(1) A tissue is a group of cells that are similar in structure and work together to perform a particular function.
(2) Plant Tissue
(i) Meristematic tissues are dividing tissue located at certain specific regions necessary for growth of plants.
Classification of the meristematic tissue is depend on the region where they are present-
(a) The meristem which is present at the growing tips of stems and roots and increases the length of the stem and root is called apical meristem.
(b) The meristem responsible for the girth of the stem or root increase is called lateral meristem (cambium).
(c) The meristem which is located near node is called intercalary meristem.
Characteristics of the meristematic tissues –
(a) Cells are very active.
(b) They have dense cytoplasm.
(c) They have thin cellulose walls.
(d) Nucleus is prominent.
(e) They lack vacuoles.
(ii) The tissues which are formed from meristematic tissues, have non dividing cells, give permanent shape and size to plant is called permanent tissues.
The process in which tissues cells are taking up permanent shape, size is called differentiation. Differentiation leads to the development of various types of permanent tissues.
Types of permanent tissues
(a) A few layers of cells beneath the epidermis are generally called simple permanent tissue.
Types of simple permanent tissue –
(A) The most common simple permanent tissue, which lives within the cell wall, large intercellular spaces and store food is known as parenchyma.
Types of parenchyma tissues-
(A.1) When chlorophyll of parenchyma tissues performs photosynthesis, parenchyma tissues are called chlorenchyma.
(A.2) The parenchyma tissues of aquatic plants which have large air cavities to help them float are called aerenchyma tissues.
(B) The permanent tissues which provide flexibility and mechanical support in plants, find in leaf stalks below the epidermis are called collenchyma.
The collenchyma tissues cells are living, elongated, irregularly thickened at the corners and have very little intercellular space.
(C) The permanent tissues which makes plant hard and stiff, present in stems around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts are known as sclerenchyma.
The sclerenchyma tissues cells are dead, long and narrow as the walls are thickened due to lignin because of no intercellular space.
The outermost layer of cells which is made up of a single layer of cells form a continuous layer without intercellular spaces is called epidermis.
Role of the epidermis in different parts of the plants and in dry habitat
Epidermis in dry habitat-
In dry habitats, the epidermis may be thicker to protect water loss. Epidermis cells on the aerial parts of the plant often secrete a waxy, water resistant layer of cutin (chemical substance with water proof quality)on their outer surface . These cells also protect plant from mechanical injury and invasion by parasite fugi.
Epidermis cells of the leaf-
The small pores in the epidermis of the leaf are called stomata.
The stomata which are enclosed by two – shaped cells are called guard cells.
Use of the stomata-
(A) Necessary for exchanging gases with the atmosphere.
(B) Transpiration (loss of water in the form of water vapour) also takes place through stomata.
Epidermis cell of the root –
The function of the epidermis cell of the root is to absorb water which increases by the long hair like parts of the roots.
Changes in the cells of older plants –
A strip of secondary meristem located in the cortex forms layers of cells which constitute the cork of dead cells with no intercellular spaces.
(b) Complex permanent tissue –
The permanent tissues which are made of more than one type of cells to perform a common function are called complex permanent tissues.
Eg:- Xylem and phloem.
Xylem and phloem both are conducting tissues and constitute a vascular bundle which are necessary for the survival of the plants in terrestrial environment.
(A) They consist of tracheids, vessels, xylem parenchyma and xylem fibres.
(B)Tracheids and vessels have thick walls and many are dead cells when mature.
(C) Tracheids and vessels are tubular structures which allow them to transport water and minerals vertically.
(D) Xylem fibres are mainly supportive in function.
(A) It is made of five types of cells which are sieve cells, sieve tubes, companion cells, phloem fibres and the phloem parenchyma.
(B) Sieve tubes are tubular cells with perforated walls.
(C) Phloem transports food from leaves to other part of the plant.
(D) Except phloem fibres, other phloem cells are living cells.
(2) Animal Tissues-
(i) Epithelial Tissue
The tissues which cover most organs and cavities within body and form a barrier to keep different body systems separate are called epithelial tissues. In simple words, covering and protective tissues in the animal body are epithelial tissues.
Eg:- The skin, lining of the mouth, the lining of the blood vessels, lung alveoli and kidney tubules
Epithelial tissues cells are tightly packed and form a continuous sheet with small amount of cementing material and no intercellular spaces.
The permeability of the cells of various epithelia plays an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body.
Types of the epithelial tissues on the basis of their functions-
(a) Epithelial tissues cells which are extremely thin and flat and form a delicate lining which prevent wear and tear are called simple squamous epithelium.
Eg:- The oesophagus and the lining of the mouth and the skin which protect our body.
Skin epithelial cells are arranged in layers, the epithelium is called stratified squamous epithelium.
(b) The epithelial tissues which absorb and secrete in lining of intestines and facilitate movement across the epithelial barrier are called columnar epithelial tissues.
Columnar epithelial cells are tall epithelial cells.
In the respiratory tract, these cells have cilia (hair like projections on the outer surfaces of epithelial cells) and their movement pushes the mucus forward to clear it. These epithelium cells are known as ciliated columnar epithelium.
(c) The epithelial tissues which are found in lining of kidney tubules and ducts of salivary glands where it provides mechanical support are known as cuboidal epithelial tissues.
Cuboidal epithelial cells are cube shaped epithelial cells.
(d) A portion of the epithelial tissues folds inward, and a multicellular gland is formed and is known as glandular epithelium.
(ii) Connective tissue – The epithelial tissues which are loosely spaced and embedded in an intercellular matrix which can be jelly like fluid, dense or rigid are called connective tissues.
(A) Blood has fluid matrix known as plasma in which red blood corpuscles, white blood corpuscles and platelets are suspended.
(B)The plasma contains proteins, salts and hormones.
(C) Blood flows and transports gases, digested food, hormones and waste materials to different parts of the body.
(A) Bone forms the frame work that supports the body and anchors the muscles.
(B) Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.
(C)Ligaments are elastic and very strong connective tissues which connect bones to bones.
(D)The connective tissues which are fibrous with great strength but less flexibility and connect bones with muscles are known as tendons.
(E)The connective tissues which have widely spaced cells, solid matrix are composed of protein and sugars, smoothens bone surfaces at joints is known as cartilage.
Types of connective tissues-
(a)The connective tissues which are found between the skin and muscles, around blood vessels and nerves and in the bone marrow are known as areolar connective tissue. It fills the space inside the organs, supports internal organs and helps in repair of tissues.
(b) The connective tissues that store fat found below the skin and between internal organs are known as fat storing adipose tissue.
The cell of fat storing adipose tissue cells are filled with fat globules. Storage of fats also lets it act as an insulator.
(iii) Muscular tissue-
The tissues which are responsible for movement in our body are called muscular tissue. The special protein that muscles contain and contract and relax to cause movement is called contractile proteins.
Muscular tissues cells are elongated cells (muscle fibre).
Type of muscular muscles-
(a) The muscles presents in animals move and stop according to their decision are called voluntary muscles.
Eg:- Muscles present in limbs move when we want to move and stop when we want to stop.
These muscles are also called skeletal muscles as they are attached to bones and help in movement. These muscles are also called striated muscles because under the microscope these muscles show light and dark band or striations when stained properly.
The cells of voluntary muscle tissue are long, cylindrical, unbranched and multinucleate.
(b) The muscles presents in animals move and stop not according to their decision are called involuntary muscles. The movements of these muscles can not be control by our body.
Eg:- (A) The movement of food in the alimentary canal
(B) The contraction and relaxation of blood vessels.
These muscles tissues are also known as unstrained muscles.
The unstrained muscles cells or involuntary muscles cells are long with pointed ends (Spindle – shaped) and uninucleate.
Eg:- Iris of eye, in ureters and in the bronchi of lungs.
The involuntary muscles of the heart show rhythmic contraction and relaxation throughout life are called cardiac muscles.
Heart muscle cells are cylindrical, branched and uninucleate.
(iv) Nervous Tissue –
The tissues which are highly specialized for being stimulated and than transmitting the stimulus very rapidly from one place to another in our body are called nervous tissues.
Eg:- Brain tissues, spinal cord tissues, nerves
The cells of nervous tissues are known as neurons or nerve cells. A neuron consists of a cell body with a nucleus and cytoplasm from which long thin hair –like parts arise which has a single long part axon and many branched parts dendrites. An individual nerve cell may be up to one metre long.
The signal that passes along the nerve fibre is called a nerve impulse which allows us to move our muscles when we want to.