Notes of class 7

Chapter- Tissues

Tissue :-  Tissue is the group of structurally similar cells that perform similar function.

 In multicellular organisms the tissue group together to form different levels of organizations.

 Organization :- Organization is the manner in which smaller units of any structure or system are arranged into larger units in an hierarchical fashion.

In multicellular organism the level of organisation is important because of division of labour i.e. an organ system perform a specific function ( e.g. digestive system is for nutrition , Respiratory system is for breathing and respiration etc. ). There is a unique coordination among all organ system of an organism.

Atom, Molecule and macromolecule in level of organisation :-
The cell is starting of life. The cells are made up of many macromolecules like carbohydrate, Protein, fat, Nucleic acid etc. These macromolecules are combination of molecules, like :-
                 MACROMOLECULE                 MOLECULE
                 Carbohydrate                                   Glucose
                 Protein                                            Amino acid
                 Fat                                                   Fatty acid
                 Nucleic acid                                    Nucleotide

Now, molecules are made up of atoms like C, H, O, N, P, S, Na, Cl etc.
so, atom is starting point of level of organisation.

Cellular level of organisation :-
Macromolecules club together to form first signal of life called cell. In unicellular organisms like amoeba, bacteria etc. all life activities take place within single cell. 
In multicellular organisms like sponges, Algae cells group together but they do not form tissue. There is no division of labour.
So, these are representing cellular level of organisation.

Tissue level of organisation :-
In complex multicelllar organisms there is beginning of division of labour. The cells group together and perform specific functions. e.g.-

       CELL                               FUNCTION               TISSUE
        Nerve cells                                Conduct message          Nervous tissue
        Muscle cells / Muscle fibre       Contraction                   Muscle tissue