Stahl Biology

Respiration in Yeast Lab

Name- ______

Class Period-______

Date- ______

Cellular respiration is the chemical process by which cells take in oxygen and glucose (which are the products of photosynthesis) and release carbon dioxide and water (which are the reactants of photosynthesis). Cells accomplish this process by breaking down nutrient rich molecules from the food that organisms eat to generate ATP (Adenosine triphosphate), which is then used to fuel cellular processes that require energy. All cells carry out the process of cellular respiration in order to meet their energy needs for daily survival both day and night.

This processoriginally starts in the cytoplasm via glycolysis, which is an anaerobic process that breaks down the glucose molecules into 2-3 carbon chains, turns them into pyruvic acid (pyruvate), and produces 2 ATP. Remember that pyruvate is actually made naturally in our bodies during metabolism when we digest sugars and starches and is crucial for the Kreb’s Cycle / Citric Acid Cycle to occur and to be successful in cellular respiration. After the breakdown is complete,Coenzyme A bonds to the 2 carbon molecule made from pyruvate and enters the Kreb’s Cycle in the mitochondrial matrix and the process of making high energy molecules continues.

Chemical equation for Cellular Respiration

Yeasts are unicellular microorganisms of Kingdom Fungi. They are a facultative anaerobe, which means that they can respire or ferment depending upon environmental conditions. In the presence of oxygen, respiration takes place (aerobic respiration). Without oxygen present, fermentation occurs (anaerobic respiration). Both processes require sugar to produce cellular energy.

Yeasts use sugar and warm water to grow. The warm water provides heat to the yeast, resulting in an accelerated reaction. As yeast grows it expands and gets bubbly, giving off carbon dioxide, the same gas that your body exhales and plants absorb, and produces ethanol. People use yeast to bake because the carbon dioxide being released forms bubbles in the dough, causing the dough to rise and expand. Since baking is done at high temperatures, yeast ultimately dies and nearly all the ethanol evaporates. Ethanol fermentation is used to produce alcoholic beverages. People also use yeast fermentation to make ethanol for fuel (some information obtained from University of Florida Science Outreach).

Chemical equation for Fermentation

Objective: Students will use the respiration powers of yeast to blow up a balloon. This activity will reinforce the basic principles of respiration as a fundamental metabolic process for living organisms using yeast as a model.

Pre-lab Questions:

  1. Write the chemical equation for cellular respiration and label the products and reactants.
  1. Write the chemical equation for fermentation and label the products and reactants.
  1. In what organelle does cellular respiration take place?
  1. Define aerobic and anaerobic respiration.
  1. What is the function of the mitochondria?
  1. What is the relationship between photosynthesis and cellular respiration?
  1. What is glycolysis and where does it occur in the cell?
  1. How many ATP does glycolysis produce?
  1. What do you think is the importance of Coenzyme A? What is the function of an enzyme?

10. What is a facultative anaerobe? Give an example.

Materials:

1 spoonful of dry yeast

1 Balloon

Warm Water

Recycled water bottle

2 Spoonfuls of Sugar

Masking Tape

Tape Measure

Funnel

Measuring cup

Procedure 1:

  1. Put 1 spoonful of yeast and 2 spoonfuls of sugar in the soda bottle.
  2. Fill the bottle ¾ full of warm water.
  3. Quickly stretch the balloon over the opening of the bottle.
  4. Seal with masking tape.
  5. Shake the bottle to speed up the reaction.
  6. Measure and record the diameter of the balloon every 5 minutes.
  7. Shake as needed to mix the ingredients in between trials.

Procedure 2:

1. Place the bottom of a funnel into the opening of the balloon. You may need to stretch the opening of the balloon a little bit so that it fits.

2. Have a carefully supervised student pour 1 Tbsp. of yeast and 1 tsp. of sugar into the balloon through the funnel. Then fill the measuring cup with warm water from the sink and carefully pour the water into the balloon.

3. Remove the funnel from the opening of the balloon. Tie a knot in the balloon to the water and yeast mixture inside. Measure the diameter of the balloon every five minutes.

4. Record on the data table.

Data Table:

Diameter of Balloon in 5 minute intervals

Time (minutes) / Diameter (cm)
5
10
15
20
25
30
35
40
45
50
55

Data Analysis:

Make a Line Graph representing your data. Remember title & labels.

Post-Lab:

  1. Explain the relationship between time and diameter that you observed.
  1. What was the gas that filled the balloon? Where did it come from? Explain your answer.
  1. What are the reactants in the observed reaction?
  1. What are the products?
  1. What is the purpose of warm water?
  1. Why is respiration important for living organisms?