Microoraganisms In Action SS1 Biology Lesson Note

GROWTH OF MICRO-ORGANISMS

Bacteria reproduce by binary fission in which a single cell divides into two. This process is called asexual reproduction. The time interval required for the cell to divide into two is called generation time. This time varies from one organism to another.

It strongly depends upon nutrient availability, temperature, gaseous requirement and pH. There are different phases in the growth of bacteria. These include the:

(i) lag phase 

(ii) logarithmic or exponential phase 

(iii) the stationary  phase and 

(iv) decline or death.  

The growth of micro-organisms can be measured by using any of these methods:

1. Turbidity method.
2. Serial dilution method.
3. Squared transparent paper or cellophane method.

BENEFICIAL AND HARMFUL EFFECTS OF MICRO-ORGANISMS

1. BENEFICIAL EFFECTS

1. Bacteria help to digest cellulose in herbivores.
2. In men, they synthesize vitamin K and B12

iii. Bacteria and fungi are widely used in the synthesis of antibiotics

1. They are used to manufacture amino acids and vinegar
2. Bacteria are used to process milk into different tastes and flavours
3. They are used to decompose sewage into harmless inorganic compounds.

vii. Microbial cultures are used to produce enzymes

viii. Yeast is used as a leavening agent in baking industries.

1. Algae play an important role in fertilizing the soil. 
2. Bacteria are used to produce single-cell protein (SCP).

1. HARMFUL EFFECTS 

1. Bacteria cause decay and spoilage of food items.
2. Materials like wood, paper, textiles, rubber and metals are destroyed by microbes.

iii. They cause diseases of different types.

DISEASES CAUSED BY MICRO-ORGANISMS

ASSIGNMENT

1. The growth phase in bacteria in which cells divide steadily at a constant rate is called     

(a) Exponential phase     (b) lag phase      (c) stationary phase     (d) decline phase

2. Which of the following microbes causes cholera?      

(a) Virus    (b)Bacterium            (c) Protozoan    (d) Fungus

4. Growth of micro-organisms can be measured by the following methods except___________ method     

(a) serial dilution    (b) turbidity    (c) squared transparent paper      (d) dry weight

5. The following practices contribute to the control of the spread of diseases except   

(a) sewage treatment with chemicals       (b) proper sewage disposal    (c) disinfecting the surrounding       (d) using human faeces as manure

6. The vector of the trypanosome parasite is     

(a) housefly  (b) tsetse fly   (c) mosquito     (d) black fly

7. Define the following phases in microorganisms’ growth     

(i) lag    

(ii) exponential     

(iii) stationary.

8. State four ways in which each of the following organisms is beneficial to humans.                  
9. Bacteria        
10. Fungi