Question

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1. What is the relationship between the sizes of the agar blocks and the rate of diffusion (mm/min)?

2. What factors can affect the rate of diffusion (mm/min) in living cells?

3. Why are the cells of most eukaryotes about the same size?

4. What is the relevance of surface area to living cells?

Answer 1

1. When the cell increases in size, the volume increases faster than the surface area, because volume is cubed where surface area is squared. When there is more volume and less surface area, diffusion takes longer time and is less effective.

2.The rate of diffusion of solvent is affected by the concentration gradient, membrane permeability, temperature, and pressure. Diffusion takes place as long as there is a difference between the concentrations of a substance across a barrier.

Several factors affect the rate of diffusion of a solute including the mass of the solute, the temperature of the environment, the solvent density, and the distance traveled.

3.A typical eukaryotic cell is about 10 µm – 20 µm. This range is so small that it seems like most of the eukaryotes have same size.

4.The important point is that the surface area to the volume ratio gets smaller as the cell gets larger. Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased cellular volume. That is why cells are so small.