Using Koch's Postulates to Determine the Cause of Milk Curdling into Yogurt

a) Bacterias are prokaryotes that are found everywhere. They can be found everywhere in Earth, and maybe in Mars. There are three major shapes bacteria can take form in. They are the coccus (spherical), bacillus(rod-shaped), and spirillum(spiral). The bacteria increases its numbers by binary fission, which is the process of splitting in half, and can divide in as little as 15 minutes.Even though bacteria is a small micro-organism, it still requires to eat food to gain energy. Bacteria breaks down its food, sugar, by using a process called fermentation. Fermentation in bacteria can either be aerobic(with oxygen), anaerobic(without oxygen), or both(facultative anaerobic. The yogurt bacteria are anaerobic and breaks down the lactose into pyruvic acid, which is then broken down further into lactic acid. Since lactic acid is acidic, the pH level of the milk will go down and be more acidic. Since it is more acidic, the casein, protein in milk, will denature and become more solid. In addition, the low pH will kill the spoilage bacteria, allowing the yogurt to last longer. Many people know bacteria as the micro-organism that causes diseases. However, that is only a small number of bacterias that can cause disease. There are a number of good bacterias, including the Escherichia coli (E.coli). These good bacterias are also known as probiotics and can be found in a number of foods, including yogurt.
In 1676, Anton van Leeuwenhoek saw bacteria under a microscope and called them animalcules. After several attempts to prove the germ theory of disease by many people. In 1875, Robert Koch was able to reveal proof of the germ theory of disease by his set of rules now know as the Koch's Postulates. Koch's Postulate rules, using the scenario of finding the cause of a disease, are:
1. Find microbe in all sick people but not in healthy people
2.Culture that microbe
3.Inoculate healthy people with the that microbe
4.Culture microbe from the new sick people
the results should/shouldn't be that the microbes are the same.

b) The purpose of this experiment is to test Koch's Postulate by practicing microbial techniques to create yogurt.

c) There are four tubes labeled with: milk, milk and yogurt, yogurt with 10 μl ampicillian, and a tube containing E. coli. The tube containing only milk will act as the negative control while the tube with milk and yogurt acts as the positive control. Mix all the tubes in the vortex machine,(Vortex Machine By machine.cc),a machine used to mix small amounts of solution. After mixing all the tubes, place the tubes in an incubator or water bath at 37° C ~ (98° F). When placed in high temperatures, the milk protein, casein, will denature, change shape. When casein is denatured, the milk will become more solid.

d) The control in this experiment is the milk tube. The variables in this experiment are the tubes with milk and yogurt, yogurt with ampicillian, and the tube with E. coli. I predict that the tube containing yogurt and milk will be the tube that forms the best yogurt because it already contains yogurt in the tube. So when the casein denatures, the mix will to from  semi-liquid to semi-solid due to the yogurt.