Biology Planning Exercise
The Uptake of Glucose in Yeast Cells
Glucose is absorbed across the cell surface membrane (plasma membrane) of most cells. A convenient way to investigate this is to use a solution of glucose and a suspension of yeast cells. The amount of glucose taken up from the glucose solution by yeast cells in a fixed length of time can be measured. At the end of the fixed length of time, further uptake of glucose is prevented by transferring the yeast suspension to a boiling water bath to kill the yeast cells. If the suspension is then left to stand, the yeast cells form a sediment at the bottom of the tube. The concentration of glucose that remains in the fluid (supernatant) above the sediment can then be determined. As the original concentration of glucose us known the rate of uptake can be determined.
“High concentrations of glucose will cause a higher rate of uptake in yeast cells”
As the glucose concentration increases, the rate of uptake by the yeast cells will also increase. However, at a certain point, all of the yeast’s active sites will be occupied, so the rate of uptake will even out. This point is known as Vmax.
To test this hypothesis, I will use different concentrations of glucose with a yeast suspension over a set period of time. I will then kill the yeast cells by putting the solution into a boiling water bath, and letting it sink to the bottom as sediment. I can then take a sample of the supernatant from each of the concentrations and perform a Benedict’s test to determine how much glucose is left in the solution. To work out how much glucose has been absorbed by the yeast cells, I will construct a graph by performing the experiment with various concentrations of glucose in preliminary work, and then filtering the product of the Benedict’s test. I can then weigh the filter papers and plot them on a graph. This will allow me to later read off concentrations by using...
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