Here are the notes I made for an experiment I was doing (I didn't put it here as it is too long)

(please ignore the numbers at the end of the pdf file)

The graph looks like this:

enter image description here

As you see on the graph, the numbers are the same as the ones below

1. The effect running out of glucose has on the yeast growth Our yeast increased in number by dividing rapidly. They use glucose to respire and release energy. They need energy to grow.

2. Why the yeast starts to grow again The yeast starts to decrease in volume when they ran out of glucose.

3. Describing patterns in graphs The yeast breaks down the starch to glucose

The problem is, why did the yeast rise at the end, I forgot?

Thanks in advance

  • $\begingroup$ I just would like to say that the teacher never talked about the production of Co2 $\endgroup$
    – Turbo
    Nov 3 '13 at 20:36
  • $\begingroup$ What did your growth medium contain? Only glucose? Or other substances as well? $\endgroup$
    – Chris
    Dec 8 '14 at 22:04
  • $\begingroup$ @Chris only glucose $\endgroup$
    – Turbo
    Dec 9 '14 at 20:30
  • $\begingroup$ So you added glucose and some salts into the medium? Or did it also contain some complex materials like yeast or tryptone extract? $\endgroup$
    – Chris
    Dec 9 '14 at 20:31
  • $\begingroup$ What do you mean by Volume. Volume occupied by yeasts? Then it is not the cell number. $\endgroup$
    – 243
    Dec 8 '15 at 18:48

First, the glucose is reduced by anaerobic fermentation to ethanol and carbon dioxide. The yeast uses the produced energy for a fast growth and division (1). As soon as all glucose is consumed the metabolism of the yeast changes from anerobic fermentation to aerobic respiration (oxygen is required). This is called diauxic shift. During this time the yeast stops growing (2). After this shift the yeast further reduces the ethanol to carbon dioxide and water. The generated energy is used for the second growth phase (3). Hope this answers your question. Best Vanessa

  • $\begingroup$ Ethanol is toxic for yeast, it cannot metabolize the large amounts produced during fermentation. This is the reason why most wines are not stronger than 12-14% alcohol. $\endgroup$
    – Chris
    Dec 8 '15 at 19:45
  • $\begingroup$ Welcome to Bio. Some references would be appreciated. $\endgroup$
    – AliceD
    Dec 8 '15 at 20:28

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