What is Cell?

Cell is the basic structural and functional unit of life. The word 'cell' was first coined by British scientist Robert Hook in the year 1665. The smallest cell is Mycoplasma gallisepticum. The longest cell is Neuron. The biggest cell is egg of Ostrich.

Schilden and Schwan established cell theory in the year 1838-39. Features of the cell theory :
(i) All organism are composed of cell
(ii) Body of every organism is made of cell
(iii) Each cell arises from pre-existing cell
(iv) Every organism starts its life from single cell

Cell

Evaporation

Evaporation : The process of conversion of a liquid into its vapours at room temperature is called evaporation. Evaporation causes cooling.

Actually, during evaporation, the molecules having higher kinetic energy escape from the surface of the liquid. Therefore cooling takes place during evaporation because of temperature of liquid is directly proportional to average kinetic energy.

Evaporation

Evaporation is affected by following factors :

(i)   Nature of liquid

(ii)  Temperature

(iii) Surface area

Russian State Library

The "Russian State Library" is the national library of Russia, located in Moscow. It is the largest in the country and the third largest in the world for its collection of books (17.5 million). It was named the V. I. Lenin State Library of the USSR from 1925 until it was renamed in 1992 as the Russian State Library.
The library has over 275 km of shelves with more than 43 million items, including over 17 million books and serial volumes, 13 million journals, 350 thousand music scores and sound records, 150,000 maps and others. There are items in 247 languages of the world, the foreign part representing about 29 percent of the entire collection.
Between 1922 and 1991 at least one copy of every book published in the USSR was deposited with the library, a practice which continues in a similar method today, with the library designated by law as a place to hold a "mandatory" copy of every publication issued in Russia.

Sound Wave

Sound Wave : Sound waves are longitudinal mechanical wave. According to their frequency range, longitudinal mechanical waves are divided into the following categories :

(1) Audible or Sound Waves : The longitudinal mechanical waves which lie in the frwquency range 20 Hz to 20000 Hz are called audible or sound waves.
These waves are sesitive to human ear. These are generated by the vibrating bodies such as tuning fork, vocal cords etc.

(2) Infrasonic Waves : The longitudinal mechanical waves having frequencies less than 20 Hz are called Infrasonic.
These waves are produced by source of bigger size such as earth quakes, volcanic eruptions, ocean waves and by elephants and whales.

(3) Ultrasonic Waves : The longitudinal mechanical waves having frequencies greater than 20000 Hz are called ultrasonic waves.
Human ear can not detect these waves. But certain creatures like dog, cat, bat, mosquito can detect these waves. But not only detect but also produce ultrasonic.

Egyption Civilization

Egyption civilization : Egypt is called the 'Gift of the Nile'. Historians divided the history of Egypt into three periods; the Old Kingdom, the Middle Kingdom and the New Kingdom.

The Old Kingdom is also called the 'Age of the Pyramids'. The Egyption king was called the pharaoh. The Egyptions were the worshipper of the nature and sun was their most important god.