Biology IX | Tissues, Organs, Organ System, Organism | Part 2

Tissues, Organs, Organ System, Organism | Part 2


Cell are organized into four types of tissues in higher animals including man

(i) Epithelial tissue : –

It is a protective covering tissue and forms a continuous layer on the entire body surface and cavities inside the body and its parts.

The skin, surface layers of mouth, alimentary canal and lungs are made of epithelial tissues.

It helps in the exchange of materials between the body and the external environment and between different part of body.

Depending upon the shape and function of the cells, the epithelial tissues are classified as.

(a) Squamous epithelium

(b) Cuboidal epithelium

(c) Columnar epithelium

(d) Glandular epithelium

(a) Squamous epithelium : –

These are thin, flat, form a delicate lining the oesophagus and the lining of the mouth are also covered with squamous epithelium.

The skin, is also made of squamous epithelium, these skin cells are arranged in many layers to prevent wear and tear of the body.

Those epithelium which are arranged in a pattern of layers are called stratified squamous epithelium.

(b) Cuboidal epithelium (with cube shaped cells) : –

These forms the lining of the kidney tubules and ducts of salivary glands.

Epithelial cells often acquires additional specialization as gland cell, which can secrete substances at the epithelial surface.

(C) Columnar (Ciliated) epithelium : –

In the inner lining of the intestine, secretion and absorption is occurs through it.

In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair like projection on the outer surfaces of epithelial cells, they can move and their movement pushes the mucus forward to clear it. This type of epithelium is thus called ciliated columnar epithelium.

(d) Glandular epithelium : –

Some times a portion of the epithelial tissue folds inward, and a multicellular gland is formed. Thus they are called is glandular epithelium.

Connective tissue

It performs the functions of binding, supporting and packing other different organs of the body.

Functions of connective tissues

Connective tissue binds different structures with one another e.g. muscles with skin muscles with bones.

Adipose connective tissue helps in storage of fats. It also forms shock proof cushions around kidneys ovaries and eye balls.

These forms a supporting frame work of cartilage and bones in the body.

Vascular connective tissue helps in transpiration of materials such as gases, food, wastes, hormones etc inside the body.

These form a protective sheaths around delicate organs such as kidneys testes etc.

Haemopoietic tissues of bone marrow helps in the formation of blood cells.

White blood corpuscles of blood and lymph act as phagocytes and they provide protection against bacterial infections.

Collagen fibers of connective tissue help in the repair of injured tissue.

The major connective tissues of the human body are

(a) Areloar connective tissue

(b) Tendons and ligaments

(c) Cartilage and bone

(d) Blood and Lymph.

Areolar connective tissue

Three types of cells are present in the matrix of the areolar tissue.

(i) Fibroblasts: These cells secrete yellow and white fibres.

(ii) Histocytes: These are phagocytic in nature and they engulf bacteria and other microbes

(iii) Mast cells: These cells secrete matrix.

Functions of Areolar tissue

Areolar connective tissue binds the skin with muscles, attaches blood vessels and nerves to the surrounding tissues.

It forms dermis of the skin.

It serves as packing material for almost all organs


The tendons in the matrix bundles of white fibres run parallel to one another. Tendons are tough and inelastic and they connect muscles with bones.


It contain matrix with numerous and closely packed yellow or elastic fibres, made up of elastin proteins. They are elastic and connect one bone with the other.


Cartilage consists of matrix impregnated with chondrin cartilage is bounded externally by white fibrous connective tissue called certichondrium.

In human beings, cartilage is present in the larynx, trachea, at the end of the bones nasal septum, and in between ribs and sternum.


The bone cells are called osteocytes. These are star shaped and each cell is enclosed in a small cavity called the lacuna. Lacunae are given out into conaliculi in which processes of osteocytes are present.

In mammalian bone the osteolytes are present in concentric rings around the central canal called the Haversian canal.

The Concentric rings of bone cells along with the Haversian canal is called Haversian system

The bones are bounded externally by a connective tissue called periosteum .


Blood consists of plasma and blood Corpuscles. Plasma is a straw-coloured fluid which contains 85-90% water and 5-10% of the organic and inorganic substances of sulphates.

Blood cell are of three types-

(i) Red blood cells (RBC) or Erythrocytes.

(ii) White blood cells (WBC) or Leucocyles.

(iii) Blood platelets.


It is a transparent yellow flied. It is chemically similar to blood plasma except that it contains very little proteins and it does not contain. R.B.C.

Due the absence of R.B.C. its colour is not red but it contain the another type of cells called W.B.C.

Lymph is present in the inter cellular spaces hence it is also called tissue fluid.

Muscles tissue

Muscles of the body are made of muscles cells or muscles fibres.

The movement of the body or limbs is brought about by contraction and relaxation of contractile proteins present in muscle cell.

The movement of the heart and alimentary canal are all caused by muscle tissue

There are three types of muscle fibres:-

(i) Striated muscle (skeletal muscle or voluntary muscle).

The skeletal muscles are attached to the bones and help in movement.

Cells of this tissue are long cylindrical, non tapering and Unbranched.

There are many nuclei (multinucleated) which are situated towards the periphery of the muscle fibre.

(ii) Unstriated muscle (Smooth muscle or involuntary muscle)

The smooth muscle tissues are found within the walls of all the tubular organs such as stomach, intertine, ureter, bronchi etc

The cells are long with pointed ends (spindle shaped)

The cell has only one nucleus (uninucleate) situated in the centre.

It does not show any stripes or striations across the muscle.

(iii) Cardiac muscle: –

This type of muscle tissue is exclusively present in the heart.

Composed of non-tapering cells with faint cross striations

Each cell contains one or two nuclei situated at the centre.

The function is rhythmic contraction and relaxation throughout life with out fatigue under normal condition.

The cells one cylindrical and branched.

Nervous tissue

Nerve cell or neurons are the structural and functional unit of nervous tissue.

In cytoplasm, Nissle’s granules are made up of neurofibrils and RNA. Cell organelles like mitochondria golgi-bodies etc are also present in the cytoplasm of nerve cell.

The axon is covered from outside by three layers- the innermost layer is called axulemna, the middle layer is called myselin sheath, or modularly sheath and outer most layer is called neurilemma.

The axolemma and neurilemma are continuous sheath, they are constricted at intervals. These constrictions are known as Nodes of Ranvier

The Loose connection between the axon endings of one nerve cells and the cyton of the next nerve cell is called Synapses

The small branches given out by cyton are called dendrons, which farther divide to form dendrites.

In dendrons and dendrites, Eytoplasm and Nissl’s granules are present.


Biology IX | Tissues, Organs, Organ System, Organism | Part 1

Tissues, Organs, Organ System, Organism | Part 1


Tissue can be defined as a group of cells more or less alike in size, shape, performing the same function and having common origin.

Histology :- The microscopic study of tissues and their functions is known as histology.


Plants body are made up of different kinds of tissues these are classified into two groups are

(I) Meristematic tissues

These are present only at the growing regions like shoot tip, root tip and Cambium (region which is responsible for growth in thickness)

These cells divide continuously thus helping in increasing the length and the growth of the plant.

Characteristics of meristematic tissue

(1) They are living cell; compactly arranged without intercellular spaces.

(2) They are thin walled are may be round oval, polygonal or rectangular. in shape.

(3) The vacuoles are few and smaller in size.

(4) They have dense granular cytoplasm.

(5) The nucleus is large and conspicuous.

(6) The cells are immature and undifferentiated.

(7) The plastids are in preplastid stage.

(8) They are capable of dividing indefinitely.

(9) They don’t store reserve food material.

(10) They are Usually found in the apices of root and shoot.

Type of meristems

According to their position in the plant body, meristems are divided into three Categories:-

(1) Apical meristem:- It is present at the growing tips of the stems and roots and increases the length of the stem and the root.

(2) Lateral meristem (Labium): The girth of the stem or root increases due to this meristem.

(3) Intercalary maristem :- It is present at the base of the leaves or internodes

(II)Permanent Tissues

Permanent tissues are derived from meristematic tissues till they lose the ability to divide.

They have the definite shape, and size

They may be living or dead, and thin or thick walled.

The cells are large having vacuolated cytoplasm.

Simple permanent tissues

The common simple permanent tissues are-

(a) Parenchyma

(b) Collenchyma

(c) Scleren Chyma

Parenchyma :- (Living)

It is widely distributed in plants body like stem roots, leaves, flowers and fruits.

The parenchymatous cell are isodiametric

They may be oval, round, polygonal, or elongated and have thin walls.

Functions of Parenchymatous tissue

It store and assimilate food.

It provide mechanical strength.

It Stores waste products such as tannin, gum, crystals, resins of inorganic waste etc.

(b) Collenchyma (Living)

These cell are present below the epidermis

It consist of thin walled cells, which are much thickened at the corners where number of cells joint together. The thickening is due to a deposition of cellulose and pectin at the corners.

Intercellular spaces are absent

It may be circular, oval or polygonal

Main Functions of collenchyma

They provides the mechanical support and elasticity to the plants.

They manufacture sugar and starch when they contain chloroplasts.

(C) Sclernchyma

The cell of this type of tissue are long, narrow, thick and lignified.

The length of the sclerenchyma cells varies. From 1 mm to 550 mm in different plants.

It also provides mechanical support to the plants.

Some times specials types of sclerenchyma cell called “Sclereids” develop in various parts of the plant, such as cortex, pith, phloem & hard seeds –etc.

(ii) Protective Tissue

These tissue are usually present in the outermost layer of the plant body such as leaves, flowers, stem and roots.

This layer is one cell thick and is covered with cutin, and protect the inner tissues present in the plant body.

The walls of these cells are heavily thickened by the deposition of suberin which help in prevention of loss of water.

It is used for insulation, shock absorbers, linoleum and sport good.

This layer contain the small opening called pores or stomata which helps in transpiration and exchange of gases.

(iii)Complex permanent tissues

Complex tissues are made up of more than one type of cells and work together as a unit

Complex tissues are to two types-

(a) Xylem

(b) Phloem

(a) Xylem:-

This conducting tissue is composed of cells. i.e., elements of four different Kinds-tracheids, Vessels or tracheas, Xylem parenchyma and xylem sclerenchyma

These carry water and mineral salts upward from the root to different parts of the shoot.

(b) Phloem

It is composed of tour elements are sieve tubes companion cells, phloem parenchyma and phloem fibres.

In this tissue, sieve tubes have perforated walls, which helps in translocation (distribution of the prepared food).