- A tissue is a group of cells with a common origin, structure and function.
- The study of tissues is called histology.
The Plant Tissues –
The plant tissues are mainly of two types –
1. Meristematic (Gk. meristos : dividing)
2. Permanent (non-dividing)
- Meristematic Tissue –
(a) Apical Meristem
Location – Root tip and shoot tip.
Function – Growth in length of plants.(b) Inter-calary Meristem
Location – At the base of leaves or at the base of inter-nodes.
Function – Inter-nodal growth.(c) Lateral Meristem
Location – Cambium between xylem and phloem and cork. cambium in the cortex of dicot plants.
Function – Growth in thickness of the plant body. (secondary growth).
- Simple Tissues –
(a) Parenchyma –
Living; oval or round, thin walled with sufficient cytoplasm ; has prominent nucleus and intercellular spaces; wall made up of cellulose.
Pith and cortex of stem and root, mesophyll of leaves, endosperm of seed, xylem and phloem parenchyma in vascular tissue.
(i) They make large parts of various organs in most plants.
(ii) Act as storage cells. Turgid, parenchyma give rigidity to the plant body.
(iii) Chlorenchyma carries out photosynthesis.(b) Collenchyma –
Living; elongated cells with thick primary walls; thickenings more in the corners of the cells. Wall material is cellulose and pectin; intercellular spaces present.
Occur in the peripheral regions of stems and leaves.
Gives mechanical support to the plant body.(c) Sclerenchyma –
Dead; It consists of thick walled cells, walls uniformly thick with lignin. Fibres occur in patches or continuous bands in various parts of stem in many plants.
Sclereids occur commonly in fruit and seed.
Sclerenchyma is mainly a supporting tissue, which can withstand strains and protect the inner thin walled cells from damage.
- Complex tissues –
(a) Xylem –
It is a conducting tissue which conducts water and salts upward from roots to leaves.
It is composed of –
(iv) Xylem parenchyma(b) Phloem – Phloem too is a conducting tissue which conducts food synthesised in the leaves to different parts of the plant.
It is composed of –
(i) Sieve tubes
(ii) Companion cells
(iii) Phloem fibre
(iv) Phloem parenchyma
The Animal Tissues
(a) Epithelial Tissue –
The cells forming epithelial tissue are closely packed with no intercellular space in between. They are not supplied with blood vessels.If the epithelial cells are in a single layer, they form simple eptihelium. If the epithelial cells are arranged in many layers, they form compound epithelium or stratified epithelium (many layers). Stratified eptihelium is present in the body, where there is lot of wear and tear.
Example– skin, inner lining of cheeks etc.
line the surfaces, help in absorption, secrete, also bear protoplasmic projections such as the Cilia.
(b) Connecitve tissue –
The connective tissue has two components :
(i) matrix, the ground substance and
The matrix and cells are different in different connective tissues. Matrix is the ground substance.
Type of connective tissue
All the major topics are discussed separately.