# Help me start please?

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!

## Answers and Replies

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berkeman
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?