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Unformatted text preview: ENCH 468N/648N; BIOE 689N: H OMEWORK A SSIGNMENT 1 Topic: BioNano World: Physical, Chemical Aspects Assigned: Sept. 16, 2008; Due: Sept. 30, 2008 1. Diffusive Intake of Food by a Bacterial Cell : In class, we discussed the intake of food by a spherical bacterial cell of radius R . Assume that the cell is in a pool of fluid that contains food at a concentration of C (mol/L). Also, assume that, as soon as the food reaches the cell surface, the food is taken in by the cell. (a) Under these conditions, DERIVE an expression for the food concentration profile C ( r ), where r is the distance from the center of the cell. Use Ficks law and use appropriate boundary conditions for the problem. (b) DERIVE an expression for the rate of food intake I by the cell. Note that I will have units of (mol/s). 2. Distance a Swimming Bacterial Cell Can Coast : In class we discussed that a bacterial cell swims by rotating its flagellum. As long as the cell rotates the flagellum, it will keep swimming. The question now is: what happens when it stops this rotation will the cell be able to coast before it comes to a stop? Recall that, when we swim, we can coast for significant distances, depending on our initial speed....
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- Spring '08