Cells come in a variety of shapes and sizes that suit their diverse functions.
Along with their differences in size, cells present an array of shapes.
Cells may be disc–like, polygonal, rectangular, cuboid, thread–like, branched or even irregular. These shapes of cells are often related to the different functions they perform. Some, such as the bacterium Escherichia coli, resemble rods. An Amoeba has no definite shape or size, it is irregular in shape and it uses amoeboid movement as a form of locomotion. Sometimes the amoeba deforms its body into projections called pseudopods or “false feet”, which resembles like arms or feet that slide over the surface. Paramecium is a unicellular ciliate protozoan that resembles slipper shaped and the locomotion is through cilia.
Valonia ventricosa (Bubble algae) is among the largest unicellular species.
All living organisms present on earth can be classified into two types:
Non–cellular organisms which do not contain any cell in their body organization.
Eg: Viruses. Viruses lack any membrane and hence do not show characteristics of life until they enter a living body
(i.e., prokaryotic cell or eukaryotic cell) to use its cell machinery to reproduce.
Cellular organisms, which contain either one or many cells in their bodies, eg: Bacteria, plants and animals.
The basic structural and functional unit of every cellular organism is one of two types of cells prokaryotic
or eukaryotic. The term prokaryote comes from Greek words that mean “before nucleus” or
“prenucleus”, while eukaryote means “true nucleus”.
A unicellular organism, also known as a single–celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of multiple cells. Historically the simple single celled organisms have sometimes been referred to as monads. The main groups of unicellular organisms are bacteria, archaea, protozoa, unicellular algae and unicellular fungi.