Question

a. I) explain the difference between mesophilic and thermophilic micrograms ii) what relevance are these two different to composting? Iii? How does composting control pathogens? b. I? using a labelled diagram describe the four stages seen in bacterial growth curves ii) list 4 environmental factors that influence the curve

Answer 1

a) i) DIFFERENCE BETWEEN MESOPHILIC AND THERMOPHILIC MICROORGANISM:-
MESOPHILES:-
-Live in moderate temperature ranges 20° -45°C.
-Optimum temperature is 37° C.
- live in cheese, yoghurt,beer,wine ,human intestine etc.
- cell components are less stable than thermophile.
- Examples - staphylococcus aureus, E. Coli.

THERMOPHILE:-
- live in relatively high temperature ranges from 45°-80° C.
- Optimum temperature is 50°C.
- exposrled to direct sunlight, deep thermal event etc.
- cell components are more stable than mesophile.
- Example- Thermus aquaticus.

(ii) RELEVANCE TO COMPOSTING:-
- Composting is a process in which micro-organisms break down organic matter and produce carbon dioxide, water, heat, and humus(the relatively stable organic end product).
- composting has three phases:-
1) mesophilic- by mesophiles
2)thermophilic- by thermophile
3)maturation phase.

(iii) composting controlling pathogens:-
- Initially decomposition occurred by mesophilic microorganisms, which break down the soluble, degradable compounds.
- The heat produced causes eise in Temperature.
- When temperature becomes above about 40°C, the mesophilic are replaced thermophilic.
- As raw material of these compounds becomes exhausted, the compost temperature decreases and mesophilic microorganisms once again take over for maturation phase.

(b) BACTERIAL GROWTH CURVE:-

four phases are as below-
1) Lag phase- no increase in number of living cell.
2) Log phase:- exponential Increase in number of living bacterial cells.
3) stationary phase:- plateau in number of living bacterial cells.
- rate of cell division and death is equal.
4) decline phase- exponential decrease in number of living bacterial cells.

(ii) Environmental factors influencing curve:-
1. solutes and water activity
2. pH
3. temperature
4. oxygen concentration