## How to figure generation time

**Moderators:** Leonid, amiradm, BioTeam

### How to figure generation time

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.

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.

(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

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

Patrick

Science has proof without any certainty. Creationists have certainty without

any proof. (Ashley Montague)

Science has proof without any certainty. Creationists have certainty without

any proof. (Ashley Montague)

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