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1.)The diffusion coefficient for potassium ions crossing a biological membrane 10 nm thick is 1.0 ×

10−16 m2/s. What flow rate of potassium ions would move across an area 100 by 100 nm if the concentration difference across the membrane is 0.50 moles/L

5.0*10^-20 is not the answer


2.) A spherical virus has a radius of 50 nm. What is its expected diffusion coefficient in water at 25 C?



8.72*10^-12  m2/s --> is not the answer


3.) I've been reading Guns, Germs and Steel by Jared Diamond. In it, he estimates that the spread of humans to the Americas, starting from an initial entry point up in Alaska, took around 2000 years to arrive at Tierra del Fuego. He often talks about technology, language,culture and human populations spreading by "diffusion".

Assuming "diffusion" is an accurate model for the spread of humans, what is the effective diffusion coefficient of human hunter-gatherers? You can assume this is essentially a 1D process, since there are bottlenecks along the way (most notably central America) that restrict flow to narrow geographical passages. I took the Alaska - Argentina distance from here; yes, I realize the Pan-American Highway hadn't been built yet in 14000 BC but presumably it's a decent estimate of the total overland distance from upper Alaska to the southern tip of South America.

18.26*10^4 is not the answer

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