Biology-Mr.Willets Lab-Anaerobic Respiration

Most cells respire aerobically. This means that they use oxygen to break apart glucose to release energy. Some cells are able to release energy from glucose without using oxygen. This is called anaerobic respiration Yeast cells can respire anaerobically using alcoholic fermentation as part of the process. Today's lab will examine some of the factors that can affect this process.

When yeast cells respire anaerobically, they produce ethyl alcohol (ethanol) and carbon dioxide. We can measure how fast respiration is occurring by measuring the amount of carbon dioxide produced. To do this, we will use fermentation tubes.

Examine your fermentation tubes. You will see markings on the side. These measure milliliters (ml). The marks for 0.5 ml and 1.0 ml have been darkened with a pen. The top unscrews. You will notice the top has a hole in it. That is supposed to be there. The four tubes should be marked: A , B , C and D. If the markings are not clear, get a wax pencil and redo them.

You will put a mixture of sugar and yeast into the tubes. You will then place them in a beaker of water, cap side down. As carbon dioxide is produced, it will rise to the top of the tube. You can use the markings to measure how much is produced.

The amount of sugar you will use will vary. We will all use hot water in the beaker. Yeast respire better when warm. I will provide you with data from another class where cold water was used in the beaker. We will use class results to draw graphs and make some conclusions.

There are four sugar solutions: A) 0% sugar (plain water) B) 10% sugar C) 20% sugar D) 40% sugar

These sugar solutions (B, C and D) are in flasks on the front desk and on the side bench. For Solution A, just use regular water. The four fermentation tubes are also labeled with those letters.

Procedure-

1) Unscrew the caps from all four tubes. Fill each halfway (to the 8 ml mark) with the appropriate sugar solution. Match the letter on flask with the letter on the tube.

2) Fill a 250 ml beaker with hot water. Use the faucets at the front and back of the room that are running. Do not turn them off.

3) Stir the yeast mixture before using. Fill each tube the rest of the way with the yeast mixture provided to you. The tubes should be filled above the lip of the tube.

4) Add more yeast if necessary to make sure the tube is filled above the lip. Carefully screw the caps on each tube. A little liquid should squirt out the hole in the cap. Turn the tubes a few times to mix. Do not shake them.

5) When all the tubes are ready, place them - cap side down - into the beaker of water. Note what time it is. The beaker should be put into a metal pan to collect the overflow that will occur.

6) Right before you do step #7, fill another beaker with hot water.

7) Wait 4 minutes, remove the tubes - one at a time - read the amount of gas collected at the top. Measure to the nearest 0.5 ml. Any foam counts as part of the gas collected. Record this in Table One. Put the tubes into the new beaker of hot water, cap side down.

8) Repeat Steps #6 and 7 every 2 minutes until you are told to stop.

Table One- All measurements are made in milliliters (ml) of CO2

Temperature in beaker - ________° C

I will collect your data, combine it and average it to form class data. This will be given to you later with instructions on how to analyze it.