CLASS 6TH | CELL- THE STRUCTURE AND FUNCTIONS | REVISION NOTES

Cell – it is the basic structural and fundamental unit of an organism. These are
called building blocks of our body.

Discovery of Cell – The term cell is first coined by an English scientist Robert
Hook in 1665. He used microscope to see a thin slice of dead cork. In this slice,
he observed some honeycomb like structures and he named them cell.

Microscope – A device used to see very tiny objects that are not visible to
naked ayes.

Cell theory – On the basis of remarkable findings, the basic features of modern
cell theory states that –
a. All living things are made up of one or more cells.
b. Cells are the basic structural and functional unit of organisms.
c. The chemical composition and metabolic processes of all the cells is
same.
d. All new cells are arises by the division of pre-existing cells.

Number, Shapes and Size of the Cell – Cells greatly differ in their shape, size
and number like organism such as bacteria is made up of single cell. Hence,
called unicellular and organism which are made up of multiple organism like
humans are called multicellular organisms.

• Cells can be irregular, oval, oblong, elongated and thread like in shape.
• Mostly cells are microscopic.
  Cell – the structural unit of life
  Cells vary in their shape, size and number. However, the basic structural
  components are same. Every organism like plants, animals and humans are
  made up of cells.
  Cell – the functional unit of life
  All the life processes performed by our body are due to the activity of cells
  present in our body. Example – root cells of plant absorb water and mineral
  from the soil.
  

Basic structure of the cell –

The prime components of a cell are –

1. Cell membrane – It forms the outer boundary of the cell. It is known as
   plasma membrane in plant cell. It is living.
2. Cell wall – It is the outermost protective layer of a cell. It is non-living.
3. Nucleus – It is the small spherical mass present in the centre of
   cytoplasm. It has a surrounding membrane called nuclear membrane. It
   contains chromosomes. It regulates and controls various activities in a
   cell.
4. Cytoplasm – It is a semi-liquid substance enclosed by cell membrane.
5. Cell Organelles – Some of the main cell organelles present in cytoplasm
   are –
   i. Endoplasmic reticulum
   ii. Ribosome
   iii. Mitochondria
   iv. Golgi bodies
   v. Lysosome
   vi. Centrosome
   vii. Plastids
   viii. Vacuoles