## How to figure generation time

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

kaymicro
Garter
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### 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.

JackBean
Inland Taipan
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Joined: Mon Sep 14, 2009 7:12 pm
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
Inland Taipan
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(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
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

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

JackBean
Inland Taipan
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Fine, you gave him a fish right now. Canalon was trying to learn him, how to fish.
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

jwalin
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Joined: Tue Sep 15, 2009 3:43 pm