Introduction:
a) Background
In this lab we are using bactaeria to change milk into yogurt. Bacteria is actually the most successful life form on the entire planet! There is even evidence that bacteria might exist on other planets, like mars. Bacteria are prokaryotes, which are creatures with single-cells. They are so tiny that one inch would be filled eith up to 50,000 bacteria. Normally people think that bacteria are harmful and cause disease, but only a small portion of bacteria are dangerous. Bacteria is also the cause of milk spoilage. However, not all bacteria has negative effects. E.Coli is a type of bacteria that is actually beneficial and necessary for bodies to function correctly. There are a few different types of bacteria, such as coccus, bacillus, and spirillum.
b) Purpose
Bacteria has many purposes. It is used to make yogurt from milk by breaking down lactose into pyruvic acid, and creating lactic acid using enzymes. Bacteria also demonstrate's Koch's postulates and show that a microorganism can cause a certain disease.
c) Procedure
In this lab, we are going to create yogurt from milk. In order to do this we must pasteurize milk by heating it up and quickly cooling it down. Pasteurization kills bad spoilage bacteria. Next, add some yogurt (fage yogurt for this lab. Then mix the yogurt and the milk together and store it for 24 hours. The next day you will have yogurt! The milk sugar (lactose) created lactic acid. The change in pH created a milk protein known as casein and that was denatured. It changed from liquid to solid form. Lowering the pH kills all spoilage bacteria so it does not go rancid easily.
d) Controls/Variables/Prediction
The controls in this lab are Milk, and Milk and Yogurt. The Variables are Yogurt and ampicillin, and E. Coli. My prediction is that E. Coli helps to prevent the yogurt from spoiling. Also, as some sources of error for this lab, one could add the incorrect amount of ampicillin. Ampicillin is an antibiotic, so if there is not enough of it, the bacteria could cause the milk to spoil.
Summary/Results/Possible Sources of Error:
In this lab, I learned how to apply Koch's Postulates. We had 4 tubes containing milk, milk & yogurt, yogurt & ampicillin, and E Coli. The first two tubes were the controls and the second two were the variables in the experiment. We inoculated milk with yogurt and the yogurt+amp. We added E Coli into the tube containing E Coli. By adding bacteria from yogurt to milk showed Koch's 3rd postulate, the cultured microorganism should cause disease when introduced into a healthy organism. All bacteria doesn't turn milk into yogurt, as proven when adding E Coli. Adding ampicillin, an antibiotic, into one of the tubes acted as a control so that we knew what is the yogurt bacteria. As possible sources of error, I could have added too much or too little ampicillin into the test tube. Adding too little could have made the yogurt go rancid, and adding too much could have killed too much bacteria and not created milk. We could have also not pasteurized the milk correctly, so some spoilage bacteria could have been left over. So as a summary, Tube 1 with milk alone resulted with white, liquid milk with a pH of 6. Nothing reacted with the milk except the bacteria that was pre-existent. Tube 2 with yogurt and milk created thick, white yogurt with a tart/sour smell and a pH of 4. The bacteria in yogurt reacted with the milk to create yogurt. The pH changed and changed the state of the solution to a solid. Tube 3 with yogurt and ampicillin resulted in a liquid, white milk with a pH of 7. The ampicillin killed the yogurt bacteria so it was changed back into liquid form. Finally, tube 4 with E Coli created a murky white liquid that smelled like sour milk and had a pH of 8. Although a type of bacteria, E Coli did not create yogurt. The control yogurt cup had a pH of 4.
