are loosely packed. d. These cells are present in the soft part of the plant such as cortex of roots, ground tissues in stems and mesophyll of leaves. FUNCTIONS- 1. Parenchyma serves as food storage tissues. 2. These tissues provide support to plants. 3. The lintercellular space between these cells allow gaseous exchange. 4. These tissues store waste products of plants such as tannin, gum, crystals, resins etc. 5. If chloroplast is present, the parenchyma tissue is called chlorenchyma and it performs photosynthesis.  TISSUES 6. In aquatic plants, large air cavities are present in parenchyma to give buoyancy to the plants. Such type of parenchyma are called aerenchyma. ii. Collenchyma- a. These tissues contain living cells and elongated in shape. b. These tissues are generally found in leaf stalks (petiole) below epidermis and leaf midrib but absent in stems, roots and leaves. c. Cell in these tissues have very little or no intercellular space between them. d. Some of the collenchyma cells contain a few chloroplast. e. Cells are irregularly thickened at the corner due to the deposition of extra cellulose(pectin). FUNCTIONS- 1. It provides mechanical support and flexibility to plants. 2. It allows bending of various parts of plants like tendrils and stems of climber without breaking. 3. When collenchyma contain some cloroplast, they manufacture sugar and starch. iii. Sclerenchyma- a. These tissues contain dead cells and long and narrow in shape. b. The cell wall of sclerenchyma are thick due to the diposition of lignin. c. Due to the thick cell wall, there are no intercellular spaces. d. These tissues are present in stems(around vascular bundles), in the veins of leaves and in the hard covering of seeds and nuts. e. Middle lamella between two sclerenchymatous cells is thin. FUNCTIONS- 1. Its main function is to provide mechanical and protective support, which makes plant hard and stiff. E.g., husk of coconut. 2. It forms protective covering around seeds and nuts. 3. It gives rigidity, flexibility and elasticity to the plant body.  TISSUES Protective tissues- The protective tissue is meant to provide protection to the plants from undue loss of water to retain adequate water in them. There are 2 types of protective tissues present in plants- a) Epidermis, b) Cork (phellem) a) Epidermis- The outermost layer of cells that cover entire surface of plant is called Epidermis. It is made up of a single layer of cells. It protects all parts of the plants. Most of the epidermal cells are relatively flat. The outer wall and side walls are thicker than inner walls. In some plants living in very dry habitats, the epidermis may be thicker since protection against water loss is critical. On the aerial parts of the plants, epidermal cells often secretes a waxy, water resistant layer on their outer surface. It provides protection against loss of water, mechanical injury and invasion by microbes. As epidermal tissues protect the plants, the cells of epidermal tissues form a continuous layer and they have no intercellular spaces between them. Epidermal cells of leaf bear small pores known as stomata. These are enclosed by two kidney- shaped cells called guard cells. Epidermal cells of the roots have long hair-like outgrowth called root hairs. These increase surface area to absorp water from the soil. In desert plants, epidermis has thick waxy coating of cutin (waterproof quality) on its outer surface to prevent water loss. b) Cork- It is the secondary meristem, which replaces the epidermis of older stems. Cells of cork are dead, compactly arranged and have no intercellular spaces. It forms bark of the tree. A chemical called Suberin is present in their walls. It makes them impervious to gases and water. B. Complex Permanent Tissue- Complex permanent tissues are made up of more than one type of cells. All these cells cordinate to perform a common function. Complex tissues transport water, mineral salts and food material to various parts of plant body. Types of complex permanent tissues are: a) Xylem b) Phloem. Both xylem and phloem are conducting tissues and also known as vascular tissues and together called vascular bundles.  TISSUES 1. Xylem- It is also known as vascular/mechanical/conducting tissue. It is responsible for the transport of water and minerals from roots to other parts of the plant. The cells of xylem have thick walls and many of them are dead. Xylem consists of 4 types of cell called elements. – 1. Tracheids 2. Vessels / Tracheae 3. Xylem parenchyma 4. Xylem sclerenchyma / fibres 1. Tracheids- These are dead, long, tubular cells with tapering ends. These conduct water and minerals vertically. Since tracheids do not have open ends like the vessels, so water has to pass from cell to cell via the pits. 2. Vessels / Tracheae- These are also dead, tube-like cells formed by a row of cells, placed end to end. Vessels are shorter and wider than tracheids. The walls of Vessels are lignified. (cell wall that are thickend by lignin are called lignified cell wall) These also conduct water vertically. The transverse walls between the vessel eliments are partially or completely dissolved to form continuous channels or water-pipes. 3. Xylem parenchyma- These are only lliving cells of xylem with thin cell walls. These store food and helps in lateral conduction of water. 4. Xylem sclerenchyma / fibres- These are elongated dead cells with tapering ends and thick cell walls. These provide support to xylem tissue. ❖ Since walls of tracheids, vessels and sclerenchyma of xylem are lignified, they give mechanical strength to plant body. 2. Phloem- Like xylem, phloem contains tubes but performs no mechanical function. It transports foods from leaves to other parts of the plant. Materials can move in both directions in it. Phloem is made up of four elemnts or cells. – 1. Seive tubes 2. Companion cells 3. Phloem parenchyma 4. Phloem fibres Except phloem fibres, phloem cells are living cells  TISSUES 1. Seive tubes- These are tubular cells with thin cell wall. Walls of seive tube are perforated meaning the walls contain numerous pores called seive plates. The cells of seive tube have thin layer of cytoplasm. Nuclei are absent in mature seive tube cells. 2. Companion cells- These are associated with seive tubes. These are small elongated cells having thin cell walls. Walls of these cells are non perforated. These have dense and active cytoplasm and large elongated nucleus. These help seive tubes in translocation of food. 3. Phloem parenchyma- These are thin walled cells. these help in storage and slow lateral conduction of food. 4. Phloem fibres- These are thick walled sclerenchyma cells. These provide mechanical strength to the tissue.  TISSUES ANIMAL TISSUES On the basis of the functions, the animal tissues are classified as 1. Epithelial tissue 2. Muscular tissue 3. Connective tissue 4. Nervous tissue Epithelial tissue – The covering or protective tisues in the animal body are epithelial tissues. It is the simplest tissue. It covers most organs and cavities of the body. The cells of this tissue are tightly packed and they form a continuous sheet. These also forms a barrier to keep different body system separate from each other. The cells in the epithelial tissues have no intercellular space. The skin and inner lining of buccal cavity, blood vessels, alveoli and kidney tubules are made of epithelial tissue. Depending upon the shape and function of the cells, the epithellial tissues are classified as :- a) Squamous epithelium b) Cuboidal epithelium c) Columnar epithelium d) Glandular epithelium e) Ciliated epithelium FUNCTIONs- 1. The cells of e[ithelium protects the underlying cells from drying and injury. 2. These tissues also protect the body from viral or bacterial infection. 3. Epithelial tissues help in absorption of water and nutrients. 4. Epithelial tissues help in elimination of waste products. 5. Some epitheilial tissue secrete a variety of substances such as sweat, saliva, enzymes, etc.  TISSUES a) Squamous epithelium- Squamous epithelial tissue constitute the skin which protects the body. It further divided as – Simple squamous epithelium and Stratified squamous epithelium. 1. Simple squamous epithelium- It is made up of single layered thin, flat, irregular shaped cells which fit together like floor tiles to form a compact tissue. It forms delicate lining of blood vessels, nose, oesophagus, mouth, alveoli etc. It protects the underlying parts of body from mechanical injury, entry of gems, chemicals and drying. It also forms a selectively permeable surface through which filteration occurs. 2. Stratified squamous epithelium- It is found in the outer side of skin. This is water-proof and highly resistant to mechanical injury. Cells of stratified squamous epithelium are arranged in many layers to prevent their wear and tear. b) Cuboidal epithelium- It is made up of cube-shaped cells, which have round nuclei. It forms lining of kidney tubules and ducts of salivary glands, sweat glands and exocrine glands. It forms germinal epithelium of gonads (testes and ovaries). It helps in absorption, excretion and secretion. It also provides mechanical support. c) Columnar epithelium- It is made up of tall, pillar-like cells, with elongated nuclei. It forms the inner lining of intenstine, stomach, where absorption and secretion occur. It also forms linning of gall bladder and oviduct and facilitates movement across the cells. Its main function is absorption and secretion. d) Glandular epithelium- Sometimes, portion of epithelial tissue folds inward. This results in the formation of a multicellular gland. Its tissue is called Granduilar epithelium. These epithelium is often modified to form glands which secrete chemicals. Gland cells secrete chemicals at the epithelial surface. e) Ciliated Epithelium- When columnar epithelial cells possess cilia (hair-like projection) then it is called ciliated epithelium. Due to rhythmic beating of the cilia, it has the ability to move substances like mucus forward. It is found in the respiratory tract and also lines oviducts, sperm ducts, kidney tubules, etc. Muscular Tissue- Muscular tissues are consists of elongated cells also called muscle fibres. These tissues are responsible for the movement in our body.  TISSUES These tissues contain contractile protiens which causes movement of muscles by contraction and relaxation. The movements of the internal organs such as heart and alimentary canal, are all caused by muscle tissues. Muscle cells are arranged in parallel arrangement to work together effectively. Different types of muscular tissues are – 1. Striated muscles 2. Unstriated or smooth muscles 3. Cardiac muscles Striated muscles- These muscles are mostly attached to bones and in help in body movement, so these are also called skeletal muscle. These are also called voluntary muscles as we can move them on our own will. The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei). Under the microscope, these muscles show alternate light and dark bands or striation, so these are called striated muscles. Striated muscles occur in the muscles of limbs, face, neck, tongue, diaphragm etc. Unstriated or smooth muscle- The muscles which we cannot move as per our will are called unstriated or smooth muscles. And thsese are also called involuntary muscles. These muscles are present in alimentary canal, blood vessel, iris of eyes, uterus and bronchi of lungs. The cells of these muscle are long, with pointed ends (spindle shaped) and uninucliate (having single nucleus). These muscles do not show any dark or light band. So, these are also called unstriated muscles. Cardiac Muscle- These are involuntary muscles present only in heart. They perform rhyhtmic contraction and relaxation throughout the life. The cells of these muscle are cylindrical. Uninucleate and branched. Cardiac muscle shows charachteristics of both smooth and striated muscles. These have stripes of light and dark bands. Connective tissues- The connective tissue is specialised to connect various body organs with each other. This connects bones to each other, muscle to bones, bind tissues and can also give support to various parts of body. The cells of connective tissues are loosely packed, living, separated from each other and low in number. The connective tissues are mainly filled with gel-like intercellular substance called medium or matrix. The nature of matrix differs with the function of the particular connective tissue. There are different types of connective tissues, those are- blood, bone, ligaments, tendons, cartilage, areolar tissue, adipose tissue.  TISSUES Blood- I. It is a fluid connective tissue. II. It contains fluid matrix called plasma and blood cells such RBCs, WBCs and platelets. III. Plasma also contains proteins, salts and hormones. IV. Blood transports nutrients, gases, hormones and vitamins to various tissues of the body. V. It carries excretory products from tissues to excretory organs. VI. It also conduct heat and regulate body temperature. RBCs (Red Blood Cells)- It is also called erythrocytes. It helps in transport of oxygen and carbon dioxide with the help of haemoglobin. Due to the presence of haemoglobin RBC get its red pigment. The RBCs are circular, disc-like and lack of nuclei in mammals. The average life span of RBCs is 120 days. WBCs (White Blood Cells)- It is also called leucocytes. These fight with diseasesby producing antibodies. WBCs are of two types- Phagocytes and Immunocytes. Phagocytes carry out body defences by engulfing bacteria and other foreign substances. Immunocytes produces antibodies and are involved in the immune response. Blood Plateletes- It is also called thrombocytes. These help in the clotting of the blood. Bone- I. It is a very strong non-flexible tissue. II. It is porous, highly vascular, mineralised, hard and rigid. III. Its matrix is made up of proteins and rich in salts of calcium and phosphorous. IV. It forms the framework that support the body. V. It protects and supports the vitals organs such as brains, lungs, etc. VI. It also anchors the muscle. Ligaments- I. These are elastic and has great strength and connect one bone to other bone. II. It contains very little matrix. III. A ligament is made up of white as well as yellow fibres. IV. Ligaments strengthen the joints and permit normal movements. V. Overstrecthing of ligaments leads to sprain. Tendons- I. These are strong, inelastic structures that join skeletal muscle to bones. II. A tendon is made up of white fibrous tissues with limited flexibility but has a great strength. Cartilage- I. It is a specialised connective tissue having widely spaced cells.  TISSUES II. It has solid matrix called chondrin which is composed of proteins and sugars. III. Cartilage provides smoothness to the bone surfaces at the joints. IV. Cartilage also provide support and flexibility to the body parts. V. It present in nose, ear, trachea and larynx etc. ❖ (We can fold the cartilage of the ear but we cannot bend the on our arms.) Areolar tissue- I. It is a supporting and packing tissue between organs lying in the body cavity. II. It is a loose and cellular tissue. It fills the space inside the organs, supports internal organs. III. It is located between skin and muscles, around blood vessels and nerves and in the bone marrow. IV. It helps in repair of tissues after an injury. Adipose tissue- I. It acts as a store house of fats. Fat cell is rounded or oval in shape and contains a large droplet of fat. II. Adipose tissue is acts as an insulator due to the storage of fats. III. It keeps visceral organs in position. It forms shock-absorbing cushions around kidnwy and ey balls. IV. It is located below the skin in between internal organ. NERVOUS TISSUE- The tissue that receive stimulus and transmit it from one part of the tissue to other, are nervous tissue. Brain, spinal chord and nerves are all composed of nervous tissue. The cells of the nervous tissue are called neurons or nerve cells. Each neuron may be upto a metre long and has three major parts- o Cell body or Cyton- it consists of cytoplasm and nucleus and cell membrane. o Axon- it is a single, long conducting fibre extending from neuron. It transmits impulse away from the cell body. o Dendrites- these are short branched fibres of neuron. These receives nerve impulse. Many nerve fibres bound together by connective tissue make up a nerve. Nerve impulse allows us to move our muscle according to our will.