Limiting Factors and Population Growth Yeast Lab Experiment

Introduction Why Study Yeast Populations? • Yeast is a good model organism because it is simple, but has many of the same processes as more complicated cells. • Yeast use simple sugars to perform cellular respiration and make ATP. During cellular respiration, they release CO 2 as a waste product, just like animals and plants. [sugar + O 2 CO 2 + H 2 O + ATP (energy)] • Since more yeast cells will release more CO 2, we can use the amount (or volume) of CO 2 volume as a measurement of the amount of yeast cells. The amount of yeast cells will tell us the size of the population. [Amount of CO 2 ~ Population Size] DID YOU KNOW? Yeast population variations produce flavor characteristics in a wide variety of food products such wine, beer, and bread.

Use of Energy, Growth and Reproduction in Yeast The yeast cells undergo cellular respiration! As they grow, more cells make more CO 2! Yeast Cell A D D SU G AR Cell Division Occurs S U G A R The process repeats producing more yeast cells and even more CO 2 gas as more cells make more gas

Your Task • Determine how environmental conditions such as food availability, p. H, temperature, light, etc. can effect the growth of a yeast population • REMEMBER: we can use CO 2 (carbon dioxide) volume as a measurement of the size of the yeast population in the test tube.

Measuring Yeast Population Growth by CO 2 Production STEP TWO: Add 1 ml of yeast mixed in water (Yeast Suspension) STEP ONE: Fill a small test tube with 30 ml of a 0, 1 or 2% Molasses solution. STEP THREE: Mix the yeast in the solution by putting the clean palm of your hand over the end and inverting it 5 times

CO 2 Collection Set-up Resulting Air Bubble Large Test Tube Small Test Tube inverted and filled w/ yeast molasses solution STEP FOUR: This is the double test tube set up for collection of CO 2. To obtain this the lager test tube is placed over top of the smaller filled test tube. It is then quickly inverted so that the larger test tube is open and the smaller one is upside down. An air bubble will be left at the top of the tube.

Collecting Data 5 mm 11 mm 30 mm Day 1 Day 3 Time in DAYS Day 5 Students Collect CO 2 Bubble Height Data for 5 Days

Data: CO 2 Bubble Height (mm) from: Yeast Grown in Various Concentrations of Molasses (0%, 1%, 2%) OR Yeast Grown in 1% Molasses Solution at Various Temperatures (Cold, Room temperature, Warm) DAY ONE TUBE 1 0. 0 2 0. 0 3 0. 1 4 0. 1 5 1 6 1 Bubble Height measured in mm. DAY TWO DAY THREE

Definitions Problem Statement: The problem that the scientist is trying to solve. Hypothesis: An educated guess that answers the problem statement. Often, an “If… Then…” statement is used. So, If I change the independent variable, Then the dependent variable will change in this way. Independent Variable: The variable in an experiment that the scientist purposefully changes. This change should affect the dependent variable. Dependent Variable: The variable in an experiment that changes and that the scientist measures. This variable depends on the independent variable. Control: The “baseline” that you can compare the other groups exposed to the independent variable against. Used test how valid the independent variable is. Controlled Experiment: An experiment in which all factors are kept constant except for the independent variable. 9