Is+Yeast+Alive?

Yeasts are eukaryotic micro-organisms classified under the kingdom //Fungi//. Some common uses of yeasts include: ** > Alcoholic beverages: //Used for fermentation.// > Baking: //Used in baking as a leavening agent, converting the fermentable sugar present in dough into carbon dioxide, causing the dough to expand or rise as gas forms in pockets or bubbles.// > Bioremediation > Industrial ethanol products: // The ability of yeast to convert sugar into ethanol that has been harnessed by the biotechnology industry to produce ethanol fuel. // > Non-alcoholic beverages (e.g. root beer): // Produced the same way as beer, except fermentation is stopped sooner, producing carbon dioxide, but only trace amounts of alcohol. A significant amount of sugar is left in the drink. // > Nutritional supplements: // A nutritional supplement popular with vegans and the health conscious. Referred to as 'nutritional yeast'. It is an excellent source of protein & vitamins, especially the B-complex vitamin. // > Probiotics: // Some probiotic supplements use the yeast // Saccharomyces boulardii // to maintain and restore the natural flora in the large and small gastrointestinal tract. // > Aquarium hobby: //Used to generate carbon dioxide to fertilize plants in planted aquariums.//
 * Humans use yeast everyday. What is yeast, and what are some common uses of yeast?

//** You can buy yeast to make bread in the grocery store. This yeast consists of little brown grains. Do you think that these little brown grains of yeast are alive? Why or why not? They are alive. If they're not alive, they are unable to perform the functions yeasts are supposed to function, such as leavening the dough.

**To find out whether yeast is alive, we first need to think about what makes something alive. What are some characteristics of living organisms? Reproduction Irritability Nutrition Growth Excrete Respire

Carbon dioxide is produced. It can be identified using limewater as limewater turn chalky in the presence of carbon dioxide.
 * We will test whether yeast can metabolize sugar and produce a gas in the process. What gas do you think is produced? How will you identify it?

**Hypotheses: Do you expect yeast to produce a gas when sugar is available? //Yes//. Do you expect yeast to produce a gas when no sugar or other food is available?// No. Explain the reasons for your predictions: Carbon dioxide is a product of respiration and is formed when the yeast respires. When there is no food, no sugar, respiration cannot take place. Hence, no carbon dioxide is formed.

How would you measure the amount of gas given? //By using an equipment...Counting the number of bubbles formed...Assessing the level of chalkiness of the limewater.//
 * Procedure to Test Your Predictions

How do you determine the identity of the gas? //By performing experiments, as different setups can determine whether the gas is X or not. For this, limewater is used as it can determine if the gas is carbon dioxide—limewater turns chalky in the presence of carbon dioxide.//

**// Discussion 1. How do you interpret your results? //Yeast requires sugar to respire.

2. What are the evidences that prove that the yeast cells are alive? //The boiled yeast, which are dead, did not produce any carbon dioxide through respiration while the unboiled yeast did. This shows that the boiled yeast are dead while the unboiled ones are not.// 3. When you make bread, if you just mix flour, sugar and water, the dough does not raise, and the bread will be flat and hard. If you include yeast in the bread dough, then the dough rises and the bread is bigger and fluffier. Can you explain how the yeast helps the bread dough to rise? //By adding yeast to the mixture, the yeast would respire in the presence of food and sugar. This will produce carbon dioxide in bubbles/pockets, making the bread softer and fluffier.// 4. If we were to place a few grains of the yeast in a yeast culture, do you think you will be able to see any growth after one or two days? //Yes.

Methylene blue is an indicator to test whether the chemical is reduced or oxidized.

Yeast cells cannot help the diffusion of methylene blue through their cell membranes. However, the life yeast cells will readily oxidized the colored methylene blue so they are no longer blue. Only the dead ones are colored. //