The Fundamental Unit of Life Class 9 Notes Science - Chapter 5

Chapter: 5

What Are The Fundamental Unit Of Life ?


Smallest structural and functional unit of life.

Discovery of cell and its components 

  • Robert Hooke (1665) first observed dead cells in a cork slice.
  • A. V. Leeuwenhoek (1674) discovered free living cells in pond water.
  • Robert Brown (1831) discovered the nucleus in the cell.
  • Purkinje (1839) coined the term ‘protoplasm’.

Cell theory

  • Formated by M.J Schleiden (1838) and Theodor Schwann (1839) expended by R. Virchow (1855) all cells arise from
    pre-existing cells.
  • All living organisms are made up cells.
  • The cells is the basic structural and functional unit in all organisms.
  • All cells arise from pre-existing cells.

Types of cells on basis of organization

  • Prokaryotic cells organism without definite nucleus of bacteria.
  • Eukaryotic cells organisms without definite nucleus, e.g., fungi, plants , animals 

Types of organisms on basis of number of cells

  • Unicellular (single cell)
  • Multicellular (large number of cell)


2.1 Cell Wall (Plant Cell)

  • Made up of cellulose, porous to micro and macro moleculose like sugar and starch.

2.2 Cell membrane

  • Made up of proteins and lipids.
  • Selectively permeable in nature.
  • Singer and Nicolson gave the fluid mosaic model of plasma membrane.

2.3 Protoplasm

  • Cytoplasm
  • ➥ Cell organelles
  • (i) Mitochondria ‘Power house of the Cell’
  • (ii) Ribosome site for protein synthesis
  • (III) Chloroplast (in green plants)
  • (a) Grana
  • (a) (i) Contain chlorophyll
  • (b) Stroma
  • (b) (i) Contain enzymes
  • (iv) Endoplasmic Reticulum
  • (c) Rough Endoplasmic Reticulum [RER] (with ribosomes)
  • (d) Smooth Endoplasmic Reticulum [RER] (no ribosomes)
  • (v) Golgi body (Processing and packaging proteins and other molecules to form cell secretions
  • Nucleus
  • ➥ Nucleoplasm
  • (i) Fluid medium (containing nucleotides and enzymes)
  • (ii) Chromatic substances/ chromoromes
  • ➥ Nuclear membrane

2.4 Vacuole (Plant cell)

  • Contains water, nutrients, mineral, salts, waste (with greeneous substances)


“Osmosis is a process by which the molecules of a solvent pass from a solution of low concentration to a solution of high concentration through a semi-permeable membrane.”

Isotonic solution Same concentration of solutes both inside and outside the cell. Cell will stay same size
Hypertonic solution Higher solute concentration outside the cell then inside Cell becomes flaccid or undergoes plasmolysis Exosmosis
Hypotonic solution Higher solute concentration inside the cell than outside. Cell becomes turgid or undergoes deplasmolysis endosmosis