Yeasty Beasties

Objective

Basic introduction to the idea that all creatures are made up of cells. Introduce basic cell biology of bacteria (prokaryotes) and plant, animal and yeast cells (eukaryotes). Discuss where yeast comes from and what it looks like. Have students learn to measure flour correctly for recipes. Make Amish Friendship Bread starter in a Ziplock bag and observe over the week in the classroom.

CA Standards--Second Grade

• 2.1 History--How things happened long ago, past and now
• 2.4 Food Production/Consumption from long ago; preservation of food

CA Standards--Third Grade

• Structures of Life Module--Foss

Materials

The iCell app on the iPad was useful for illustrating the difference between animal and plant cells. Unfortunately, the program does not include yeast cells. I used pictures printed off the internet (see below).

• Measuring cups and spoons, at least one clear bowl or measuring cup
• Ingredients: Rapid Rise Yeast packet (1 packet per Ziplock bag of Friendship bread), plus one for demonstration purposes
• Sugar
• Flour for the recipe and flour in a large bowl to practice measuring, spoon, and a straight edged instrument like a butter knife.
• Milk
• Wooden Spoon
• Non-metal bowl

Procedures

• Place several cups of flour into a large bowl prior to instruction for use later in measuring step.
• Start by leading a discussion about living things and the structures of life. Ask what do animals need to survive. Students will respond with answers like eat food, drink water, sleep, produce waste, and reproduce.
  • Ask if they know structures for how an organism reproduces itself.
    • Baby
    • Seed
  • And something they probably didn’t think about: Bud or Spore. Show a picture of yeast sporulation and explain that a little piece splits out and becomes a new yeast. We will focus on yeast.
• Explain that all living things are made up of cells which are the smallest building blocks of life. The iPad app can be used to show the difference between plant and animals cells. Plant cells are rectangular shaped, have rigid cell walls and chloroplasts. Explain that yeast or fungi have characteristics of both plant and animals cells. There are two different types of cell types:
  • Prokaryotes have a simpler cell structure and are recognized as bacteria.
  • Eukaryotes which are made up of plants, animals and yeast.
    • Take time to explain that yeast are in the same family as funguses (things like mold and mushrooms).

Yeast

• Ask where do we find yeast in our lives. Kids may suggest: bread, beer, wine, root beer
• Mention that yeast do all the things that animals do and remind them that waste production should have been included at the very beginning.
  • What kind of waste do we produce when we breathe out? Answer: CO2.
  • Yeast eat sugar and then produce CO2 as waste.
• Do a demonstration about commercial yeast.
  • Show students the yeast spores from the package
  • Mix 1/4 c warm water, yeast and 1/4 tsp sugar together and ask what is happening. This mixture should start to bubble. Ask them what is happening. You can say that the yeast is eating the sugar and burping out CO2.
• Where does yeast come from?
  • You can get it from the store in packets. Yeast spores are like seeds. They reproduce and die but their “babies” live on.
  • You can make a starter (at least in our area where the yeast are naturally in the air) by mixing flour and water and leaving it on the counter for a few days.
    • Ask what happened in California in 1849? Tell a brief history of the Gold Rush and the Boudin bakery. They have starter that has supposedly been going that long. Starter will last a long time if you continue to feed it.
    • Yeast was used by the ancient Egyptians to make beer and bread and scientists have studied the bread that was put in the tombs with the mummies.
    • Yeast in spore form can live a long time. Some yeast was extracted from amber that was 45 million years old and then used to make beer in modern times.
• Making Amish Friendship bread starter. Tell students that the process before baking takes 10 days. Flour in dough acts as the walls or scaffolding to trap the CO2 bubbles in the bread.
  • Demonstrate the correct way of how to measure the dry ingredients (flour/sugar) to make the starter.
    • Fill a measuring cup for dry ingredients with flour. In comparison, show them one for liquid measures. Spoon in flour to make a “mountain” and over fill the cup, do an “earthquake” by tapping on the sides of the cup with the straight edge, followed by the “bulldozer” with a straight-edged instrument over the top.
  • The waste CO2 will collect in the Ziplock bag and the class will need to tend to the starter by turning the bag gently (it can be a mess if the bag explodes) and by removing extra gas on a daily basis. On the 5th day, flour, sugar and milk will need to be added.