6A_Is+Yeast+Alive?

**Hypotheses:** Do you expect yeast to produce a gas when sugar is available? Yes Do you expect yeast to produce a gas when sugar or no other food is available? No. //Explanation:// Yeast that is alive will respire and produce CO2 when there is sugar. In the absence of sugar, it cannot respire and thus will not produce any gas.
 * Is Yeast Alive?**

__Results__

**Test Tube** || **Limewater at 0 min** || **Limewater at 20 min** || **Conclusion** || **L** || Clear || White ppt at the surface || Carbon dioxide was produced. || **D** || Clear || Clear || No carbon dioxide was produced. ||

Hypotheses was proven correct since white precipitate appears when limewater is reacted with carbon dioxide.

Amount of gas produced was not measured but could be done with a ______________.

__Results - Activities of yeast cells__

**Test Tube** || **Methylene blue test at 0 min** || **Methylene blue test at 5 min** || **A** || Mixture remains blue || Mixture turns colourless || **B** || Mixture remains blue || Mixture remains blue ||

The live yeast reduced the mixture of the yeast and methylene blue colourless. This is due to a reaction in the yeast cell that reduces the methylene blue, thus decolorizing the mixture. However in the mixture with the boiled yeast, the cells are dead and thus the no reactions can be carried out to reduce and decolorize the yeast cells.

When A and B were shaken, the mixture in A starts to froth while nothing was observed in B. This is as respiration occurred in the yeast cells, which are alive, in A, thus producing carbon dioxide gas which causes the solution to froth when shaken. Whereas in B, the dead yeast cells cannot produce carbon dioxide gas and thus no frothing takes place.

__Examining Yeast cells under microscope (Magnification: 400X)__ Yeast cells are egg (epileptic) shaped.

The yeast from A were mostly colourless but some were faint blue. However, the yeast from B were practically all colored blue.

This is because methylene blue can also be diffused into an yeast cell despite it being alive.

__Discussion__
 * 1) Interpretation of results above.
 * 2) Evidence of yeast cells alive
 * The mixture of live yeast cells and methylene blue turned from blue to colourless in 5 minutes.
 * The mixture of live yeast cells with glucose solution produced CO2, observed when the gas produced reacted with limewater to form a white precipitate.
 * 1) How does yeast help bread dough to rise?
 * The flour in the dough acts as the source of glucose for the yeast. The yeast, upon contact with the flour in the dough will respire and produce CO2, thus creating air spaces in the bread that makes it big and fluffy.
 * 1) 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 a day or two?
 * Yes, because live yeast cells can reproduce asexually.

__Some notes__ Yeast is supended in water, not dissolve. Each yeast granule has thousands of yeast cells in it. Putting it in water merely breaks up the contact that each yeast cell has to one another, thus, the yeast are not dissolved but merely suspended.

**Oxidation- process which involves a loss of electrons.** **Reduction- process which involves a gain of electrons.**