Question

1) List 2 advantages of having a capsule. What is one environment where you would find a capsule containing organism? (1.5) 2) List 2 advantages of an endospore. What is one environment where you would find a spore- forming bacteria? (1.5) 3) In Exercise 12, what difference did you observe between the heat treated and non-heat treated soil plating results? (0.5) 1ml 1ml. ImL 1ml iml. Undiluted sample A B C D Colonies on PCA plate 4) A 10-fold serial dilution was performed as shown above. a. What is the volume in the "blank" tubes? (0.5) b. Should you use the plate shown to determine the number of microorganisms in the original sample? Why or why not? Would you do anything differently? (1.5) 5) Is starch agar selective or differential? Is it complex or defined? (0.5)

Answer 1

1. Capsule is present outside the cell wall. It is made of polysaccharide and serves as an additional protective covering.

The capsule provides protection from phages, toxic chemicals, desiccation or drying, action of phagocytes and helps in attachment. Thus the environments include dry environment, harmful chemical environment, temperature fluctuations, extreme heat or cold.

2. Endospores: These are thick walled highly resistant spores produced in response to adverse environment or harmful waste products. During the time of formation of endospores, the protoplast containing nuclear body stores food, undergoes dehydration to form a thick wall around it called endospore.Endospore is metabolically inert, can withstand unsuitable temperature and draught ( conditions). During dry conditions, endospores can withstand temperature of 100 degree celcius for many hours. ( High Temperature).

4. a. Since 1 ml .of liquid is transferred to the next tube, thus the volume in the blank tubes are 1 ml. each.

b. Case 1:If the tubes after the first one contains no other substances but only the solvent or water part, then the number of micro-organisms can be determined in the original sample provided there is homogenous presence of these micro-organisms. If, however, these tubes contain micro-organisms individually, then the number in the original cannot be ascertained..

In case the first one only contains the micro -organisms homogenously, then the number can be easily ascertained as regards the entire dilution which contains the organisms only from the first .

Case 2: there is always a chance of some organisms remaining in the remaining tubes during the dilution process. Thus, the true number of organisms cannot be determined.

In that case a given volume of the contents are taken . micro-organisms are counted, then multiplied with the entire volume to have the total number. Assuming the solution contains the micro-organisms in a homogenous condition.