TOPIC INDEX BIOLOGY/NCERT/ISBN 81-7450-496-6/P125/8.1
INTRODUCTION TO CELL AND PROKARYOTIC CELLS
- · Cell is the fundamental structural and functional unit of a living organism.
- · Cell theory states that :-
1. All living organisms are composed of cells and products of cells.
2. All cells arise from pre-existing cells.
- Cell has dense membrane bound structure called nucleus which contains chromosomes, which in turn contains DNA (genetic material).
- · Cells that have membrane bound nuclei are called as eukaryotic cells, while the cells which lack membrane bound nucleus are called as prokaryotic cells.
- · Eukaryotic cells have other membrane bound organelles like Endoplasmic Reticulim(ER), the golgi complex, lysosomes, mitochondria, microbodies and vacuoles. These are absent in prokaryotic cells.
- · RIBOSOME:- It is a non- membrane bound organelle found in both eukaryotic and prokaryotic cells.
- · Ribosomes are also found in chloroplasts(in plants), mitochondria and on Rough Endoplasmic Reticulum(RER) .
- · CENTRIOLE:- It is a non- membrane bound organelle in animal cells, which hels in cell division.
- · MYCOPLASMAS:- These are smallest cells.
- · Egg of ostrich is largest isolated cell.
- · Nerve cells are some of the longest cells.
PROKARYOTIC CELLS
- · They are represented by bacteria, blue- green algae, mycoplasma and PPLO(Pleuro Pneumonia Like Organism).
- · Smaller and multiply more rapidly than Eukaryotic cells.
- · 4 basic shapes of bacteria- Bacillus(rod like), Coccus (spherical), Vibrio (comma) and spirillum (spiral).
- · Prokaryotes have a cell wall surrounding the cell membrane except in mycoplasma.(Execption)
- · No well defined nucleus.
- · Genetic material is basically naked.
- · Plasmids:- Many bacteria have small circular DNA outside the genomic DNA called plasmids.
- · UNIQUE FEATURE:- A specialized differentiated form of cell membrane called mesosome is the charcterstic feature of prokaryotes. They are infoldings of cell membrane.
