Question

how do we identify the parts of a controlled experiment?
read the description of the following experiment. then use your knowledge of the scientific method to answer the questions.

a student obtained two identical culture dishes. he labeled them dish 1 and dish 2. he used a cotton swab to transfer the bacteria that was growing in the test tube. then he streaked the swab across both culture dishes. each culture dish received the same kind of bacteria.

to culture dish 1, the student added the antibiotic penicillin. penicillin was not added to culture dish 2. both dishes were placed in an incubator for 72 hours at 37 °c. after 72 hours all the bacteria in dish 1 were dead. the bacteria in dish 2 were alive and many colonies had formed.

1. write a title for the experiment.
2. write a hypothesis for the research.
3. what was the independent variable?
4. what was the dependent variable? how was the dependent variable measured?
5. list the 5 control variables.
6. which dish represented the control in this experiment?
7. what were the results?
8. state a conclusion based on the results.

Explanation:

Answer:

1. The Effect of Penicillin on Bacterial Growth
2. If penicillin is added to a bacterial culture, then the bacteria will die (or be inhibited from growing).
3. Presence/absence of penicillin
4. Bacterial growth (or survival); By observing if bacteria are dead or alive (and colony formation)
5. Identical culture dishes, same swab, same kind of bacteria, same incubation time (72 hours), same incubation temperature (37°C)
6. Dish 2
7. After 72 hours, all bacteria in Dish 1 (with penicillin) were dead; bacteria in Dish 2 (without penicillin) were alive and formed many colonies.
8. Penicillin is effective in killing (or inhibiting the growth of) the tested bacteria.