Question

1. place flask in warm water bath and start a timer for 30 minutes. continue measuring the circumference every 5 minutes for remaining 25 minutes. also record qualitative observations.

***most groups will start with step 6!!!***

1. in a 125 ml flask, dissolve a predetermined amount of sugar in 100 ml of warm tap water. use the amount of sugar chosen by your group. swirl in the flask until it dissolves.
2. add about 3 grams of yeast to the flask. swirl the flask to mix the yeast into the solution.
3. stretch the neck of a balloon a few times. attach the stretched balloon over the top of the flask.
4. measure the circumference of the balloon initially. record the measurement in the data table.
5. place flask in warm water bath and start a timer for 30 minutes. record qualitative data as time progresses.
6. using the measuring tape, measure the circumference of the balloon in cm after 5 minutes then measure the circumference every 5 minutes for the remaining 25 minutes. record your data.
7. add your data to the class spreadsheet.
8. when time is up, place the flask into the sink. when removing the balloon, pull the neck of the balloon away from the next of the flask to release the built up air and fluids within the balloon.
9. throw away the balloon. wash the flasks in the flask down the drain.
10. clean up all materials. place clean lab equipment on lab table as it was found.

learning target: i can investigate and categorize what substance(s) is produced during yeast fermentation and what substance(s) is required for yeast fermentation.
pre - lab
research question: what do you want to know?
how does the amount of sugar provided to the yeast affect the rate of respiration?
independent variable: what experimental factor will you change to produce an outcome?
dependent variable: what will you measure? will you collect quantitative data or qualitative data?
control group: what kind of control group will you establish as a standard for comparison?

Explanation:

• Independent variable: The amount of sugar provided to the yeast. This is what the experimenters will change to observe its effect on the outcome (rate of respiration).
• Dependent variable: The rate of respiration. This will be measured by the circumference of the balloon (quantitative data). As yeast ferments (a form of respiration in the absence of oxygen), it produces carbon dioxide gas which inflates the balloon. The circumference of the balloon over time gives an indication of the rate of gas production (rate of respiration).
• Control group: A group with no sugar added. This serves as a standard for comparison. Without sugar (a key substance for fermentation), yeast would not be able to carry out fermentation (or would do so at a negligible rate), allowing researchers to see the effect of sugar by comparing to this control.

Answer:

• Independent variable: Amount of sugar.
• Dependent variable: Rate of respiration (measured by balloon circumference - quantitative data).
• Control group: Flask with yeast but no sugar added.