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Homework Help: Help me start please?

  1. Feb 13, 2007 #1
    Within a monolayer phospholipid molecules exchange places with their neighbors every 10^-7 seconds. It takes about 1 second for a phospholipid to diffuse from one end of the bacterium to the other, a distance of about 2 micrometers.

    A) Are these numbers in agreement? Assume that the diameter of a phospholipid head is 0.5 nm. Explain why or why not.

    B) To gain an appreciation for the speed of molecular motions, assume that a lipid molecule is the size of a ping pong ball (4 cm diameter) and that the floor of your living room (6 m by 6 m) is covered wall to wall in a monolayer of balls. If two neighboring balls exchanged positions every 10^-7 seconds how fast would they be moving in km/h? How long would it take for a ball to move from one end of the room to another?

    I am not sure where to begin with these and what type of equations to use. If anyone can at least help me begin thatd be greatly appreciated!
  2. jcsd
  3. Feb 13, 2007 #2


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    Staff: Mentor

    Well at least part B is straightforward algebra. A ping-pong ball moves 4cm every 0.1us. What is that velocity in units of km/hr? At that speed, how long does it take for a ball to travel the 6m to go from wall-to-wall?

    Then I guess you're supposed to use a similar analysis to check the numbers for the biological dimension case in part A. Does that help?
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