1. Bacteria are microscopic, smallest (0.2-5.0 micrometers) and simplest organisms.
2. They are unicellular organisms. But can form groups or colonies together.
3. They are primitive creatures. That is, their nucleus does not have nuclear membrane and nucleolus.
4. Their cells contain no other organelles except ribosomes (70S). That is, bacteria do not have chloroplasts, mitochondria, endoplasmic reticulum, Golgibodies, lysosomes, cytoskeleton, microbodies etc.
5. They can be parasitic, saprophytic or autophytic.
6. Their cell wall is composed of mucopeptide, peptidoglycan, polysaccharide, teichoic acid and muramic acid. They are similar to plants because they have cell walls.
7. Their cell membrane or plasma membrane folds to form mesosomes.
8. They are very sensitive to phage virus.
9. They collect energy by oxidizing inorganic salts.
10. They can survive extremely cold temperatures ranging from -170C to 800C.
11. Cells of autophytic bacteria contain bacteriochlorophyll, bacterioviridin, bacterium chlorophyll and carotene as photosynthetic pigments.
12. As their cells do not have chromosomes, mitosis and meiosis cell division does not occur.
13. They reproduce by binary fission, asexually, asexually and sexually.
14. It can carry out respiration in the presence or absence of oxygen.
15. Some bacteria are obligate aerobic, some bacteria are obligate anaerobes and some bacteria are opportunistic anaerobes.
16. Bacterial cells have flagella. It is composed of flagellin protein.
17. Bacteria have pili or phimoxy. It is composed of pilin protein.
18. Its cell membrane does not contain cholesterol or steroids.
19. Forms endospores to survive in hostile environment. In this condition it can last up to 50 years.
20. They can usually have a basic color (gram positive or negative).