Investigating respiration in yeast.

I think early in the range of temperatures I have chosen, the yeast will respire quite slowly but it will increase quite rapidly as the jump in temperatures isn’t by 1 or 2 °C but by 10 °C each time, which biologically for enzymes is a considerably larger leap. At the higher end of the range of temperatures, at one of the temperatures there will be at least a fall in the rate of respiration in the yeast. This is because some of the cells of yeast or nearly all would have denatured due to the high temperature.

I had planned an earlier experiment for this investigation but it lacked in the accuracy of the results and the effect of the addition of extra food to the yeast solution. (The method of measuring the rate of respiration was by counting the number of bubbles escaping from a syringe containing the yeast solution within a temperature-controlled environment; all bubbles would not have been of the same size)

Research: (obtained from a web page on )

“All the ENZYMES are protein chains of amino acids. They exist in the form of ?-helix structure with hydrogen bonds holding the pitches together. On the amino acid molecules, there is R a group. They react with each other to form peptide bonds, transforming the chain into a 3-dimensional structure. Along the chain there are active sites where interaction between the enzyme and the substrate happens. These sites are sensitive to heat, like the hydrogen bonds that hold the 3D molecule together. When heat is applied to the enzyme, energy is given into the molecule. The active sites deform and the hydrogen bonds break, denaturing this enzyme. It would not be able to function as usual, and this is not reversible. This is called DENATURATION. The 3D ?-helix structure would breakdown and the active sites would change in shape; they would not be able to accommodate the substrate any more. The analogy of this is to compare a key to a keyhole. If the keyhole has changed, the same key would not fit in any more, and the lock would not be unlocked. The same thing happens here, and fermentation could not continue after this has occurred. Also when the temperature is too low, the enzymes would not work because there is not enough energy for activities to happen.”

Obtaining Evidence

Apparatus

• Metal tray
• Thermometer
• 2 X 10 cm3 syringes
• Yeast suspension
• Sucrose
• Timer
• Beaker
• Measuring Cylinder
• Test-tube
• Tube
• Bung

Diagram

Method

1. Set up the water bath to 20°C in the beaker.
2. Set up the second water bath with the water at room temperature, any warmer and the air collected may expand, and making it colder will be unnecessary.
3. Fill the measuring cylinder with water and place it upside-down in the collection water bath, with the end of the tube nearly under it, so when the time comes, the air is collected with least delay.
4. Using a syringe, measure 25 cm3 of yeast and insert it into the test tube. This amount is ideal to produce results at this scale (e.g. to avoid all results being below 1 ml and have only slight variations between them)
5. Close the test tube with the bung, place it in the beaker and start the timer.
6. When the timer reaches 1minute place the end of the tube directly under the measuring cylinder. The air that came out before this minute was only the expanded air, and the respiratory products of the yeast that had got to the temperature required, not all of the yeast.
7. Then the timer shows 5 minutes record the quantity of air in the measuring cylinder. This is the best time to stop because of the time limitations to work in, and it provides sufficient results.
8. Repeat steps 1 through 8, and finally record the average of the 2 results.
9. Repeat steps 1 through 9 for 30°C, 40°C, 50°C and 60°C. This is a comfortable range to use as the yeasts more significant reactions are above 20°C and its highly significant drop in results is at about 60°C.
10. Then repeat steps 1 to 9 this time add 5 cm3 of sucrose to the yeast and stir it (at step 4).

Table for Data Collection

Analysing and Processing Evidence

Results

Conclusion

I have found that an increase in temperature causes the yeast to respire faster because, according to my results 25 cm3 of yeast at 20 °C produced no carbon dioxide, but the same amount at 40 °C produced 0.8 cm3 of carbon dioxide and at 60 °C it produced 2.9 cm3 of carbon dioxide. This could be due to the molecules of enzymes in yeast vibrating faster therefore colliding with a food molecule more often.

I have also found that yeast respires a lot more in the same time if given sucrose.

I have found that yeast starts to denature at a certain point between 40 °C and 60 °C (like the enzymes in a human do at a certain temperature) depending on the volume of yeast, the consistency of the temperature and whether it’s consuming sucrose or not.

My prediction was:

“I think early in the range of temperatures I have chosen, the yeast will respire quite slowly but it will increase quite rapidly as the jump in temperatures isn’t by 1 or 2 °C but by 10 °C each time, which biologically for enzymes is a considerably larger leap. At the higher end of the range of temperatures, at one of the temperatures there will be at least a fall in the rate of respiration in the yeast. This is because some of the cells of yeast or nearly all would have denatured due to the high temperature.”

It is very similar to what I have found because there was a rapid change in carbon dioxide produced - “25 cm3 of yeast at 20 °C produced no carbon dioxide, but the same amount at 40 °C produced 0.8 cm3 of carbon dioxide and at 60 °C it produced 2.9 cm3 of carbon dioxide;” and the enzymes in the yeast did denature at a high temperature in the chosen range – “I have found that yeast starts to denature at a certain point between 40 °C and 60 °C (like the enzymes in a human do at a certain temperature)” However I did NOT predict that the volume of yeast, the consistency of the temperature and the addition of sucrose to the solution would effect the point at which the yeast starts to denature.

Evaluating

One of the facts that affected my results was that the temperature of the water bath kept dropping constantly therefore my results weren’t as accurate. Another one was that at the high temperatures the yeast closer to the inside surface of the test tube denatured, and slightly insulted the yeast closer to the centre stopping those yeast cells to denature.

Also, the temperature of the water bath would be more accurately recorded if I had used an electric thermometer to find the temperature of the water bath.

I would also repeat the experiment maybe about 3 or 4 more times if I were to do it again because of the slight difference in the two results from which the average was obtained