Chapter Chosen

Cell : The Unit of Life

Book Chosen


Subject Chosen


Book Store

Download books and chapters from book store.
Currently only available for.
CBSE Gujarat Board Haryana Board

Previous Year Papers

Download the PDF Question Papers Free for off line practice and view the Solutions online.
Currently only available for.
Class 10 Class 12
 Describe history, location, types of ribosomes.

History. Ribosomes were first seen as granules by Cluade in 1941. Originally they were named as microsomes but the term ribosome was introduced by Palade in 1955.

Location. The ribosomes are the only organelles which are universally found in all cells i.e. prokaryotic and eukaryotic cells. In prokaryotic cells they are found freely floating in the cytoplasm, while in eukaryotic cells they are are usually found attached at the outer surface of endoplasmic reticulum. 

Shape and size. They are oblate spheroidal in form and have size of 18nm in bacteria, chloroplasts and mitochondria and 30 nm in eukaryotic cell.

Types. Ribosomes are of two basic types, 70S and 80S ribosomes. The ‘S’ refers to Svedberg units . 80S ribosomes are found in eukaryotes.  while the 70S is found in prokaryotes. The 70S ribosome is has 50S and 30S units whereas 80S is made up of 60S and 40S units. 





Who reported that the cell had an outer layer which is known as plasma membrane today?

Theodore Schwann 

State one difference between gram positive and gram negative bacteria.

Gram positive bacteria retains the gram stain whereas the Gram negative bacteria does not. 

Who concluded, “Cells are the ultimate units forming the structure of all plant tissues”?

Mathias Schleiden.

What is the function of contractile vacuole in amoeba?


 What are receptor molecules ?

Receptor molecules are specific proteins in the cell's plasma membrane that receive chemical signals from outside the cell. When such chemical signals bind to a receptor, they cause some form of cellular response.