3.2: Exercises

Exercise A: How Penicillin Was Discovered

In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria growing in culture dishes. He noticed that a mold called Penicillium was also growing in some of the dishes. A clear area formed around the mold, indicating that the bacteria in this area had died. In the culture dishes without the mold, no clear areas were present. Fleming hypothesized that the mold must have produced a chemical that killed the bacteria. He decided to isolate the substance and test it to see if it would kill bacteria. Fleming transferred the mold to a nutrient broth solution. This solution contained all the materials the mold needed to grow. After the mold grew, he removed it from the nutrient broth. Fleming then transferred some of this broth onto a culture of bacteria. He observed that the bacteria died. This finding was later used to develop the first antibiotic, penicillin, which was used to treat a variety of bacterial diseases.

Exercise B: Identify the Controls and Variables

1. Muhammad thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they're supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given the special juice. After an hour, Muhammad counts how many stacks of papers each group has made. Group A made 1,587 stacks; Group B made 2,113 stacks.

2. Sophia notices that her shower is covered in a strange green slime. She reads on social media that coconut juice will get rid of the green slime. Sophia decides to test this claim by spraying half of the shower with coconut juice. She sprays the other half of the shower with water. After three days of "treatment" there is no change in the appearance of the green slime on either side of the shower.

3. Anh was told that a certain anti-itch cream was the newest and best one on the market: it claims to reduce itching 50% longer than the leading brand. Interested in this product, she buys the anti-itch cream and compares it to her usual product. She finds two subjects that have itchy mosquito bites. Test subject A applies the original anti-itch cream, and test subject B applied the new anti-itch cream. Subject A reported their itching returned after two hours. Subject B reported their itching returned after one hour and 45 minutes.

4. Lisa is working on a science project. Her task is to answer the question: "Does Rogooti (which is a commercial hair product) affect the speed of hair growth". Her family is willing to volunteer for the experiment.

The Introduction, Exercise A, and Exercise B are adapted from the following:

Burran, Susan and DesRochers, David, "Principles of Biology I Lab Manual" (2015). Biological Sciences Open Textbooks. https://oer.galileo.usg.edu/biology-textbooks/3(opens in new window)

Part of the Biology Commons. Follow this and additional works at: https://oer.galileo.usg.edu/biology-textbooks

This Open Textbook is brought to you for free and open access by the Biological Sciences at GALILEO Open Learning Materials. It has been accepted for inclusion in Biological Sciences Open Textbooks by an authorized administrator of GALILEO Open Learning Materials. For more information, please contact [e-mail].

Exercise C: Reporting Scientific Work

C.1 What is a primary reference?

C.2 Name two peer-reviewed scientific journals in the field of Biology.

C.2 Use the internet to find a peer-reviewed journal article related to cell and molecular biology. Then, in your own words, write a summary of the research (1-2 paragraphs). Include the full reference citation.

Exercise D: Designing an Experiment

We will split the class data into two groups, those that we consider to be athletic and those that are not. We want to know if athletic individuals have lower resting pulse rates than nonathletic individuals. For our lab study, we will consider athletic individuals to be anyone that exercises three hours a week, or more. Lastly you will make a graph of the class data and evaluate your hypothesis (supported or falsified).

D.1 Create a testable hypothesis.

D.2 Create a prediction (if your hypothesis is true, then what results do you expect?).

Data collection: Each student will measure their pulse rate ten times and calculate the average. Be sure to be seated and calm for at least ten minutes prior to taking your pulse. Record your data in the table below and share your average with the class.

D.3 What are the controlled variables in our experiment?

D.4 What is the control group?

D.5 What is the level of treatment?

HR beats per 15 s and per minute

Measurement	1	2	3	4	5	6	7	8	9	10
Beats per 15 seconds
Beats per minute

Table 1. Individual Resting Pulse Rates

D.6 What is your average resting pulse rate in beats per minute (bpm)? _________ Place your average resting pulse rate onto the white board, make sure you correctly assign yourself as an athlete or non-athlete.

D.7 How many students are in the class? _______ How many students are athletic? ______ How many students are not athletic? ________

D.8 Copy the class information into the table below and calculate the class averages.

BPMs and averages of athletes vs. nonathletes

	Athletic	Nonathletic
List of individual pulse rate averages (bpm)
Class average (bpm)

Table 2. Summary of Class Data: Resting Pulse Rates of Athletic and Nonathletic Individuals

D. 9 What was the independent variable for our experiment? On which axis would you graph this?

D.10 What was the dependent variable for our experiment? On which axis would you graph this?

D.11 Design a graph that shows the relationship between the dependent and independent variables in the experiment. Should you use a line graph or a bar graph? Remember to give the graph a proper title, label your x-axis and y-axis, and include their units. Use a separate sheet of paper and staple it to this lab.

D.12 Drawing conclusions: Does the data support your hypothesis?

Exercise E: Design Your Own Experiment 

During exercise muscle metabolism increases, resulting in an increase in the production of CO₂. Interestingly, however, our blood levels of CO₂ do not change significantly during exercise because the increased rate in CO₂ production is matched by a greater rate of CO₂ elimination by the body (respiratory rate and depth increase during exercise). The equation below describes how CO₂ is transported through the blood and is important in the study of respiration and acid-base balance. 

CO₂ + H₂O --> H₂CO₃ --> H⁺ + HCO₃^-

First, read the procedure. Then, complete the Experimental Design section below. After completing the experiment, record and explain your results.

A.      Procedure:   

1. Fill a 250 mL beaker with 200 mL of distilled water and add 5.0 mL of 0.10N NaOH and one or two drops of phenolphthalein indicator (turns pink in alkaline solutions; is clear in neutral/acidic solutions). Mix well and pour half of this solution into a 150 mL beaker (save this for later). 
2. Select one student in your group to volunteer for this experiment. This student’s results will be examined at rest and after 2-5 minutes of vigorous exercise.
3. Student: sitting quietly, exhale through two straws into the solution in the 250 mL beaker. Cover the beaker with a paper towel to avoid splashes. Be careful NOT to inhale or drink the solution. Group members: record the time required to turn the solution from pink to clear.
4. Time at rest (pink to clear): _____________________________
5. Discard this first solution. Pour your saved solution from the 150 mL beaker into the 250 mL beaker, replace the two straws and cover with a paper towel.
6. Student: exercise vigorously with your group members for 2-5 minutes (find a safe and clear area outside of the lab room to do jumping jacks, etc. Heart rate and breathing rate should be increased.)
7. Student: repeat step 3 immediately after exercise (before your heart rate and breathing rate return to normal). Be careful NOT to inhale or drink the solution. Group members: record the time required to turn the solution from pink to clear.
8. Time after exercise (pink to clear): _____________________________
9. Discard the solution and straws. Rinse and replace the glassware. 

B.      Experimental Design:

Question: _________________________________________________________________________

Testable hypothesis: ________________________________________________________________

Dependent variable: ________________________________________________________________

Independent variable: _______________________________________________________________

Controlled variables: _________________________________________________________________

Control: ___________________________________________________________________________

Level of treatment: __________________________________________________________________

Replication: ________________________________________________________________________

Prediction (if/then): _________________________________________________________________

__________________________________________________________________________________

C.      Do your results support or refute your hypothesis? Explain your findings below: