Week 9 Biology Lab & Inquiry: Counting Mitosis in the Onion Root Tip

Part 1 — The Big Picture

This week you learned that the cell cycle is a loop, G1 → S → G2 → M, with most of a cell's life spent in interphase, and that mitosis runs prophase, metaphase, anaphase, telophase, in that order. In this lab you see that loop in real cells. The tip of an onion root is a growing tissue, so at any moment some of its cells are caught in the act of dividing. With a free virtual microscope you sort photographed root-tip cells into interphase and the four phases of mitosis, using one clue for each. Then you count each stage, compute the mitotic index, the share of cells in mitosis, and turn your shares into hours on a 24-hour cycle. Last, you check a chatbot's account of your lab and catch where it scrambles the order, confuses mitosis with meiosis, mislabels a structure, oversimplifies cancer, or invents a number.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: In a growing onion root tip, what share of cells is dividing at any moment, and what does that share say about how a cell spends its time in the cell cycle?

Before you begin — hypothesis: Before you classify any cell, write one hypothesis in the if… then… because… form: if the onion root tip is a growing tissue, then most of the cells you see will be in one particular stage, because of a reason about how long a cell spends in each part of the cell cycle that you can state. Then predict which phase of mitosis will hold the most cells.

Workshop data: Your own onion root-tip cell count, or the illustrative fallback count

Source: Cell counts you record yourself by classifying the photographed onion root-tip cells in the virtual microscope activity named in Part 3; if you cannot run the activity, use the illustrative fallback count printed in the fallback, which was constructed for this lab and is not real data.

• Rows: one row per stage of the cell cycle you count (interphase, prophase, metaphase, anaphase, and telophase), so the count table has 5 stage rows plus a total row; the first scaffold table has 5 rows that name the parts of the count rather than data, and the reasoning table has 3 rows
• Columns: stage, number of cells you counted in that stage, and that stage's share of all cells counted
• Unit: a count of cells, one tally mark per classified cell

Part 3 — Materials & Procedure

Tools and materials

• Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet)
• A web browser and an internet connection
• A document or notebook for your written answers

Ways of working

• virtual-simulation-inquiry
• at-home-protocol-and-data-table
• figure-and-diagram-interpretation

Procedure

1. In a web browser, open The Biology Project's Online Onion Root Tips activity from this week's Readings & Resources page. Read its page that describes the five stages, then move on to the first cell. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: The activity shows one photographed onion root-tip cell at a time with five buttons: interphase, prophase, metaphase, anaphase, and telophase.
2. Before you classify any cell, fill in the first table in Part 4: your if… then… because… hypothesis, a prediction of which stage will hold the most cells, and the parts of the count. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: The first table has a hypothesis, a prediction, and the counted cells and the stages named.
3. Classify each cell by clicking the stage you see, using one clue each: condensed rods with no envelope for prophase, one row across the middle for metaphase, two groups moving apart for anaphase, two nuclei re-forming for telophase, and a whole nucleus with no visible chromosomes for interphase. If the activity says to try again, read its hint and choose again. Make a tally mark for the stage the activity accepts. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Each cell earns one tally mark in exactly one stage.
4. When the activity shows every cell sorted by stage, count each stage on screen and check the count against your tally. Write the five counts in the count table, then add them to get your total. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: The five counts add up to the number of cells you classified.
5. Open a blank sheet. Type the five stage names into cells A2 to A6 and your five counts into B2 to B6. In B7 type =SUM(B2:B6), in B8 type =SUM(B3:B6), in B9 type =B8/B7*100, and in B10 type =B9/100*24. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: B7 equals your total, B8 equals your cells in mitosis, B9 equals your mitotic index, and B10 equals your hours of mitosis on a 24-hour cycle, each matching your hand arithmetic.
6. Complete the reasoning table, answer the analysis questions in your document, then paste your completed tables into an approved chatbot with the prompt in Part 6 and check its answer against the scripted checks. Tool: Free virtual labs and simulations (PhET, HHMI BioInteractive, Learn.Genetics), a virtual microscope, and a spreadsheet (Google Sheets or any free spreadsheet). Check: Completed tables, written answers, and a list of the chatbot's errors with corrections.

Fallback route

When to use it: Use this route if the virtual microscope activity will not load, or if you cannot get online long enough to classify the cells.

Use the illustrative fallback count below, constructed for this lab and not real data, as your count table, then complete every scaffold table, analysis question, and the critique step from it and submit the same items for equal credit. Fill the empty column yourself.

This route earns the same credit as the primary route.

An illustrative fallback count of 50 onion root-tip cells, constructed for this lab, that stands in for your own count.

Fallback model data

Stage	Cells counted	Share of all cells counted
Interphase	41
Prophase	4
Metaphase	2
Anaphase	1
Telophase	2
Total	50

Part 4 — The Scaffold

Name every part of the count before you classify a cell, so your prediction is on record first.

Student scaffold table 1

Part of the count	Your answer
Hypothesis (if… then… because…)
Prediction: the stage that will hold the most cells
Prediction: the phase of mitosis that will hold the most cells
What you are counting
Which stages count as dividing, and which do not

Record how many cells landed in each stage, then work out each stage's share of everything you counted.

Student scaffold table 2

Stage	Cells counted	Share of all cells counted
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total

Explain the three results that matter most, from what you know about the cell cycle.

Student scaffold table 3

Question	Your reasoning
Why do most cells sit in interphase?
Which cells go on the top of the mitotic index, and which go on the bottom?
Why can a share of cells stand in for a share of time?

Part 5 — Analysis Questions

1. Show the sum of your five counts, the sum of the four mitosis phases, the division and multiplication for your mitotic index, and your hours of mitosis and of interphase on a 24-hour cycle; check that the two hour figures add to 24.
2. Which phase of mitosis held the most cells in your count, and which held the fewest? Using the idea that a longer stage catches more cells, say what your count suggests about which phase lasts longest.
3. Does your evidence support or fail to support your hypothesis? Write one conclusion sentence that uses supports or fails to support rather than proves, and explain where in the cell cycle the DNA is copied and why that stage is not counted as dividing.
4. A healthy root tip divides fast. Explain why fast division alone does not make a tissue cancerous, naming checkpoints and a tumor-suppressor gene such as p53, and explain why many cancer drugs that hit dividing cells also hit hair follicles.
5. Choose one and answer it in 3–4 sentences. (a) Your count comes from a small set of photographed cells from one root: name one way a different slice or a larger count could change your index, and say what you would do to make the estimate more trustworthy. (b) Some cells are hard to classify, such as a cell between two phases: name one such case, say how it could shift your shares, and say what rule you would follow to classify it the same way every time.

Part 6 — AI-Critique Moment

Choose one equal-credit critique route. Route A: ask an approved AI tool to critique your completed work, then check its response against your own evidence. Route B is the no-AI equivalent printed below.

Approved tools: Claude, Gemini, ChatGPT, Grok, Microsoft Copilot.

Prompt to paste:

I've pasted my completed Week 9 Biology Lab & Inquiry tables above. I classified photographed onion root-tip cells into interphase, prophase, metaphase, anaphase, and telophase with a virtual microscope, then counted each stage. Please do seven things. First, list the stages of the cell cycle in order and say when the DNA is copied. Second, describe what happens in each phase of mitosis, in order. Third, check my mitotic index and my hours of mitosis on a 24-hour cycle, showing each division and multiplication. Fourth, tell me how many cells and how many chromosomes per cell mitosis makes from one human body cell with 46 chromosomes. Fifth, explain in two sentences what cancer is in terms of the cell cycle. Sixth, tell me the exact mitotic index a real onion root tip should have, with its source. Seventh, as a stretch question for later in the course, say what phenotype ratio a cross of two Tt parents gives.

Test the response for these likely failures:

• Chatbots sometimes swap metaphase and anaphase, or say the DNA is copied during mitosis, in prophase, instead of in the S phase of interphase.
• Chatbots sometimes say mitosis makes four cells or halves the chromosome number to 23, which describes meiosis.
• Chatbots often call an X-shaped duplicated chromosome two chromosomes, mix up chromosome and chromatid, or give an animal cell a cell plate.
• Chatbots often describe cancer as cells that divide fast, or compute the mitotic index by dividing the dividing cells by the interphase cells.
• Asked for a real onion mitotic index, chatbots often state a precise percentage and cite a study or source that was never given.
• Asked the stretch question, chatbots sometimes give the phenotype ratio of a Tt by Tt cross as 1:2:1, which is the genotype ratio.

Write 3–5 sentences naming one thing the chatbot got right and at least two places it went wrong or overreached, quoting its words and correcting each with evidence from your own tables or this week's chapter; mark the stretch answer as one to check in a later week.

Equivalent route (no AI required)

No AI account is required for this lab. Instead of the chatbot, critique this flawed analysis, printed here in full: "My onion cells show the cell cycle running prophase, anaphase, metaphase, telophase, and the DNA gets copied during prophase, when the chromosomes appear. Each X I saw was two chromosomes stuck together, and every onion cell finished by pinching in at a cleavage furrow. I worked out the mitotic index by dividing my dividing cells by my interphase cells. A root tip divides this fast, so it is a lot like cancer, which is only cells dividing quickly. A real onion root has a mitotic index of exactly 31%, as a study shows. Mitosis will end with four cells that each have half the chromosomes. As a preview of a later week, a cross of two Tt parents gives a 1:2:1 phenotype ratio." Mark it up: quote each flawed sentence, name what is wrong (a stage out of order, a mislabeled structure, an over-simplified mechanism, an invented figure, mitosis confused with meiosis, or a preview fact stated wrong), cite the evidence from your tables or this week's chapter, and write a corrected sentence beneath it; for the preview sentence, say which later week will check it. This route assesses the same objective (Objective 5 — describe the eukaryotic cell cycle and the ordered phases of mitosis, compute a mitotic index, contrast mitosis with meiosis, and explain how crossing over, independent assortment, and fertilization generate genetic variation, including the 2ⁿ count) as the chatbot critique, takes comparable effort (about 30 minutes and 200–300 words), is scored by the same scoring criteria for the same credit, and its own submission artifact is the marked-up flawed analysis, posted in place of the chatbot share link and report.

Part 7 — What to Submit

• All three completed scaffold tables, filled from your own count or the illustrative fallback count
• Written answers to all five analysis questions
• The chatbot critique report with its share link, or the equivalent route's marked-up flawed analysis

Deliverable:

A short Biology Lab & Inquiry report on the onion root tip: three completed tables (the named parts of the count, the counts for each stage with their shares, and the reasoning about interphase, the index, and time), written answers to five analysis questions, and a critique of a chatbot's account of your lab, or, on the equivalent route, a marked-up correction of the printed flawed analysis. 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. Choose a written, recorded, or visual form for your answers; every form is graded by the same scoring criteria.

Rubric

The rubric below shows how each submitted part is evaluated; bands are full, partial, or none.

Workshop evaluation criteria

Criterion	Full	Partial	None
Testable hypothesis and prediction	A falsifiable if… then… because… hypothesis and a prediction of the most common stage and phase appear before any cell is classified, and the dividing and non-dividing stages are named correctly.	A hypothesis appears but is not falsifiable or lacks a prediction, or interphase is counted as a dividing stage.	No hypothesis, or the parts of the count are not named.
Completed count table with the mitotic index and hours	All five stages have counts from the student's own classified cells or the fallback count, the shares are correct for those counts, the mitotic index divides the cells in mitosis by every cell counted with each step shown, and the hours of mitosis and interphase are correct and add to 24.	The table is filled, but one or two shares, the index, or the hours are wrong, or the divisions and multiplications are not shown.	No counts are recorded, or the counts are invented rather than classified or taken from the fallback.
Cell-cycle analysis and the cancer connection	Questions 1 to 4 are answered accurately: the conclusion uses supports or fails to support, the DNA copying is placed in the S phase of interphase, the most and least common phases are read from the count, and fast healthy division is kept apart from cancer through checkpoints and a tumor-suppressor gene, with the hair-follicle link explained.	The questions are attempted, but one or two answers place the DNA copying in mitosis, put the phases out of order, call fast division cancer, or claim the result proves the hypothesis.	The analysis questions are missing or do not address the results.
Critique of the chatbot or of the printed flawed analysis	On either route, at least two errors are quoted and corrected with evidence from the student's own tables or the chapter, the stretch answer is marked to check later, and one correct point is acknowledged; both routes earn this band equally.	On either route, errors are named but corrected without evidence, or only one error is caught.	No critique appears, or pasted output is submitted without any checking.
Reflection on the limits of the count	The chosen reflection option is answered in 3–4 sentences that tie a specific limit of the count, or a specific hard-to-classify case, to a concrete change in the count or in what can be claimed.	The reflection is answered but stays general or names no specific change.	No reflection is submitted.

Quality Gate

• Every count in the count table comes from your own classified cells or the printed fallback count, never from memory or a chatbot.
• The mitotic index shows its sum, its division by every cell counted, and its multiplication by 100, and the hours show their multiplication by 24.
• The hypothesis was written before the first cell was classified and has the if… then… because… form.
• The DNA copying is placed in the S phase of interphase, never during mitosis, and the phases are given in order.
• No measurement, rate, percentage, study, or source is invented anywhere in the submission.
• The critique quotes the chatbot or the flawed analysis and corrects at least two errors with evidence from your tables or the chapter.