CELL - PROKARYOTES AND EUKARYOTES

 CELL

·       Cell is defined as the basic structural, functional and biological unit of all living organisms.

·       The word “Cell” was derived from the Latin word “Cella” which means “Small Room”.

·       The cell was first discovered by the English Botanist Robert Hooke in 1665 from his microscope.

·       Cells can replicate independently and called as “Building blocks of life”.

·       The study of cell is “Cell Biology” or “Cytology”.

·       Living organisms can be classified as Unicellular organisms (Contains single cell) (Example - Bacteria, Yeast, Protozoa and Some algae) and Multicellular organisms (Contains multiple cells) (Example - Fungi, Algae, Plants and Animals).

CELL THEORY

·       In 1838, German Botanist Matthias Jacob Schleiden discovered the all the plants were composed of cells.

·       In 1839, German Zoologist Theodor Schwann discovered that all the animals were composed of cells.

·       In 1855, German Physician Rudolph Virchow found that all the cells come from pre-existing cells.

·       Cell Theory has 3 basic points

a)     All the living things are made up of one or more cells.

b)     The cell is the basic unit of life.

c)     All cells must come from pre-existing cells.

PROKARYOTES AND EUKARYOTES

The living cells can be divided into two distinct groups based on the nucleus structure:

Prokaryotes

The organism lacking true nucleus (membrane enclosed chromosome and nucleolus) and other organelles like mitochondria, golgi body, entoplasmic reticulum etc. are referred as Prokaryotes. (Example: Bacteria and Archaea).

Eukaryotes 

The organism possessing membrane enclosed nucleus and other cell organelles are referred as Eukaryotes (Example: Algae, Fungi, Protozoa, Animals and Plants).

Differences between Prokaryotic and Eukaryotic Cell

Features	Prokaryotes	Eukaryotes
Nucleus	Lack of true nucleus. No nuclear membrane or nucleoli	Contains true nucleus which consisting of nuclear membrane or nucleoli
Examples	Bacteria and Archaea	Fungi, Algae, Protozoa and Plants.
DNA composed with Histones (Alkaline proteins)	Absent	Present
Plasmids	Present	Rare
Chromosomes	One circular chromosomes	More than one linear chromosomes
Location of Genetic information	Nucleoid	Membrane enclosed Nucleus
Ribosomes	70 S Type (Divided into 2 sub-units: 50 S and 30 S)	80 S Type (Divided into 2 sub-units: 60 S and 40 S)
Nucleolus	Absent	Present
Mitochondria	Absent	Present
Chloroplasts	Absent	Present in plant and algae
Chromatophores	Present only in Photosynthetic bacteria	Absent
Endoplasmic reticulum	Absent	Present
Golgi apparatus	Absent	Present
Lysosomes	Absent	Present
Peroxisomes	Absent	Present
Sterols and carbohydrates in Plasma membrane	Absent	Present
Cytoskeleton in Cytoplasm	Absent	Present
Cell Division	Binary fission	Mitosis/Meiosis
Peptidoglycan	Present	Absent
Mesosomes	Present	Absent
Respiratory enzymes	Cytoplasmic membrane	Mitochondria
Mitotic spindle	Absent	Present during cell division
Cilia	Absent	Present
Pili	Present	Absent