NCERT 9TH CLASS SCIENCE CHAPTER THE FUNDAMENTAL UNIT CELL

 

CYTOLOGY

    The cell and its structures are studied under a branch of biology called cytology.
    Definition :- The structural & functional unit of living beings is called cell. 

DISCOVERY OF CELL

    1.    Robert Hooke (1665) :– An English man and first curator of  
        Royal  society of London.
        Observed a thin transverse section of bark of a tree under self designed microscope.
        He noticed honey - comb like compartments.
        He coined the term cell .
        He wrote a book - Micrographia.        
        He actually observed dead cells.                    
    2.    Antony Van Leeuwenhoek (1674) was first to observe 
        living cells like bacteria [from tartar of teeth]
        erythrocytes [fish], sperms and protozoans [eg. Vorticella]
    3.    N. Grew (1682) :– Proposed cell concept which states that cell is unit of structure of organisms.
    4. Cell is called structural & functional unit of life because –
        (i)    All the living  organisms are composed of one or more cells. 
        (ii)    All the cells have similar basic structure.
        (iii)    Similar cell organelles of different cells perform  similar functions.

    5. Knoll and Ruska (1932) of Germany designed the electron microscope which was employed to study the ultrastructrue (fine structure) of cell and various cell organelles in 1940s.    

MICROSCOPE

   It is instrument which is used to study those objects that cannot be seen with the naked eye or with the help of a hand lens. A microscope has more than one lens. The 1st compound microscope was built by F. Janssen and Zacharias Janssen (1590).
²    Structure of Microscope: The microscope used in schools is called compound microscope, a compound microscope has following parts:
1 Base: It is the basal, metallic, horse-shoe shaped structure. It bears the whole weight of microscope.
2 Handle: It
Read More