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The fundamental unit of Life -CBSE CLASS 9


The fandamental unit of life



A cell is the smallest functional unit of life .Which is discovered by Robert Hooke in 1665. It can independently perform all necessary activities to sustain life . Therefore cell is the basic unit of life or the fundamental unit of life. Cells are two types of cells . plant cell and animal cell. Cell have different cell organelles . cell organelles are subcellular structure that has one or more specific jobs to perform in the cell.

Cell Theroy

Cell theory was given by three scientist named: Matthias Schleiden, Theodore Schwann and Rudolf Virchow

Matthias Schleiden concluded that all plant are mande of cell (1838).
Theodore Schwann concluded that all animals are mande of cell (1839).
Rudolf Virchow concluded that all cell came from pre-existing cell (1855).

Conclusion of cell theroy

  1. All living things are made up of cells.
  2. Cells are basic unit of structure and function in an organism.
  3. New cells are produced from pre-existing cell.

Structural organisation Of organism

Every organism is made up of cell , a group of cell makes up tissue, a group of tissue make up organs, a goup of organs makes organ system and group of organ system makes up organism.
Molecules → Cells → Tissues → Organs → Organ Systems → Organisms(body of an organism)

Size of cell

Prokaryotes and Eukaryotes

Prokaryotic Cell:- Pro means primitive and karyot means nucleus, The cells having primitive nucleus are called prokaryotic cells.They were the only means of living for billions of year. The DNA is present in the cytoplasm rather than in a nucleuuar bounded area. They are really small in size and have simple structure.
Eukaryotic Cell:- Eu means true and karyot means nucleus, the cells having true nucleous are called eukaryotic cells. They are not primitive and were made 2.7 billion years ago. The DNA is present in a nucleuar bound organelle rather then in cutoplasm. They are bigger in size as compared to prokaryotic cells. They have a complex structure.

Three main components of all cell

  1. Plasma Membrane
  2. Nucleus
  3. Cytoplasm

Plasma Membrane


  • Keeps a cell intact
  • Protective barrier
  • Regulate transport in & out of cell. This properrty is called selectively permeable.
  • Small lipid-soluable molecules, e.g. oxygen and carbon dioxide can pass easily.
  • Water can freely cross the membrane.

Phospholipid bilayer:-

Phospholipid bilayer is the structure of cell membrane. Lipid bi-layer is made of lipid + proteins, It has two ends. The top one is polar end and hydeophillic or water loving. The other end is non-polar or phydeophobic or water hating. This whole structure is living in nature.

Transport :- diffusion and osmosis

Diffusion:- Movement of sustance from high cocentration to lower concentration.
Osmosis:-It involves movement of solvent (water) molecules from the region of lower concentration of solute to the higher concentration of solute.

Concntration of Liquids

There are three types of solution on the basis of concentration of solution:-hypotonic, isotonic and hypertonic.
1. Hypotonic solution:-Relatively high water & low solute concentration. When a cell is kept inside a hypotonic solution then it wil swell up. Inside going of water is called endosmosis.
2. Isotonic Solution:-Equal amount of solute and solvent. When a cell is kept inside a isotonic solution it will remain in same size, it will not swell or shrink.
3. Hypertonic Solution:- High concentration os solute and less water. When cell kept in hypertonic solution it will shrink. Outside going of water is called exosmosis. When RBCs shrink it is called crenation.

Plasmolysis:- When a plant cell is placed in hypertonic solution the protoplasm(nucleus + cytoplasm) will shrink while the cell wall intact his is called plasmolysis. Plasmolysis and osmosis can be performed in living cell.

Cell Wall


  • It gives cell protection from harsh climatic conditions.
  • It maintains shape of cell.
  • It protects the cell busting.

  • rigid and tough. example:- wall of the room
In plant cell wall is made up of cellulose, in fungi cell wall is made up of chitin and in bacteria peptidoglyon.



  • controls all metabolic activities
  • Takes part in formation of ribosomes
  • directs synthesis of proteins
  • transmission of hereditary traits


The fluid present inside the cell but outside the nucleous is called cytopplasm. All cell orgenelles are suspended in the cytoplasm. It is composed of water, salt and various organic molecules.

Endocytosis and Exocytosis

Endocytosis:-The movement of macro particles from outside environment into the cell. It is involved in taking nutrients from outside the cell. It is not involved in cell wall formation.
Exocytosis:-The movement of macro particles from cell to the outside enviroment. It is involved in the removing of the waste from the cell. It is involved in cell wall formation.

Imporatnt cell organalles and their function

Some important cell organelles, and the functions of each may be defined as below;
1. Plasma membrane:Also called the cell membrane.Separates contents of the cell from its surroundings and regulates the entry of certain solutes.
2. Cell wall:Gives rigidity and shape to the plant cell.Allows substances to enter and leave the cell without hindrance.
3. Cytoplasm:All metabolic activities occur in the cytoplasm.
4. Endoplasmic Reticulum:Synthesis and transport of proteins and fat.Supportive framework for the cell.
5. Mitochondria:Synthesis of respiratory enzymes. Release of energy from pyruvic acid produced in the cytoplasm.
6. Golgi apparatus:Synthesis and secretion of enzymes and hormones.
7. Ribosomes: Protein synthesis
8. Lysosomes: Intracellular digestion
9. Centrosome: Initiates and regulates cell division
10. Plastids:Chromoplast imparts colour to the flowers and fruitsChloroplast traps solar energy for photosynthesis.Leucoplast stores starch
11. Nucleus: regulates cell functions
12. Nucleolus: produces ribosomes

Cell divison

Test your understanding


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