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Representative Sample Biology: Tissues TISSUES 1. Introduction Organisms are either unicellular or multicellular. Accordingly the functions are performed either by a single cell or by a group of cells. Cells, tissues, organs and organ systems split up the work in a way that exhibits division of labor and contribute to the survival of the body as a whole. This work division ensures proper specific defined function of the body. In Unicellular organisms like bacteria, all the functions like digestion, respiration and reproduction are performed by a single cell. In the complex body of multicellular animals, the same basic functions are carried out by groups of cells in a well-organized manner. The body of a simple organism like Hydra is composed of different types and the number of cells. The human body is composed of billions of cells to perform various functions. In multicellular animals, a group of similar cells along with intercellular substances perform a specific function. Such an organization is called as tissue. Tissues vary according to their origin and function, and are different in plants and animals. 2. Types of Tissue in A Plant Plant tissues can also be divided differently into two types on basis of their division ability: 1. Meristematic tissues 2. Permanent tissues. 2.1. Meristematic Tissue Meristematic tissue consists of actively dividing cells, leading to increase in length and thickness of the plant. The primary growth of a plant occurs only in certain, specific regions, such as in the tips of stems or roots. It is in these regions that meristematic tissue is present. Meristematic tissues are classified on the basis of their location. They are of the following types: (a) Apical Meristem: Apical meristem is present on the stem apex, root apex, flower buds and leaf buds. They are actively dividing cells that require proper nutrition and energy for the division and Tissues 44 hence are green in color to carry out photosynthesis. They are responsible for growth in length, i.e. primary growth. (b) Lateral Meristem: Lateral meristems are found along the side of the stem. It consists of cells which mainly divide in one plane and cause the organ to increase in diameter and growth. Lateral Meristem usually occurs beneath the bark of a tree in the form of Cork Cambium and in vascular bundles of dicots in the form of vascular cambium. They are responsible for growth in girth or width, i.e. secondary growth. (c) Intercalary Meristem: Intercalary meristem is present at the base of a leaf or internodes. They are present on the either sides of the node. Fig: Position of meristem in a growing plant PLANCESS CONCEPTS The cells of meristematic tissues are similar in structure and have thin and elastic primary cell wall made up of cellulose. Each cell contains a dense cytoplasm and a prominent nucleus. Normally the meristematic cells are oval, polygonal or rectangular in shape. Meristematic tissue cells have a large nucleus with small or no vacuoles; they have no intercellular spaces. Vipul Singh AIR 1, NSTSE 2009 www.plancessjee.com 45 Tissues Mind Map: 2.2. Permanent Tissue When the cells of a meristematic tissue divide to a certain extent, they become specialized for a particular function. This process is called as the differentiation. After differentiation, the cells lose their capability to divide and is differentiated to their capability to perform various functions of the organism. The tissue becomes permanent tissue after differentiation. Permanent tissues are of two types, the simple permanent tissue and the complex permanent tissue. (a) Simple permanent tissue: These tissues are called simple because they are composed of similar types of cells which have common origin and function. Simple permanent tissues are of three types, viz. parenchyma, collenchyma and sclerenchyma. 1) Parenchyma: The cells of parenchyma have thin cell wall. They are loosely packed; with a lot of intercellular spaces between them. Parenchyma consists of the largest portion of a plant body. The main function of parenchyma is to provide support and to store food. In aquatic plants, large air cavities are present in parenchyma. Some parenchyma contain chlorophyll and perform photosynthesis, in this case it is called a chlorenchyma. Parenchyma with large air cavities provide buoyancy to the plant, then the parenchyma is known as aerenchyma. 2) Collenchyma: Collenchymatous tissue acts as a supporting tissue in the stems of young plants. It provides mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing sugar and storing it as starch. It is present in the margin of leaves and resists tearing effect of the wind. Cells are elongated with thick primary walls thickened with cellulose and no intercellular spaces. Cells that have chloroplasts perform photosynthesis. Tissues 46 3) Sclerenchyma: The cell wall is very thick with lignin which is a water proof material. The cells are dead and intercellular space is absent. The nucleus is absent. It provides a structural rigidity to the plant parts. Examples of sclerenchyma are bark, coconut husk. They are fibers present in a vascular tissue to transport water or sclereids found in the cortex, pith, phloem for strength and firmness. These cells are involved in a mechanical support and protection for seeds. PLANCESS CONCEPTS The cells of sclerenchymatous cells can be classified as: Fibers- Fibers are long, elongated sclerenchymatous cells with pointed ends. They help in water transportation. Sclerides- These are sclerenchymatous cells which are short and possess extremely thick, lamellated, lignified walls with long singular piths. The main function of Sclerenchymatous tissues is to give support to the plant. Vipul Singh AIR 1, NSTSE 2009 Mind Map: b) Complex permanent tissue: The complex tissue consists of more than one type of cells which work together as a unit. Complex tissues help in the transportation of organic material, water and mineral up and down the plants. That is why it is also known as conducting and vascular tissue. Complex permanent tissues are of two types, viz. xylem and phloem. Xylem and phloem together make the vascular bundle in plants. www.plancessjee.com 47 Tissues i) Xylem: Xylem consists of: • Tracheid • Vessel Members • Xylem fibers • Xylem parenchyma. Xylem is a chief, conducting tissue of the vascular plants. It conducts water and mineral ions. The cells of xylem are dead; except the cells of xylem parenchyma. Tracheid and vessels are tubular structures and thus they provide a channel for conduction of the water and minerals. Xylem fiber provides structural support to the tissue. Xylem parenchyma stores the food. Fig: Position of Xylem in plant Tissues 48 Fig: Structure of tracheid, sieve-tube, sieve-plate, vessel membranes of Xylem. ii) Phloem: Phloem consists of: • Sieve tube • Sieve cell • Companion cell • Phloem fibre • Phloem parenchyma. Sieve tubes are tubular cells with perforated walls. Sieve tubes are the conducting elements of phloem. Phloem is responsible for the translocation of food in the plants. The transport of food in phloem is both upward and downward movement. www.plancessjee.com 49 Tissues Mind Map: PLANCESS CONCEPTS Plant tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, and the vascular tissue. • Epidermis - Cells forming the outer surface of the leaves and of the young plant body. • Vascular tissue - The primary components of a vascular tissue are the xylem and phloem. These transport fluid and nutrients internally. • Ground tissue - Ground tissue is less differentiated than other tissues. Ground tissue manufactures nutrients by photosynthesis and stores reserve nutrients. Vipul Singh AIR 1, NSTSE 2009 Tissues 50 3. Types of tissue in animal Animal tissues are of four types, viz. epithelial tissue, connective tissue, muscular tissue and nervous tissue. 3.1. Epithelial Tissue The epithelial tissue forms a covering or lining of most of the organs. The cells of epithelial tissue are tightly packed and form a continuous sheet. There is a small amount of cementing materials between the cells and there is no intercellular space. Due to the absence of blood vessel supply to the epithelium, its permeability plays an important role in the exchange of materials among various organs. It also plays an important role in osmoregulation. All epithelial tissues are separated by the underlying tissue by an extracellular fibrous basement membrane. Epithelial tissues are of the following types: a) Simple Epithelium: The simple epithelium is composed of a single layer of cells. This type of epithelial tissue forms the lining of blood vessels and alveoli facilitating exchange of gases and fluids. b) Cuboidal Epithelium: These cells are cube-shaped, provide a mechanical support. Linings of kidney tubules and ducts of salivary glands are composed of cuboidal epithelium. Cells of epithelium may play the role of secretion and then they are called glandular epithelium. It helps in secretion, excretion and absorption of materials from the food or blood. c) Columnar Epithelium: These cells are columnshaped that facilitates secretion and absorption. Example: the lining of the intestine is composed of columnar epithelium. In some organs, columnar epithelium has cilia present on the outer surface which facilitate movements of certain substances. www.plancessjee.com 51 Tissues The ciliated epithelium in the respiratory tract pushes the mucus forward produced in the goblet cells. d) Stratified Epithelium: Cells of the stratified epithelium are in many layers. Basal layer is in contact with the basement membrane and newer cells occupy the upper layers. Skin is an example of stratified epithelium. Stratification of layers prevents wear and tear. This is highly water proof and resistant to mechanical injury. Mind Map: 3.2. Connective Tissue The cells of a connective tissue are loosely scattered in a matrix secreted by its cells. The matrix can be a fluid, jelly like, dense or rigid. The nature of the matrix depends on the function, which a connective tissue serves. It helps in binding bones and cartilages, packing, supporting structures of the body. Following are the various connective tissues: i) Connective tissue proper: matrix – jelly, less rigid. ii) Skeletal Tissue: matrix is solid. iii) Vascular tissue: matrix is fluid. i) Connective tissue proper: Loose Connective tissue proper: It has less fiber and more matrix. Dense Connective tissue proper: It has more fiber and less matrix. Tissues 52 Loose Connective tissue proper: a) Areolar Connective Tissue: Areolar tissue is found between the skin and muscles, around the blood vessels and nerves and in the bone marrow. Areolar tissue fills up the gap between the tissues and provides support. It also helps in repairing the tissues, as packing material, produces antibodies. b) Adipose Tissue: Adipose tissue is composed of fat globules. This tissue is found below the skin and beneath the organs. Adipose tissue provides an insulation and works as a cushion. Adipocytes are large cells with soft jelly like matrix and less fibers. Dense Connective tissue proper: a) Tendon: It is a tough non fibrous dense tissue. It is white in colour with great strength and less flexibility. It joins skeletal muscle to the bone for contraction. b) Ligament: It is a dense yellow fibrous tissue with strength and elasticity that binds bones together for bending. ii) Skeletal Tissue: a) Bone: The bone is mainly composed of osteoblasts. The bone makes the skeletal system. The skeletal system is responsible for providing a structural framework to the body. It provides protection to important organs and facilitates movements. It has a fluid in it that is called as the bone marrow. The matrix is concentric rings made up of collagenous protein. b) Cartilage: The cartilage is mainly composed of chondrioblasts. The cartilage is present at the ends of the articulatory bones. Cartilage is also present in external ear, bronchii, etc. a nonporous tissue filled with a fluid called lacunae. The major function of the cartilage is support and flexibility. iii) Vascular tissue a) Blood: The blood is composed of blood cells, platelets and plasma. The blood plays an important role in the transportation of various substances in the body. It also helps in osmoregulation and temperature control, transportation of oxygen and nutrients. b) Lymph: It is a light yellow colored fluid made up of plasma and WBC. It helps in exchange of materials between blood and tissue fluid. (contd.) www.plancessjee.com 53 Tissues Exercise — 1 Fill in the Blanks Q.1. meristem occur at the apices of the roots and stem. Q.2 type of parenchyma is seen in Petiole of banana. Q.3 When Xylem and Phloem are arranged on alternate radius then the Vascular Bundle of type. Q.4 Radial Vascular Bundle is seen in Q.5 Meristem producing the secondary xylem and phloem is called . Q.6 Hard lignified thick walled, long and pointed cells in a plant are . Q.7 Collenchymatous hypodermis is found in . Q.8 Transpiration and exchange of gases are the functions of Q.9 Parenchyma: Simple::Phloem: Q.10 Striated muscle is also called . . . True/False Q.11 Most of the plant tissues are supportive type. True False Q.12 Tissue ensures division of labor. True False Q.13 Sedentary existence contributes to the organ system design in animals. True False Q.14 Organ system is more complex in animals than in plants. True False Q.15 Cartilage heals slower than the skin because cartilage is a deeper tissue. True False Q.16 The inside lining of the intestine has a large surface area because of the presence of cilia. True False Q.17 Adipose is a type of connective tissue because that is where fat is stored. True False (contd.) Tissues 54 Exercise — 2 Multiple Choice Question: Q.1 Histamine secreting cells are found in: a) Connective tissue b) lung c) muscular tissue d) nervous tissue Q.2 The layer of skin that actively divides is: a) Stratum compactum b) Stratum corneum c) Stratum lucidum d) Stratum malphigi/stratum germinativum Q.3 Characteristics of simple epithelium is that they: a) Are arranged indiscriminately b) Continue to divide and help in organ function c) Make a definite layer d) None of the above Q.4 Collagen is a) Lipidb) Fibrous protein c) Globular proteind) Carbohydrate Q.5 Areolar connective tissue joins a) Haemoglobinb) Hirudin c) Myoglobind) Histamine Q.6 Hair present on the skin are: a) Epidermal in origin and are made of dead cells b) Epidermal in origin and are made of living cells c) dermal in origin and are made of living cells d) dermal in origin and are made of dead cells Q.7 The basement membrane is made up of: a) no cell product of epithelium b) epidermal cell only c) endodermal cell d) both a and c (contd.) www.plancessjee.com Tissues 55 SOLUTIONS EXERCISE 1 Fill in the Blanks: 1. apical meristem 2. Aerenchyma 3. radial 5. vascular cambium 6. Sclerenchyma 7. Dicot stems 9. Complex 10. Skeletal muscles 4. Roots 8. Stomata True/False: 11. True 12. True 13. False 14. True 17. False 18. True 19. True 20. False 15. False 16. False Match the Following: 21. 1 → e ; 2 → d ; 3 → a ; 4 → c ; 5 → b 22. 1 → c ; 2 → e ; 3 → d ; 4 → b ; 5 → a Very Short Answer Questions: 23. Ligaments24. Tendons 25. Cardiac muscle 26. Neuron 27. Bone marrow 28. Blood, lymph 29. Protein, salts, hormones 30. Study of blood. 31. Study of tissues. 32. Protection and mechanical support. 33. Apical meristem 34. Schlerenchymatous tissue Short Answer Questions: 35. The plant supporting tissues are the collenchyma and the sclerenchyma. The collenchyma is made up of living and elongated cells that accumulate cellulose and pectin in some regions of the cell wall making them unequally thick and thus providing flexibility. (contd.) Tissues 56 SOLUTIONS EXERCISE 2 Multiple Choice Question: 1. A 2. D 3. C 4. B 5. D 6. A 7. A 8. A 9. D 10. B 11. B 12. C 13. A 14. B 15. B 16. C 17. D 18. A 19. A 20. C 21. D 22. C 23. B 24. D 29. A 30. A Assertion & reasoning: 25. A 26. C 27. A 28. C 31. B 32. C 33. A 34. B 36. B 37. E 38. C Picture based: 35. C (contd.) www.plancessjee.com