Bacteria Lab Hypothesis Formation
Step 1: Using your textbook and the internet, research the following questions. This is background information
that will help you form your hypothesis. Answers should be in your own words. Keep track of your sources – you
need a bibliography.
1. What is an antibiotic?
2. Some bacteria are gram positive and some are gram negative. What does this mean?
3. Is E. coli gram positive or gram negative?
4. Is M. luteus gram positive or gram negative?
5. What are some commonly used antibiotics?
6. Do all antibiotics work equally well with all bacteria?
7. What is a “broad spectrum” antibiotic? How effective is it at controlling the growth of gram positive and
gram negative bacteria?
8. Is penicillin more effective at controlling the growth of gram positive bacteria, gram negative bacteria, or
does it work equally well on both?
9. Is tetracycline more effective at controlling the growth of gram positive bacteria, gram negative bacteria, or
does it work equally well on both?
10. Is streptomycin more effective at controlling the growth of gram positive bacteria, gram negative bacteria, or
does it work equally well on both?
Step 2: These instructions are designed to help you form your hypothesis, complete with a summary of your
background research. Use the information learned from answering the questions above as you complete the
following steps:
1. Write a short paragraph about penicillin, tetracycline and streptomycin. Describe their comparative
effectiveness on gram positive and gram negative bacteria.
2. Write a short paragraph about E. coli. Be sure to include how it reacts to the gram stain and what this
reaction tells you about the bacterium.
3. Based on what you wrote in the two questions above, write your prediction of what will happen to a culture
of E. coli when you add each of the three antibiotics. Will the culture grow? Be specific.
4. Now use your prediction to make a statement which represents your hypothesis 1 for the lab. The
statement should contain the words: If. . . then. . . because.
If (this is done) then (this will happen) because (state reason).
* For example, imagine you have a flashlight that doesn’t work and you want to know why. You might come
up with the hypothesis, “If I change the batteries, then my flashlight will work because the old batteries are
dead.”
5. Write a short paragraph about M. luteus. Be sure to include how it reacts to the gram stain and what this
reaction tells you about the bacterium.
6. Based on what you wrote in questions 1 and 5, write your prediction of what will happen to a culture of M.
luteus when you add each of the three antibiotics. Will the culture grow?
7. Now use your prediction to make a statement which represent hypothesis 2 for the lab. The statement
should contain the words: If. . . . . . . . Then. . . . Because.
If (this is done) then (this will happen) because (state reason).
Type and print your answers to both parts and bring them to class on Day 7. Include a bibliography.