Week 1 — Reading a Controlled Experiment: The Penny Lab Report — Traditional alternative (no AI)

Instructors: publish this instead of the adaptive version if you prefer, and unpublish or delete the adaptive one.

Assignment 1 of the term — read a controlled experiment from its numbers to its conclusion and explain it to someone new to biology.

This week you learned that biologists recognize life by a whole checklist and test their ideas with controlled experiments instead of trusting them. In this assignment you work four short problems on one small experiment, interpret each one, and explain the result to someone who has never studied biology. This week's lecture tutorial, quiz, discussion, and Biology Lab & Inquiry practise the same ideas from other angles.

The task

A penny was filled one drop at a time with water until the dome of water spilled over the edge. The drops on a penny experiment is an illustrative dataset constructed for this course (not real data). Three trials used plain water and held 28, 30, and 32 drops. Three trials used soapy water and held 12, 14, and 16 drops. The plain-water average is 30 drops and the soapy-water average is 14 drops.

Work these four problems, showing your arithmetic:

1. Add the three plain-water trials from the drops on a penny experiment (28, 30, and 32 drops). What is the total, in drops?
2. The three soapy-water trials total 42 drops. Divide by the number of trials (3). What is the soapy-water average, in drops?
3. Plain water averaged 30 drops and soapy water averaged 14 drops. How many fewer drops, on average, did the penny hold with soap?
4. The largest plain-water trial held 32 drops and the smallest held 28 drops. What is the range of the plain-water trials, in drops?

Beside each answer, add one brief interpretation:

• Problem 1: name the independent variable and the dependent variable, and explain why the experiment runs three trials per condition instead of one.
• Problem 2: name the control group and explain why the soapy-water result means something only when compared with it.
• Problem 3: express the difference as a share of the control's average, showing the division, and name one confound, a second difference between the groups, that the design must keep out.
• Problem 4: compare the spread of the trials with the gap between the averages, then write a one-sentence conclusion that uses "supports" or "fails to support" rather than "proves," and name one result that would have counted against the hypothesis.

Explain it to a non-expert

Your roommate sees the penny on the counter and asks, "So does soap make water weaker, or was it luck?" Write a 3–5 sentence message that explains what the test changed and what it measured, reports the result in everyday words, and names one limit, including that these numbers are illustrative and that three trials can support a claim but never prove it. Explain any technical term in everyday words. More than one good answer is possible.

For a different, ungraded example, imagine a café that tests whether a new lid keeps coffee warmer on a walk. Model answer: "We tried two kinds of cups on the same walk, changing only the lid, and checked how warm the coffee felt at the end. The cups with the new lid stayed warmer each time we tried. The weather and the walk were the same for both, so the lid is the likely reason. We only tried it a few times on one day, so the result supports the idea but does not prove it; a cold, windy day might change things."

Use that pattern for the penny experiment, with your own wording and evidence.

Show your arithmetic. A reader should be able to reproduce every number you report from the six trial counts without guessing which values or steps you used.

Deliverables

Submit a single lab report containing:

• the four answers, each with the arithmetic shown and the brief interpretation the task names for that problem;
• your message to your roommate, explaining what the test changed and measured, the result in everyday words, and one limit; and
• a one-line restatement of the six trial counts you used, so your results are reproducible.

Keep it to roughly one page. Clear and correct beats long.

Choose how you show it. Present your report as written text, or as a recorded audio or video explanation of about three minutes with a transcript, or as a labelled sketch of the six trials with a short note. Every form is graded by the same scoring criteria. Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text.

How you'll be graded

The full analytic rubric is attached to this assignment in Canvas.

Academic integrity and AI use

This version is designed to be completed without AI: do the computations, the interpretations, and the writing yourself, without a chatbot or other AI tool. You may use a calculator or a spreadsheet for the arithmetic. Submitting AI-generated work as your own, or copying another student's work, is an integrity violation under the course policy.

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