CELL SIZE & CELL SHAPES

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CELL : STRUCTURE AND FUNCTIONS

CELL SIZE & CELL SHAPES

CELL SIZE

• There is a wide variation in the size shaped and activities of cells . 
• The smallest cells are those of Mycoplasma . They have a size of 0.1-0.5 micro meter 
• Bacteria measure 3-5 micro meter  in length . 
• Viruses are still smaller . They do not have a cellular structure . 
• The smallest virus has a volume of 7.0 x 10-7 micro meter³ . 
• The smallest mycoplasma has a volume of 10 x 10‐³ micro meter³  ' while the smallest bacterium possesses a volume of 2.0 x 10‐² micro meter ³.
• Unicellular eukaryotes have a size of 1-1000 um 
• Sporozoite of Plasmodium is only 2 um long . 
• Cells of multicellular eukaryotes have a size range of 5-100 um . 
• Among multicellular organisms , human erythrocytes ( RBC ) are about 7 um in diameter . 
• Some lymphocytes are still smaller.
• Cells of kidney , liver , skin and intestine are 20-30 micro meter  in diameter . 
• Muscle and nerve cells are comparatively very large . 
• A striated muscle cell can be 1- 40 mm long and 30-80 um in thickness . 
• Longest cells of human body are the nerve cells which may reach a length of 90cm Amongst plants , large cells occur in many algae . 
• Intemodal cells of Chara are 1-10 cm in length . 
• Acetabularia, a unicellular alga , is up to 10 cm in length . 

• In general , eggs are large sized cells because they store food for partial or complete development of the embryo . 
• Human egg is slightly over 0.1 mm or 100 um in diameter .  
• Avian eggs are the largest . 
• Hen egg is 60 x 45 mm with a volume of 5.0 x 100 um 
• The egg of Ostrich is 170 x 150 mm 

CELL SHAPES

• The cells vary in their shapes . 
• They may be disc like , polygonal , columnar , cuboid , amoeboid , thread like or irregular . 
• The shape of cell is related to its position ( flat in surface cells , polygonal in cortex ) and function ( e.g. , RBCs are biconcave to pass through capillaries and carry O2 
• WBCs are irregular to do phagocytosis , nerve cells are long lo conduct impulses , sperms have tail for motility etc. 

• On the basis of organization of DNA , the cells are of two types , prokaryotic and eukaryotic . 
• The organisms having prokaryotic cells are called prokaryotes . 
• They are now a - days placed in a super kingdom called Prokaryote . 
• Other organisms ( having eukaryotic cells ) are included in super kingdom Eukaryote . 
• Prokaryotic cells occur in bacteria , blue green algae , chlamydiae , Archaebacteria and Mycoplasma or PPLO.

The factors which set the limit of cell size or volume are : 

• Nucleo - cytoplasmic or kern - plasma ratio ( ratio of nucleus to cytoplasm) which determines the range of control of metabolic activities by nucleus . 
• Ability of oxygen and other materials to reach every part of the cell . 
• Ability of waste products to pass to the outside .
• Rate of metabolic activity .
• Ratio of surface area to the volume of the cell

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