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Diffusion and slime molds

Page history last edited by Joe Redish 9 years, 8 months ago

4.3.3.P4

 

When starving for nutrients, individual slime mold cells get together to form spores, which are effectively colonies with thousands of cells. The way the slime mold cells find each other is by detecting the presence of a tracer chemical that each cell emits, and essentially moving against the flow of tracer chemicals.  Each cell emits the tracer chemical from one end (the “tail”) and detects it at the other (the “head”).  In the figure at the right is shown a picture of 5 cells (labeled A through E) on a contour map of the concentration of the tracer chemical. The white dot on each cell is the head, where the flow of the chemical is detected. The amount of concentration of the tracer chemical is shown by a color code with red being the strongest concentration, then orange, then yellow, then blue, with dark blue being the lowest concentration.

A. Consider one of the cells, labeled “A”, which detects a flow of the tracer chemical. In what direction are the molecules of the tracer chemical detected by A preferentially moving? (Use the coordinate system shown to specify your direction.) Explain why you think so.

 

B. What is there about the distribution of tracer chemical that results in a flow in a single direction that the cell can sense? Don’t the molecules of the tracer chemical move in all directions equally? Explain.

 

C. Cells B, C, and D are emitting tracer chemical, but it doesn’t seem to have reached cell E yet. What would you need to know in order to estimate the time it would take the tracer chemical emitted from B, C, and D to diffuse to the location of E and how might you estimate that time?

 

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