How to figure generation time

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kaymicro
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How to figure generation time

Post by kaymicro » Thu Oct 08, 2009 3:12 am

So i read generation time is the time it takes for a bacteria to double in number.
This question asks a bacterial cell has a generation time of 40 minutes, how many cells will there be after 5 hours of optimal exponential growth?

i thought it should be 40 * 7 = 280

however, it says the correct answer is 128, i dont understand how thats the answer. Help would be greatly appreciated, thanks.

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JackBean
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Post by JackBean » Thu Oct 08, 2009 5:31 am

Why 40*7? What's supposed to be the 7?

What is the original number? I guess 1 cell? If so, double it every 40 min for 5 hours, that is 1*2^((5*60)/40)
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canalon
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Post by canalon » Thu Oct 08, 2009 3:28 pm

(5*60)/40=7.5
And since we are working with theory, we assume stepwise growth and simultaneous division, so only 7 generations, not 7.5 That is probably where the 7 comes from. The question, is why you would want to multiply it by 40?
AT each generation the number of bacteria is doubling, so you multiply the initial number i of bacteria by 2
so you have i x 2 after the first generation
(i x2) x2 after the 2nd generation which you can simplify to i x2^n after n generations
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jwalin
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Post by jwalin » Thu Nov 12, 2009 3:48 pm

2^7=128
simplified
it isn't what you do that matters but it is how you do it

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JackBean
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Post by JackBean » Thu Nov 12, 2009 4:55 pm

Fine, you gave him a fish right now. Canalon was trying to learn him, how to fish.
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jwalin
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Re: How to figure generation time

Post by jwalin » Sun Nov 15, 2009 3:47 am

i know
:lol: :D :P :lol:
it isn't what you do that matters but it is how you do it

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