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Homework Help: Diffusion rate of oxygen through skin

  1. Sep 14, 2014 #1
    1. The problem statement, all variables and given/known data

    i) At rest a 70 kg person with an area of 1.7 m2 consumes around 14 litres of oxygen per hour. Around 2% of this is provided by diffusion through their skin. Calculate the diffusion rate for oxygen through human skin, in millilitres per second per square metre.
    ii) What is the maximum diameter of a spherical organism whose oxygen requirements may be met entirely by diffusion through skin with the same diffusion rate as the person above? Assume that they have the same density as water and that the oxygen requirement per unit volume is the same as for the person.

    2. Relevant equations

    I have no idea what specific diffusion equation to use for the first part :(

    3. The attempt at a solution

    So I've figured out all of the easy stuff at the beginning. Like he consumes 0.29L of O2 and hour by diffusion and that the mass of one O2 molecule is 5.3x10^-23g but I am totally stumped from here. I've looked through my textbook and found a ton of different diffusion equations such as Flick's law but I can find all of the variables with what I've been given. I have an inkling that I have to use the density of animal fat for something but no luck so far. I was at one point thinking about calculating a concentration value somehow because i saw that in Flick's law but it all comes back to my main problem on me not knowing how to link any of this information together. Am I missing a constant that's well known?

    For the second part I'm positive it is related to SA/V ratio and how smaller organisms = higher ratio values but I'm again stumped on generating a value. Seeing as this 70kg person only takes in 2% of O2 by diffusion I assume that the animal size would be very very small, like insect like?

    Would really appreciate, I'm normally not this hopeless but this question has really confused me.
  2. jcsd
  3. Sep 14, 2014 #2
    Okay so I managed to find the answers online but I would really like to fully understand the question and I still can't seem to figure it out. The answers are 1.71l/hrcm2 and 0.5. I think I'm getting closer to figuring out the second part though.
  4. Sep 14, 2014 #3
    So I'm probably just as lost as you but seeing as the question mentions density for the second part shouldn't you be using the formula of a sphere's volume along with 1g/cm3?
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