Prokaryotes • Mesokaryotes and • Eukaryotes . . Prokaryotes Those organisms with primitive nucleus are called as prokaryotes ( pro – primitive; karyon – nucleus). The DNA lies in the ‘nucleoid’ which is not bound by the nuclear membrane and therefore it is not a true nucleus and is also a primitive type of nuclear material.
The DNA is without histone proteins. Example: Bacteria, blue green algae, Mycoplasma, Rickettsiae and Spirochaetae. . .
Mesokaryotes In the year , scientist Dodge and his coworkers proposed another kind of organisms called mesokaryotes . These organisms which shares some of the characters of both prokaryotes and eukaryotes. In other words Virus . - .
µm Bacteria . - µm Plant cell - µm Chicken Egg 65mm RBC - µm BGA - µm Mycoplasma . - . µm Ostrich Egg - mm Ultra microscope Light microscope Naked Eye Figure .
: Cell size variation of few organisms Size: . . Plant and Animal cell . .
Ultra Structure of an Eukaryotic Cell An eukaryotic cell is highly distinct in its organisation. It shows several variations in different organisms. For instance, eukaryotic cells in plants and animals vary greatly (Figure . ).
Figure . : Animal and Plant cell Animal Cell Animal cells are surrounded by cell membrane or plasma membrane. Inside this membrane a gelatinous matrix called protoplasm is seen to contain nucleus and other organelles which include the endoplasmic reticulum, mitochondria, golgi bodies, centrioles, lysosomes, ribosomes and cytoskeleton. Plant cell A typical plant cell has prominent cell wall, a large central vacuole and plastids in addition to other organelles present in animal cell (Figure .
). Figure . : Ultra Structure of Plant Cell . .
Protoplasm Protoplasm is the living content of cell that is surrounded by plasma membrane. It is a colourless material that exists throughout the cell together with cytoplasm, nucleus and other organelles. Protoplasm is composed of a mixture of small particles, such as Comparison between types of cellular organisation Features Prokaryotes Mesokaryotes Eukaryotes Size of the cell ~ -5µm ~ -10µm ~ -100µm Nuclear character Nucleoid, no true