Month: May 2022

class 11, epithilial tissue part – 2

It is formed of a single layer of cells, resting on the basement membrane. Simple epithelium occurs mainly on secretory and absorptive surfaces.

  1. Squamous Epithelium consists of a layer of thin, flat, scale-like cells with prominent nuclei. The cells have irregular boundaries that loosely into those of neighbouring cells. It forms the inner lining of lung alveoli and is involved in functions like forming a diffusion boundary and prevents underlying parts from injury.
  • Cuboidal Epithelium has cells which are polygonal in outline, but appear cuboidal in vertical section. It covers salivary and pancreatic ducts and thyroid vesicles.
  • Columnar Epithelium is characterised by the presence of tall elongated shaped like polygonal columns. Columnar epithelium covers the inner surface of the intestine, stomach and gall bladder. It also occurs in gastric and intestinal glands. Its function is secretion or absorption. The intestinal mucosa is lined by Brush-Bordered Columnar Epithelium which is highly absorptive.
  • Ciliated Epithelium consists of columnar or cubical cells bearing cilia on their free surfaces. The function of the cilia is to move particles, free cells or mucus in a specific direction over the epithelial surface. Ciliated epithelium lines the inner surfaces of some hollow organs such as Fallopian tubes, bronchioles and small bronchi. Ciliated columnar epithelium lining the ventricles of brain and spinal canal is called as ependyma. Cilia is of two types (i) Kinocilia are motile cilia with 9 + 2 organisation, (ii) Stereocilia — Basal granule absent, non-motile, 9 + 2 organisation is absent. Stereocilia are found in some parts of the male reproductive tracts such as the epididymis and Vas deferens.
  • Pseudostratified Epithelium covers the inner linings of trachea and large bronchi. Although made up of a single layer of columnar cells, it appears two-layered, because some cells are shorter than the others and have their nuclei at a different level. The shorter cells lack cilia and secrete mucus which traps particles on the epithelial surface. The longer cells are ciliated. The ciliary movement propels the mucus and the particles towards the larynx.



Cells of the epithelium are set very close to each other, separated by very thin films of extracellular material. Neighbouring cells are held together by cell junctions. The epithelial tissue rests on a non-cellular Basement Membrane, which separates it from the underlying connecting tissue.

The basement membrane is a non-cellular membrane made up of two layers.

Upper thin layer called as basal lamina made up of glycol-proteins and muco-polysaccharides secreted by epithelial cells.

Lower thick fibrous layer also called as Reticular lamina, made up of reticular fibers and collagen fibers which are the part of underlying connective tissue.

Blood vessels are absent in the epithelial tissue. Materials are exchanged between epithelial cells and vessels of the connective tissues by diffusion across the basement membrane. The epithelial tissue is classified into simple and compound epithelia.



A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. The particles in suspensions are bigger than 100 nm to 200 nm across. The particles of a suspension may not be visible to the naked eye but are visible under a microscope. Such as: Milk of magnesia is a suspension of magnesium hydroxide in water.


  • Suspensions are heterogeneous systems.
  • They stay only for a limited period. i.e. these are not stable as the particles have a tendency to settle down under the influence of gravity.
  • The particles of a suspension can neither pass through ordinary filter paper nor through animal membranes. Examples of suspensions are sodium chloride in benzene, turmeric in water, silver chloride, barium sulphate or sand in water.

class 9, science, types of solution

types of solution

  1. Solid solutions: in which solid is the solvent while solute can be either a solid, liquid or a gas. Such as alloys {jewellery of gold (solid in solid)}, hydrated salts (hydrated copper sulphate), etc.
  2. Liquid solution: in which liquid is the solvent while solute can be solid, liquid or gas. Such as: a solution of sugar in the water(solid in liquid), a solution of alcohol in water(liquid in liquid), aerated drinks(gas in liquid)
  3. Gas solution: in which gas is the solvent while solute can be either a solid, liquid or a gas. Such as: camphor in air, clouds, fog, air, etc.  


  • Saturated Solution: A solution in which no more solute can be dissolved at a given temperature is called a saturated solution.
  • Unsaturated solution: A solution in which more solute can be dissolved at a given temperature is called an unsaturated solution.
  • A given solution that is saturated at a particular temperature may become unsaturated when the temperature is increased.


Solubility of solids in liquids: When a saturated solution at a particular temperature (say room temperature) is heated, it becomes unsaturated. This is because the solubility of a substance generally increases with increase in temperature and hence more solute can be dissolved on increasing the temperature. If a saturated solution, at a particular temperature is cooled, then some of the dissolved solute will separate out in form of crystals. This is because solubility of solute in the solution decreases on cooling.

Solubility of gases in liquids: The solubility of gases in liquids increases on decreasing the temperature or decreases on increasing the temperature. For example, water contains dissolved oxygen. When water is boiled, the solubility of oxygen in water decreases and the excess oxygen escapes in form of bubbles.


  • An increase in pressure increases the solubility of a gas. Example: aerated water bottles contain carbon dioxide gas under pressure.


  • Increase in temperature increases the solubility. Example: it is easier to dissolve sugar in hot milk than in cold milk.

what are solution and their properties


Solution is defined as a homogeneous mixture of two or more chemical substances.

  • A Solution is a homogeneous mixture of two or more substances. These substances can be in any of the three physical states. For example, common salt in water (liquid solution), air (gaseous solution), alloys (solid solution), etc.
  • The components of a solution may be classified as: Solute & Solvent
  • There are two types of solution: Aqueous solutions & Non-aqueous solutions. Aqueous solutions: Solutions that contain water as the solvent are called aqueous solutions. For example, sugar in water, carbon dioxide in water, etc.  Non-aqueous solutions: Solutions that contain a solvent other than water are called non-aqueous solutions. Ether, benzene, petrol, carbon tetrachloride etc., are some common solvents. For example, sulphur in carbon disulphide, naphthalene in benzene, etc.

General properties of solution

  • Appearance: Clear and transparent, especially in dilute form.
  • Sub-division of particles: The solute breaks up into tiny particles, which could even be of ionic or molecular size. Solute particles become too small as compared to the pores of a filter paper and they pass through filter paper.
  • Sedimentation of particles does not occur in a solution: The particles of the solute in the solution will not settle down. A true solution can be preserved for any length of time without any sedimentation taking place. Seas and oceans have contained sodium chloride since millions of years, but crystals of salt cannot be seen on the sea-bed or ocean-bed.
  • Homogeneity: Solutions are homogeneous in character. If you add a pinch of salt to a glass of water, the particles of salt spread out evenly throughout the water.
  • No definite composition: A solution is a mixture. Mixtures of the same substances can be mixed in varying proportions. Hence, solutions do not have any definite composition.