Organization of cells
Cells are the basic structural and functional unit of all organisms.
There are two kinds of cellular organization
Bacteria and Archaea are prokaryotic cells. All the other organisms have eukaryotic cells.
All cells share certain basic features. They are;
Difference between prokaryotic and eukaryotic cells
| Feature | Prokaryotic cells | Eukaryotic cells |
| Organisms | Bacteria
Archaea bacteria |
Protista, fungi, plants, animals |
| Cell size | Average diameter (1-5 micrometre) | 10-100 micrometre |
| Form | Mainly unicellular | Mainly multicellular (except Protista and fungi many of which are unicellular) |
| Evolutionary origin | 3.5 billion years ago | 1.8 billion years ago, evolved from prokaryotes |
| Cell division | Mostly binary fission
No spindle formation |
Mitosis, meiosis or both
Spindle form |
| Genetic material | DNA is circular and lies freely in the cytoplasm
This region is called nucleoid. DNA is naked, not associated with proteins or RNA to form chromosomes |
DNA is linear and contained in a nucleus.
DNA is associated with proteins and RNA to form chromosomes |
| Type of ribosomes | 70s ribosomes (smaller) | Both 70s and 80s ribosomes (larger) present, may be attached to endoplasmic reticulum |
| Organelles | Few organelles, none are surrounded by membrane.
Internal membranes scares; if present usually associated with respiration, photosynthesis and N2 fixation |
Many organelles, membrane bounded organelles found. Great diversity of organelles. E.g.-
· Nucleus, mitochondria, chloroplasts bound by two membranes. · Lysosomes, vacuole, microbodies are bounded by single membrane |
| Cell walls | Bacteria – Peptidoglycan
Archea – Polysaccharide and protein |
Cell walls of plants and fungi are rigid and contain polysaccharides; cellulose is the main strengthening compound of plant cell walls
Chitin of fungal walls Cell wall is absent in animal cell |
| Flagella | Simple, lacking microtubules; extracellular.
Not enclosed by cell surface membrane 20nm diameter |
Complex with 9+2 arrangement of microtubules.
Inter cellular, surrounded by cell surface membrane 200nm diameter |
| Respiration | Mesosomes in aerobic bacteria, except cytoplasmic membranes in cyanobacteria | Mitochondria for aerobic respiration |
| Photosynthesis | No chloroplasts.
Take place on membranes which show no stacking |
Chloroplasts containing membranes which are usually stacked into lamella or grana |
| Nitrogen fixation | Some have the ability | Non have the ability |
