These comprehensive RBSE Class 9 Science Notes Chapter 6 Tissues will give a brief overview of all the concepts.
RBSE Class 9 Science Chapter 6 Notes Tissues
→ A group of cells having similar structure and work together to achieve a particular function is called tissue.
→ Study of tissues is called Histology.
→ In unicellular organisms, single cell performs all basic functions, whereas in multicellular organisms (plants and animals) show division of labour as plant tissues and animals tissues.
→ Plant Tissues: Most of the tissues of plants are dead. They require less maintenance. There are some tissues in plants that grow throughout the life.
→ Animal Tissues : Most of the tissues of animals are living tissues as compared to dead tissues. They require more maintenance. Animals don’t show growth after reaching maturity.
→ Types of plant tissues : These are of two types – (i) Meristematic Tissues and (ii) Permanent Tissues
→ Meristematic Tissues : These tissues are having actively dividing cells and are found in actively growing parts. According to the position in plants, meristems are of three types – Apical, lateral and intercalary meristems. Cells of meristematic tissues are very active.
→ Permanent Tissues : These tissues are made up of meristematic tissues. Differentiation leads to form different types of permanent tissues. They are of two types – (i) Simple and (ii) Complex permanent tissues.
→ Simple Permanent Tissue : These are made up of one kind of cells which are similar in structure and function. These are divided as –
(i) Parenchyma : These tissue provide support to plants and also store food. It is a living and most common simple permanent tissue. It has thin cell wall. Cells are loosely packed, thus large intercellular spaces are found in this tissue. In some situations it contains chlorophyll and performs photosynthesis, then it is called chlorenchyma. In aquatic plants, large air cavities are present in parenchyma, then it is called aerenchyma.
(ii) Collenchyma : These tissues are flexible and provide mechanical support to plants. It is found below the epidermis of dicot stem and leaf stalk. Cell wall is irregularly thickened at corners. Cells are living, elongated with little intercellular space.
(iii) Sclerenchyma : It provides strength, hardness and stiffness to plants. Cells are dead, long, narrow and thickened with lignin. It is found in husk of coconut, coverings of seeds and around vascular bundles.
(iv) Guard cells and Epidermal tissue : Epidermal cells often secrete a waxy and water resistant layer on outer surface on the aerial parts of plant. It protects the cell against loss of water and mechanical injury. Stomata are present on the lower surface of leaf in epidermis. They are necessary for exchange of gases with atmosphere and guarded by two cells called guard cells. The epidermal form the several layer thick cork or the bark of the tree.
→ Complex Permanent Tissue : These are made of more than one type of cells. They are subdivided as Xylem and Pholem. These are also called conductive tissues.
(i) Xylem : It consists of (i) Tracheids, (ii) Vessels, (iii) Xylem parenchyma and (iv) Xylem fibres. It helps in conduction of water and minerals.
(ii) Phloem : It is composed of four type of cells – (i) Sieve tubes (ii) Companion cells (iii) Phloem parenchyma and (iv) Phoelm fibres. It transports food material to other parts of the plants. Phloem fibres are the only dead tissue among phloem elements.
→ Types of Animal Tissue : The following tissues are found in animals –
(i) Epithelial Tissue : It is a protective covering of animals forming a continuous sheet. These are classified in four types according to their shape and functions :
(a) Squamous Epithelium : The lining of mouth and oesophagus are covered .. with squamous epithelium. These are extremely thin and flat.
(b) Columnar Epithelium : These epithelial cells are present in the inner lining of the intenstine and columnar epithelium with cilia in the lining of respiratory tract.
(c) Cuboidal Epithelium : With cube shaped cells it forms the lining of kidney tubules and salivary glands.
(d) Stratified Squamous Epithelium : Skin epithelial cells are arranged in a pattern of layers, thus it is called stratified squamous epithelium.
(ii) Connective Tissue : Blood is a connective tissue. It consists of plasma, RBCs, WBCs and platelets. Bone is also a connective tissue. It forms the framework that supports the body and provides protection to vital organs like brain, heart and lungs etc. Cartilage is also a connective tissue.
(iii) Muscular Tissue : It is consist of elongated cells called muscle fibres. This tissue is responsible for the movement of our body. Muscular tissues are of three types :
(a) Striated or Voluntary Muscles
(b) Unstriated/smooth/involuntary Muscles
(c) Cardiac Muscles.
(iv) Nervous Tissue : It is made up of special type of cells called neuron or nerve cells. It performs the function of control and coordination in body.