Understanding Anaerobic Respiration in Yeast Fermentation Lab, Summaries of Chemistry

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Patrick Baqué, Laurent Hekayem,·

Bread-Baking Lab:

Teacher’s Guide

Bread-Baking Lab: Teacher’s Guide

BACKGROUND KNOWLEDGE

These lessons are intended to follow instruction on cellular respiration, where students understand the differences between aerobic and anaerobic respiration. Anaerobic respiration includes alcoholic fermentation or lactic acid fermentation. The bread-making lab takes advantage of alcoholic fermentation by yeast. Yeast can undergo aerobic or anaerobic respiration. In bread-making, the yeast starts off respiring aerobically, producing water and also carbon dioxide to make the dough rise. When the air runs out, the yeast begins to respire anaerobically. Any alcohol produced boils away during baking. Most of my students had never made bread before, so this was a fun adventure. In addition to being an activity to drive home cellular respiration content, I also hope they learned something new that might transfer to them being able to try something new in their kitchen at home. Despite using the same recipe, the resulting products did vary, and it really just added to the fun for us. They were excited and the other classes were jealous. ☺ LESSON 1: Pre-Lab Day and Cellular Respiration Review During this lesson, students should complete the Cellular Respiration Review Concept Map. When students finish, talk through the main ideas and highlight the pathway of alcoholic fermentation. Then introduce the lab, distribute the recipe and watch the video to expose students to the recipe and process. Discuss the role of carbon dioxide in making bread rise, and that the small amount of alcohol is removed during baking. LESSON 2: Lab Day 1 In this lesson, students will mix and knead the dough and leave it to rise. Prior to the lab, clean students’ work surfaces with sanitizing cleaner and have students wash their hands. Following Day 1, allow the bread to rise for about two hours after class ends. Then put the bowls of dough into a refrigerator overnight. Remove them promptly the next morning so that the dough will warm again, to at least room temperature, before class begins. LESSON 3: Lab Day 2 Have students wash their hands. In this portion of the lab, students will shape the dough into a loaf and then leave it to rise. Following Day 2, you will need to determine when you would like to bake the bread. It could be baked after rising for 30 minutes to an hour, and then could be served cool the following day. Or it could be stored in the refrigerator overnight, allowed to warm up the next morning, and then baked. LESSON 4: Serving the Bread and Cellular Respiration Review Bring butter and/or jam to serve with the bread. If you have time, a tasty option to make is brown sugar-cinnamon butter (just blend ½ cup butter, ¼ cup brown sugar, and ¼ tsp cinnamon). You might consider peanut butter, but be aware of potential student allergies.

Lab Preparation:

Materials needed per group Sample Calculations based on 6 groups and Notes/Tips Large mixing bowl • 6 large mixing bowls

• I purchased large plastic bowls at the dollar store Measuring cups and spoons 1 tbsp, 1 tsp, ½ cup, ¾ cup, 1 cup
• Groups can share these, but 2 or 3 sets are needed to keep things moving.
• I recommend setting out measurement cups/spoons that stay with each ingredient, not with each group Whisk • 6 whisks ½ cup warm water • 3 cups warm water
• I warmed water in the microwave right before class and put it in a pitcher. I used plastic drink cups to hold the water-yeast mixture 2 ¼ tsp yeast (1 packet) • 6 yeast packets
• you could buy 6 individual packets or a 4 oz jar, which would be much more than enough 2 tbsp + 1 tsp sugar • 1 cup of sugar is just enough for 6 groups
• 1 cup = 16 tbsp
• you could bring from home, or buying 1 4lb bag will be much more than enough ¾ cup milk • 4 ½ cups of milk
• ½ gal = 8 cups
• I warmed milk in the staff microwave right before class and put it in a pitcher. 2 tbsp butter • 12 tbsp
• 2 sticks will provide 16 tbsp (1 stick = 8 tbsp)
• Be sure the butter has been left out of the refrigerator to soften. 3 cups flour • 18 cups
• Probably buy two bags of flour, as a 5lb bag is about 16 cups Proofing oven (^) • In a classroom, you may have to get a bit creative to create a warmer environment and expedite rising. I had students put their bowls to rise on my plant stand after the first day and attached heat lamps to it – which worked great. Loaf pan • 6 loaf pans
• I was able to buy cheap ones for about a dollar at Wal- Mart and re-use them year to year. Disposable foil ones are another option. Plastic wrap • The class can use one roll Vegetable oil • Each group needs just a tablespoon or so to coat their bowls, so they can share from one bottle Plates or napkins, plastic knives, butter/jam, bread slicing knives, etc.
• For serving and eating the bread. ☺

Basic White Bread Recipe

(Hand kneading method) video: http://redstaryeast.com/yeast-baking-lessons/how-bake-videos/

• ½ cup warm water (110º to 115ºF / 43 to 46ºC)
• 2 ¼ teaspoons yeast (1 packet)
• 1 teaspoon granulated sugar
• ¾ cup milk
  • 2 tablespoons granulated sugar
  • 2 tablespoons butter
  • 1 teaspoon salt
  • 2 ¾ to 3 cups bread flour

1. Measure the water and put into a cup for ‘waking’ the yeast. Add the yeast and 1 teaspoon granulated sugar; stir briefly until dissolved. Let rest for 10 minutes. (The mixture will begin to foam and fill the cup. If this is not happening, start over with water, yeast and sugar.)
2. Meanwhile, measure and warm the milk by microwaving for 30 seconds or until milk is warm (80ºF/27ºC).
3. In large bowl, add the milk, 2 tablespoons sugar, butter and salt. Whisk to combine.
4. To the bowl, add 1½ cups of the flour, whisk or stir until smooth.
5. Add dissolved yeast mixture; whisk or stir until smooth.
6. Add remaining flour, 1 cup at a time, stir until combined. Add just enough of the remaining flour until the mixture begins to form a ball. Turn out onto a floured surface or board.
7. Add just enough additional flour to keep it from sticking to the board and to your hands. Knead 8 to 10 minutes (set the timer).
8. While kneading, have someone rinse out your group’s bowl and wash the whisks, measuring cups, etc.
9. When dough is elastic and smooth, place in a large bowl that has been lightly coated with butter or oil. Turn once to coat the top of the dough. Cover bowl with plastic wrap. Place in a warm place to rise until dough tests ripe or is about doubled in size.
10. Clean your work surface.

• • Stop Day 1 - - - - Your teacher will put the dough in the refrigerator overnight after it has risen. - -

11. Punch down; let rest 10 minutes.
12. Meanwhile, lightly grease a loaf pan (approx. 9x5-inch).
13. Roll dough into a 7x9-inch rectangle. Beginning on the 7-inch side, roll up tightly and place in loaf pan. Cover and let rise again until nearly double in size (about 30 minutes).

• • Stop Day 2 - - - - Bread will be baked before next class- -

Cellular Respiration Lab (AKA The Bread Lab)

Background Information: Yeast are tiny single-celled fungi. The organisms in the Kingdom Fungi are not capable of making their own food. Fungi, like any other organism, need food for energy. They rely on sugar found in their environment to provide them with this energy so that they can grow and reproduce. Yeast, like bacteria grow in or on their food source. They produce and release digestive proteins (enzymes) into their environment where the sugar molecules are found. Sugar molecules then break down into smaller molecules that can be absorbed by the yeast and used for food (energy). Yeast is a facultative anaerobe, meaning that it can participate in aerobic respiration when possible, but when it is not, it respires anaerobically. When using yeast in making dough, the yeast will use the initial oxygen up very quickly, and then start to undergo anaerobic respiration. There are many species of yeast, and each has a particular food source.

• Certain yeast feed on a variety of natural sources of sugar such as fruits, nectar from plants, and molasses from the plant crop called sorghum.
• Others break down wood and corn stalks. In doing this, a compound called ethanol is produced. This compound can be used in our cars like gasoline.
• Another species break down sugar from grain into alcohol. Others break down fruits into wine, which is another type of alcohol.
• Bread recipes rely on yeast to break down sugar in our dough. All of these processes are called fermentation. Overall, the final equation for glycolysis plus alcoholic fermentation is: C 6 H 12 O 6 = 2CH 3 CH 2 OH + 2CO 2 + 2 ATP glucose = ethyl alcohol + carbon dioxide + energy For the yeast cell, this chemical reaction is necessary to produce the energy for life. The alcohol and the carbon dioxide are waste products produced by the yeast. It is these waste products that we take advantage of. CO 2 creates gas bubbles causing bread to rise. Gluten is a wheat protein that allows bread to stretch when rising. The heat from baking kills the yeast and also evaporates the alcohol.

1. Are yeast autotrophs and heterotrophs? Identify which one they are, and then explain why.
2. Most recipes for bread have you add a small amount of sugar or molasses to the mixture. What purpose does the sugar serve?
3. Distinguish between obligate and facultative anaerobes.
4. What are the two products, besides energy for the yeast, that are produced by yeast undergoing alcoholic fermentation?
5. What happens to the small amount of alcohol produced as the bread is made?
6. What happens to the yeast during the baking?

Name: Date: Period:

Cellular Respiration

begins with which is broken down during produces a net gain of occurs in the which produces can be used in anaerobic respiration such as in produces a total of can be used in which requires aerobic respiration such as in starting with produces a net gain of occurs in the followed by occurs in the which produces which produces produces a net gain of 2 ATP 2 ATP 32 ATP 36 ATP alcoholic fermentation carbon dioxide (CO 2 ) cytosol electron transport ethanol glucose glycolysis Kreb’s cycle lactic acid lactic acid fermentation mitochondria oxygen pyruvates

1. ATP used for cellular energy is a high-energy nucleotide with three phosphate groups. Color this diagram of ATP and label the component parts.
2. Cellular respiration is the process by which molecules are broken down to produce energy in the form of , which is used for most cellular processes.
3. Write the chemical formula for glucose.
4. What are the two types of cellular respiration?
5. Write the balanced chemical equation for aerobic cellular respiration.
6. How many ATP molecules does anaerobic respiration produce from each glucose?
7. How many ATP molecules does aerobic respiration produce from each glucose?
8. What are the three stages of aerobic respiration?
9. List two ways that alcoholic fermentation is used in the food/beverage industry.
10. Describe which type of cellular respiration our bodies normally do, and then describe when our cells sometimes use a different type of cellular respiration.

ANSWERS

Cellular Respiration Lab (AKA The Bread Lab)

Background Information: Yeast are tiny single-celled fungi. The organisms in the Kingdom Fungi are not capable of making their own food. Fungi, like any other organism, need food for energy. They rely on sugar found in their environment to provide them with this energy so that they can grow and reproduce. Yeast, like bacteria grow in or on their food source. They produce and release digestive proteins (enzymes) into their environment where the sugar molecules are found. Sugar molecules then break down into smaller molecules that can be absorbed by the yeast and used for food (energy). Yeast is a facultative anaerobe, meaning that it can participate in aerobic respiration when possible, but when it is not, it respires anaerobically. When using yeast in making dough, the yeast will use the initial oxygen up very quickly, and then start to undergo anaerobic respiration. There are many species of yeast, and each has a particular food source.

• Certain yeast feed on a variety of natural sources of sugar such as fruits, nectar from plants, and molasses from the plant crop called sorghum.
• Others break down wood and corn stalks. In doing this, a compound called ethanol is produced. This compound can be used in our cars like gasoline.
• Another species break down sugar from grain into alcohol. Others break down fruits into wine, which is another type of alcohol.
• Bread recipes rely on yeast to break down sugar in our dough. All of these processes are called fermentation. Overall, the final equation for glycolysis plus alcoholic fermentation is: C 6 H 12 O 6 = 2CH 3 CH 2 OH + 2CO 2 + 2 ATP glucose = ethyl alcohol + carbon dioxide + energy For the yeast cell, this chemical reaction is necessary to produce the energy for life. The alcohol and the carbon dioxide are waste products produced by the yeast. It is these waste products that we take advantage of. CO 2 creates gas bubbles causing bread to rise. Gluten is a wheat protein that allows bread to stretch when rising. The heat from baking kills the yeast and also evaporates the alcohol.

1. Are yeast autotrophs and heterotrophs? Identify which one they are, and then explain why. Heterotrophs – not capable of making their own food/sugar for energy
2. Most recipes for bread have you add a small amount of sugar or molasses to the mixture. What purpose does the sugar serve? Food source for the yeast
3. Distinguish between obligate and facultative anaerobes. Obligate anaerobes cannot live with oxygen. Facultative can utilize both pathways.
4. What are the two products, besides energy for the yeast, that are produced by yeast undergoing alcoholic fermentation? Carbon dioxide and alcohol
5. What happens to the small amount of alcohol produced as the bread is made? Mostly bakes off / evaporates
6. What happens to the yeast during the baking? They are killed by the high temperatures. You are yeast murderers.

ANSWERS

Cellular Respiration

begins with

glucose

which is broken down during produces^ a net gain of

2 ATP

glycolysis occurs

in the cytosol

which produces

36 ATP

pyruvate

produces a total of can be used in anaerobic respiration such as in can be used in aerobic respiration which requires

oxygen

2 ATP

such as in starting with produces a net gain of

alcoholic lactic acid

occurs in the

mitochondria

Krebs cycle

followed by occurs

fermentation fermentation

in the

electron transport

which produces which produces produces a net gain of

32 ATP

2 ATP 2 ATP 32 ATP 36 ATP alcoholic fermentation carbon dioxide (CO 2 ) cytosol electron transport ethanol glucose glycolysis Krebs cycle lactic acid lactic acid fermentation mitochondria oxygen pyruvates

1. ATP used for cellular energy is a high-energy nucleotide with three phosphate groups. Color this diagram of ATP and label the component parts.
2. Cellular respiration is the process by which glucose molecules are broken down to produce energy in the form of ATP , which is used for most cellular processes.
3. Write^ the^ chemical^ formula^ for^ glucose.^ C 6 H 12 O 6
4. What are the two types of cellular respiration? aerobic and anaerobic
5. Write the balanced chemical equation for aerobic cellular respiration. C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O + energy
6. How many ATP molecules does anaerobic respiration produce from each glucose? 2
7. How many ATP molecules does aerobic respiration produce from each glucose? up to 36
8. What are the three stages of aerobic respiration?
   1. glycolysis
   2. Krebs cycle (citric acid cycle)
   3. electron transport (oxidative phosphorylation)
9. List two ways that alcoholic fermentation is used in the food/beverage industry. Ex. bread/baking, beer/wine, swiss cheese
10. Describe which type of cellular respiration our bodies normally do, and then describe when our cells sometimes use a different type of cellular respiration. Human cells generally use aerobic respiration. Muscle cells have the capability to perform some lactic acid fermentation under strenuous exercise conditions.