Fundamental Unit of Life:-

                                   Chapter-5

                                  Fundamental unit of life

Introduction

• Cell is the structural and functional unit of life. It is the basic unit of life.

• It is discovered by Robert Hook in 1831 in cork slice with the help of primitive microscope.

• Leeuwenhoek (1674), discovered the free living cells in pond water with the improved microscope.

• Robert Brown discovered the nucleus in the cell in 1831.

• Purkinje coined the term ‘protoplasm’ for the fluid substance of the cell in 1839.

The cell theory

• The theory that all the plants and animals are composed of cells and the cell is the basic unit of life, was presented by two biologists, Schleiden and Schwann.

• The cell theory was further expanded by Virchow by suggesting that all cells arise from pre-existing cells.

→ Types of organisms

• On the basis of no. of cells, organisms are of two types:
(i) Unicellular Organism
(ii) Multicellular Organism

(i) Unicellular Organism: These organisms are single celled which perform all the functions. Example: Amoeba, paramecium, bacteria.

(ii) Multicellular Organism: Many cells grouped together to perform different function in the body  and also form various body parts. Example: fungi, plants, animals.

• The shape and size of cell are different according to the kind of function they perform. There is division of labour in cells.

• Each cell has certain kind of cell organelles to perform different type of function like mitochondria for respiration.

→ Types of cells

• There are two types of cells:
(i) Prokaryotes
(ii) Eukaryotes

Prokaryotes	Eukaryotes
Cells of organism lacks nuclear membrane.	Cells of organism have nuclear membrane.
Nucleolus is absent.	Nucleolus is present.
Single chromosomes.	Single or multi chromosomes
Reproduction is always asexual.	Reproduction is both sexual and asexual.
Always unicellular.	Often multicellular.
Membrane bound cell organelles are absent.	Membrane bound organelles are present like mitochondria.
Centriole is absent.	Centriole is present only in animals cell.
Cell division is by binary fission.	Cell division is by mitosis or meiosis.
Example: Bacteria, Blue green algae, etc.	Example: Fungi, Plant cell, Animal cell etc.

Difference between Animal cell and Plant cell

Animal Cell	Plant Cell
Cell wall is absent.	Cell wall is present.
Plastids are absent.	Plastids are present.
Centrioles are present.	Centrioles are absent.
Golgi bodies are present.	Golgi bodies are present and called dictyosome.
Vacuoles are absent. If present, they are small.	Vacuoles are present and large in size.
Centrosome is present with one or two centrioles.	Centrosome is absent

Diffusion

• The spontaneous movement of a substance from a region of high concentration to the region of low concentration is called diffusion.

• Some substances like carbon dioxide or oxygen can move across the cell membrane by a process called diffusion. Cell also obtains nutrition from the environment.

Osmosis

• The movement of water molecules through selectively permeable membrane along the concentration gradient is called osmosis.

• Plant cell tend to obtain water through osmosis.

Plasma membrane or Cell membrane

• This is the outermost covering of the cell that separates the contents of the cell from its external environment.

• The plasma membrane allows or permits the entry and exit of some materials in and out of the cell.

• It also prevents movement of some other materials. The cell membrane is called selectively permeable membrane.

• It is made up of lipid and protein.