Complete O/L notes biology: CHP.4 Bacteria

Complete O/L notes biology: CHP.4 Bacteria

Complete O/L notes biology: CHP.4 Bacteria



Bacteria are unicellular microscopic organisms. They are a lot bigger than viruses

4.1. Classification of bacteria

Kingdom: Monera

Phylum: Eubacteria

Class: Schizomycetes

Genus: Escherichia

Specie: Coli

Scientific name: E. coli

                Bacteria can be found in many different shapes and form. They can be found everywhere on plants, on clothes, in the air, on furniture not all Bacteria causes diseases. Those who causes diseases are called pathogenic bacteria and those that do not are called nonpathogenic bacteria.

4.2. Forms of Bacteria

Bacteria many be found having a round shape and this is called Cocci forms. The cocci forms can be found in dingles or it can be found in twos called diplococcus or it can be found in chains called streptococcus or it can be found in bundles called staphylococcus.

Fig: Forms of bacteria

General structure of a bacteria


Bacteria has a cell wall which is made up of carbohydrate fats and proteins. In plants, the cell wall is made up of cellulose bacteria is enclosed in a slime mold or slime capsule. The cytoplasm is alkaline in nature and it contains substances such as sugar, fat, proteins and most of these are colorless. Some bacteria have flagella for locomotion while others do not have.

Bacteria may either be parasite or saprophytic (they live on death organism) and parasite may live in or on other living organism called the host while saprolite live on death organism and the cause decay.

4.3. General characteristics of bacteria

  1. Bacteria are microscopic and are the smallest cellular organism
  2. Their cell wall is made of chitin and protein
  3. Bacteria doesn’t have a definite nucleus but it has nuclear material without a nuclear membrane.
  4. Bacteria may be motile or non-motile
  5. The nutrition is either autotrophic, parasitic, saprophytic and autotrophs.
  6. Respiration is either aerobic (need oxygen) or anaerobic (do not need oxygen)
  7. Some bacteria cause diseases to plant and animals (pathogenic) while others do not.

4.4. Reproduction in bacteria

Reproduction in bacteria is asexual by binary fission (the nucleus divides, the cytoplasm divides and two new organisms are formed.

4.5. Respiration in bacteria

Bacteria respire either aerobically or anaerobically

4.6. Excretion in bacteria

Bacteria sends out waste product e.g. co2 and other poisonous waste called toxins.

4.7. Habitats of bacteria

Bacteria occurs in soil, dust, water, air, food, bodies of plants and animals and everywhere. Some can live in hot springs up to 60oc

4.8. Reproduction of Bacteria

Bacteria grows and multiply very rapidly at temperatures between 30oc and 37oc. when the bacteria reach full maximum size of growth it produces by an asexual method call binary fusion (the nucleus divides, the cytoplasm divides and two new bacteria are formed). This division occurs every 20 – 30 minutes.

4.9. Growth and multiplication of bacteria

When bacteria reach full seize of growth, it can multiply by binary fission. The growth is determined by the population of bacteria cell and the bacteria can multiply to form a colony of cell.

Fig: growth of bacteria.

The growth rate of bacteria is favored by temperature between 30 degree to 37 degree up to a maximum of 42 degree. The growth rate is affected by the presence or absence of nutrients and also the accumulation of waste nutrients needed four phases.

Fig: Growth of bacteria


4.10. Harmful effects of bacteria

  1. Bacteria causes diseases in animals e.g. tetanus, tuberculosis, pneumonia, cholera, typhoid, dysentery, notches, dysphoria. Diseases that can be caused by bacteria to plant are blight, center of citrus, blight of potatoes and tomatoes
  2. Bacteria causes food poisoning
  3. Bacteria brings about spoilage of food
  4. Bacteria brings about septic condition e.g. septic wounds
  5. Denitrifying bacteria reduces soil fertility
  6. Bacteria produces toxins which causes illness to plants and animals.

4.11. Useful effects of bacteria

  1. Purifying bacteria bring about decay which help to increases soil fertility
  2. Nitrifying bacteria and nitrogen fixing bacteria
  3. Bacteria can be used for making yoghurt butter, vinegar, cheese and vitamins
  4. Bacteria helps to digest cellos in the intestine of herbivores animals
  5. Bacteria is used for making antibiotics
  6. Bacteria is used for research
  7. Bacteria is used for netting (make fibers)

4.12. Economic importance of bacteria

  1. They cause diseases
  2. Bacteria phase helps to destroy harmful bacteria
  3. Viruses are used in producing vaccines
  4. They are important for research

4.13.    Control and prevention of bacteria

  1. Propper sanitation habits should be observed so that you don’t take in contaminated food or water
  2. Sterilized objects should in certain cases e.g. syringes should be sterilized
  3. Vaccination should be done with the correct vaccine
  4. Patients suffering from diseases like tuberculosis should be isolated in the hospital
  5. The population should be educated on the types of bacteria method of spread and control bacteria.

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