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

Chapter: 5

What Are The Fundamental Unit Of Life ?

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1. Cell

Smallest structural and functional unit of life.

Discovery of cell and its components	Cell theory	Types of cells on basis of organization	Types of organisms on basis of number of cells
Robert Hooke (1665) first observed dead cells in a cork slice.	Formated by M.J Schleiden (1838) and Theodor Schwann (1839) expended by R. Virchow (1855) all cells arise from pre-existing cells.	Prokaryotic cells organism without definite nucleus of bacteria.	Unicellular (single cell)
A. V. Leeuwenhoek (1674) discovered free living cells in pond water.	All living organisms are made up cells.	Eukaryotic cells organisms without definite nucleus, e.g., fungi, plants , animals
Robert Brown (1831) discovered the nucleus in the cell.	The cells is the basic structural and functional unit in all organisms.
Purkinje (1839) coined the term ‘protoplasm’.	All cells arise from pre-existing cells.

2. 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)

3. Osmosis

“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