Tissues
- Multicellular organisms consist of many groups of specialised cells making up their tissues and organs.
- Differentiation is the process by which unspecialised structures become modified and specialised for performing specific functions.
- Differentiation results in division of labour.
- The study of the structure of tissues and organs is known as histology.
- Based on ability to divide, plant tissues may be classified as meristematic tissue and permanent tissue.
- Meristematic tissues are responsible for growth in plants.
- The part of the plant body where meristematic tissues are present is called meristem.
- Meristematic cells possess the power of cell division.
- Permanent tissues are those which have lost the capacity to divide.
- 1 Based on function, permanent tissues are classified as protective tissues, supporting tissues, conducting tissues and secretory tissues.
- Parenchyma is a widely distributed, simple plant tissue.
- Collenchyma is a strong and flexible mechanical tissue.
- Like collenchyma, sclerenchyma is also a strengthening and protective tissue.
- Xylem and phloem are the conducting tissues or vascular tissues/ also called complex tissues.
- Xylem is popularly known as wood.
- Xylem is composed of tracheids, vessels, xylem parenchyma and xylem fibres.
- In higher plants, xylem and phloem usually occur together forming vascular bundle.
- Phloem is composed of sieve tubes; companion cells, phloem parenchyma and phloem fibres.
- Protective tissues include epidermis and cork.
- In old roots and stem, the epidermal tissue at the periphery is replaced by cork.
- Four basic types of animal tissues are - epithelium or epithelial tissue, connective tissue, muscular tissue and nervous tissue.
- The epithelial cells lie close together with little or no intercellular substances.
- The main function of epithelium is to give protection to the underlying tissues.
- Connective tissue serves to 'connect' or 'bind' the cells of other tissues in the body and gives them rigidity and support.
- Areolar connective tissue is of two types - white fibres (made of collagen) and yellow fibres (made of elastin).Tendon is made up of white fibres and connects muscles to bones.
- Ligaments consist of yellow fibres and connect one bone to another bone.
- Cartilage is a non-porous connective tissue.
- Bone is very strong, rigid and porous tissue.
- Bone is surrounded by a connective tissue known as periosteum,
- Bones make up approximately 15% of body mass of an adult.
- Blood is a bright, red-coloured fluid connective tissue consisting of plasma and blood cells (erythrocytes, leucocytes and platelets).
- Muscular tissue is a contractile tissue which possesses myofibrils, sarcoplasm, sarcolemma, etc.
- The main function of muscular tissue is to bring about movement of body parts and locomotion of individual.
- Muscular tissue is of three types - striated or voluntary, smooth or involuntary and cardiac muscles.
- Nervous tissue is a very specialised tissue for receiving stimuli or sensations and transmitting messages.
- Nerve cells or neurons form the most important elements of nervous tissue.
The three main parts of a neuron are cell body or cyton, Dendron and the axon.
