HW - 4/25/12

Tonight's homework is to finish Classwork 100 and plan your yeast respiration experiment.

What’s Necessary in your Plan

Your specific question

Your hypotheses

Independent variable(s)

Dependent variable(s)

Control group/Experimental groups

Controlled variables

Data/Observations table

Procedure

You have been hired by ABC Bakery, Inc. to improve their baking recipes so that their bagels and bread are as doughy as their competitors. To do this, you need to develop ways to maximize how much fermentation their baker’s yeast can carry out.

Procedure

The question that you are answering is “How can fermentation by yeast be maximized?”

1. Develop a hypothesis that answers the question. Your hypothesis will be graded based on how clear, specific, and testable it is.

2. Work with your table to design an experiment to test your hypothesis and find out how different variables affect yeast. The materials available are listed below.

thermometer

10 mL graduated cup (for measuring the yeast suspension)

hot plate

ice

water (pH = 7)

acidic solution (pH = 4)

basic solution (pH = 10)

3 test tubes

3 balloons

powdered sugar

stir stick

ruler

BTB – bromthymol blue

clock

Hints:

a.  The yeast needs to be in a mixture called a suspension. It should contain yeast (from a packet), warm water and sugar. Each test tube only needs 10 mL of yeast suspension. If you put a ¼ teaspoon of sugar in 50 mL of warm water (about 40°C or 105°F), then it should be enough for at least three tubes.

b. The more active the yeast, the more carbon dioxide produced. The production of carbon dioxide results in the formation of a layer of foam on top of the yeast solution. The production of carbon dioxide should also produce a color change in the BTB mixture.

c.  Some variables that you should consider are the temperatures that you will use, the amount of sugar you will provide, the pH of the water in the yeast suspension, or the length of time you will allow the yeast to ferment.

d. You measure the amount of fermentation by measuring the amount of carbon dioxide in a few different ways.

3. Write up your hypothesis and experimental plan on Classwork 100B. Make sure it is complete before turning it in or attempting to carry out the experiment.