EK Biology Test #3 Question??

[ilovemedi]

I'm not sure why #49 and #50 is hard for me to understand.

#49 Question: If regulations require canned food to be heated to 121deg to reduce a colony of C. boutlinum in a phospahte buffer from 10^12 bacteria to 1 bacterium, how long must the canned food be heated for?
Answer is B. I'm confused... if we reduce from 10^12 to 10, we are dividing by 10 12 times. Why does that translate to multiplying "D" by 12 times (which is time required to kill 90% of microorganism)? Also going from 10^12 to 10 is basically a 99% decrease... so not sure how it applies?


#50 - Answer is C. I thought it was B, because that's how log graphs look like. Does this question ask what does only a section of a log scale (the "increasing part") look like? Which is a straight line???

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[DrknoSDN]

#49 - I missed that also. You probably didn't see that the D value (90% 'half-life') is 0.2 minutes so 12 D Values at 0.2 minutes. is 2.4 minutes.
Also a single D value will take the colony size from X to X/10 or only 10 percent previous level. So this problem is dealing with pseudo half-lives. After 2 D values you have 1/100 or 1%, and have 3 you have 0.1% After 12 d values you have 1/10^12.

#50 - I think it's asking for more of a general image. If you have a colony growing exponentially (say 10x previous size every hour), on a log scale it would appear linear (would go up by 1 every hour). Remember they are only taking the log of the cells so the time axis is normal. If you log both axis you would get a graph like B, I think.

 

[ilovemedi]

#49 - I missed that also. You probably didn't see that the D value (90% 'half-life') is 0.2 minutes so 12 D Values at 0.2 minutes. is 2.4 minutes.
Also a single D value will take the colony size from X to X/10 or only 10 percent previous level. So this problem is dealing with pseudo half-lives. After 2 D values you have 1/100 or 1%, and have 3 you have 0.1% After 12 d values you have 1/10^12.

#50 - I think it's asking for more of a general image. If you have a colony growing exponentially (say 10x previous size every hour), on a log scale it would appear linear (would go up by 1 every hour). Remember they are only taking the log of the cells so the time axis is normal. If you log both axis you would get a graph like B, I think.

FOR #49, WOW, I would never have thought to do it that way. I'm going to be screwed for the tests. It makes sense, yes, but I would've gotten that wrong. So D value is basically (Xpopulation initial)/10=Xfinalpopulation .. and each division by 10 is another d value ... which in this case takes 12D values to go from 10^12 to 1..

Same w/ #50.. i think that would've been hard for me to figure out if I hadn't take a stats class... gahhh. well, THANK YOU for your help!!

 

[DrknoSDN]

FOR #49, WOW, I would never have thought to do it that way. I'm going to be screwed for the tests. It makes sense, yes, but I would've gotten that wrong. So D value is basically (Xpopulation initial)/10=Xfinalpopulation .. and each division by 10 is another d value ... which in this case takes 12D values to go from 10^12 to 1..

Same w/ #50.. i think that would've been hard for me to figure out if I hadn't take a stats class... gahhh. well, THANK YOU for your help!!

Don't worry about it too much, i missed 49 when i did it. Honestly you get a lot of questions wrong studying. The reason it's so important to do so many practice problems is because when you see a similar one on the exam, you know how to answer it. Practice practice practice.