SUPER YEAST! Each Bag That Is Labeled Sugar, and 1 Tsp
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Microbiology in a Plastic Bag! More than just a typical, mild-mannered An easy yeast experiment you can do at home (remember to ask an adult first) Introduction: fungus… Even as far back as ancient Egypt, people were using yeast to make food, such as baking bread. However, nobody knew why adding yeast helped make bread until a famous scientist named Louis Pasteur showed that tiny living organisms called yeast were doing something to make the bread rise. Growing yeast cells love to eat sugars and starches, like the kind found in bread flour. When they eat those starches and sugars, they produce carbon dioxide gas (just like when humans eat food, we breathe out carbon dioxide gas). All of these carbon dioxide gas bubbles get into the bread dough and pop during baking, leaving tiny holes where they were. You can see the tiny holes in the bread you eat. You can buy dried yeast in the grocery store, which is still alive. But it can’t start growing until you give the yeast cells food and water. Let’s see if you can figure out what yeast likes to eat! Materials: 4 zip-lock bags table salt sugar water 4 packets of baking yeast (1/4 ounce each packet) Procedure: Saccharomyces cerevisiae is a 1. Label bags with a marker: sugar, salt, sugar + salt, and water only 2. Add a package of yeast (or 2 teaspoons) to each bag. Add 2 tsp. of sugar to SUPER YEAST! each bag that is labeled sugar, and 1 tsp. of salt to each bag labeled salt. 3. Carefully add ½ cup water to each baggie (it should be warm, but not too hot or it will kill the yeast: around room temperature should work). 4. Seal the bags, squeezing out as much of the extra air as possible and let them sit (the yeast will grow faster in a warm room than a cold one). 5. Check the bags every 5-10 minutes to see what happens. You will know the yeast is growing if the bag puffs up. Keep an eye on your experiment: if the bag gets to full, it could pop open… you can open it up to let the pressure out if needed. Which ingredients help yeast grow best? Did any ingredient prevent growth? What is being made by yeast that makes the bags puff up, and how does this tell you the yeast is growing (hint: check the introduction)? What other variations can you think of and test to learn about how yeast grow? Fun facts about yeast Human uses for S. cerevisiae: The term yeast refers to all single-celled fungi, and includes many different Food and Beverage Industry species. All fungi are more closely related to people than they are to plants! Baking bread requires yeast for making the bread rise Saccharomyces cerevisiae (sack-uh-roe-my-sees sara-vis-ee-ay) is the Cider, beer, wine, sake, whiskey and other beverages require yeast scientific name for the most commonly used yeast in the world. The word to produce alcohol and other flavors “saccharomyces” is from ancient Greek and means “sugar fungus.” The word Yeast extract is high in nutrients, including B-vitamins, and is “cerevisiae” is from ancient Latin and means “of beer.” included in many foods as an additive (check the boxes of foods you regularly eat, and you will likely see that yeast extract is in the Some cultures around the ingredients) world eat dead, ground-up yeast by spreading it on Medicine toast. In Australia, this food About half of the medical insulin in the world used to treat patients product is called Vegemite, with diabetes is made by yeast while in England it is Some vaccines are made by yeast, while some include yeast in the called Marmite. ingredients to help stimulate the immune system (including flu, Yeast cells, like other fungi, have external digestive systems. Yeast cells hepatitis, human papillomavirus, pneumococcus, and typhoid secrete digestive juices, then absorb broken down nutrients from outside the vaccines) cell. By comparison, people bring food into the stomach first, then secrete digestive juices, then absorb broken down nutrients into intestinal cells. Research Yeast has been extensively used to understand how cells work; When two yeast cells want to mate, they form an elongated because most yeast genes are the same as human genes, projection towards each other - this shape of cell was called discoveries in yeast often apply to human biology. a “shmoo” based on a comic strip from the 1940s. The Nobel prize is one of the highest honors that a scientist can receive; at least 8 have been won by scientists for work on yeast (and many more for research that relied on knowledge discovered using yeast) If you filled up the volume of a If you stretched yeast end-to-end, 1907 Eduard Buchner (discovery of cell-free baseball with yeast cells, how many how many would it take to circle fermentation); 1970 Luis Leloir (discovery of sugar yeast would it take? around the earth? nucleotides); 1993 Michael Smith (development of site- directed mutagenesis); 2001 Lee Hartwell and Paul Nurse (discovery of cell cycle regulation); 2006 Roger Kornberg (characterization of eukaryotic gene expression), 2009 Elizabeth Blackburn (characterization of telomeres), 2013 Randy Schekman (characterization About 4 trillion About 4 trillion of vesicular trafficking), 2016 Yoshinori Ohsumi (4,000,000,000,000) (4,000,000,000,000) (characterization of autophagy).