Dear Sadhana,

the correct answers are:

Q.21 c

Q22 a

To solve this you need to linearize your data, because destruction of microorganisms usually follows logarithmic order. You will get two points, on which you can calculate linear trend line.

It should be: y=-0,6591x+3,9602 where y is log of survivals and x time in minutes.

Then you should calculate the time needed for 90% reduction of microorganim number (1 logarithmic unit). From one of previous logarithmic values substract 1 and calculate the time. The difference between time of this two points is D-value.

The second part is easier. You want to kill 99,999% of bacteria (5 log units), so you need to multiply D-value by 5.

If you have further questions please ask.

Pawel

Sir also why this 99.999% is considered as 5 log units?

Lets assume that you have 100000 of bacteria and you want to kill 99.999% (that gives only one bacteria that survives).

After first reduction you will kill 90% (10000 survives), second reduction will kill 90% of this 10000 ( 1000 survives) and so on.

So

1st redution time - 90% is killed

2nd - 99%

3rd - 99.9%

4th - 99.99%

5th - 99.999%

I completely understood now. Thank You Sir. I learnt so much.