Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Module: Week 9 of 16 · Fall 2026 · in-person, two 75-minute lectures + one weekly lab
Objective covered: Objective 5 — Explain how cells divide: the stages of the cell cycle and mitosis, their purpose, how division is controlled, and how to measure it with the mitotic index.

This file holds two pieces: (A) the Module 9 Overview page ("Start Here") and (B) the Welcome Announcement that drips out when the module opens. Dates below assume a Tuesday/Thursday lecture pattern with Week 9 meeting Tue Oct 27 and Thu Oct 29, a lab that same week, and end-of-week work due Sunday Nov 1, 11:59 p.m. Adjust the day-of-week and times to match your section.

(A) Module 9 Overview — Start Here

Welcome to Week 9: The Cell Cycle & Mitosis

This is your home base for the week. Read it first, then work the checklist below from top to bottom. Everything you need is linked inside the module.

We're back from the midterm and starting a brand-new arc: how one cell becomes two. You started as a single fertilized cell, and you now have tens of trillions — every one made by the same repeating process. This week answers a deceptively simple question: how does a cell copy itself, exactly, billions of times without losing its place? We'll walk the cell cycle (the long growth phase plus the short division phase), put the four stages of mitosis in their non-negotiable order, and learn what happens when the cell's safety checks fail — which is, at an overview level, what cancer is. And because biologists don't just describe division, they measure it, you'll learn to compute a mitotic index from a real cell count.

The week's big question

"How does one cell become two identical cells — in a precise, controlled, repeatable order — and how do we measure how fast it's happening?"

By Friday you'll be able to lay out the cell cycle, put the mitosis phases in order, explain the difference between a chromosome and a chromatid, say why mitosis makes identical cells (and why that's the opposite of what meiosis does next week), and calculate a mitotic index from a count of cells.

By the end of this week, you can…

Use this as a checklist. If you can do all four out loud, you're ready for the quiz.

• [ ] Lay out the cell cycle — interphase (G1 → S → G2, with DNA copied in S) followed by the M phase (mitosis + cytokinesis) — and explain that most of a cell's life is spent in interphase.
• [ ] Order the four phases of mitosis — Prophase → Metaphase → Anaphase → Telophase ("PMAT") — plus cytokinesis, and say in one line what happens in each.
• [ ] State mitosis's purpose — growth, repair, and asexual reproduction → two genetically identical diploid cells — and distinguish a chromosome from a chromatid.
• [ ] Compute a mitotic index — (cells in mitosis ÷ total cells) × 100 — and explain why checkpoint failure leading to uncontrolled division is, in overview, what cancer is.

What's due this week, and when

Work these in order — each one gets you ready for the next.

Heads-up on the AI tools: you'll use a chatbot to draft and explain, and then you judge its work against what we cover in class. Chatbots routinely confuse mitosis with meiosis (they'll say it makes four cells, or gametes, or halves the chromosome number) and mis-order the PMAT phases. Catching the model is the point — in the tutorial, the assignment, and the lab.

Late policy reminder: 10% off per day late. If life happens, reach out before the deadline — I'd much rather hear from you early.

How to succeed this week

• Lead with the idea, not the jargon. Mitosis is just make one exact copy and split. Every term — chromatid, centromere, metaphase plate — is a plain-English idea first; the vocabulary comes after the picture clicks.
• Memorize two tiny hooks. "PMAT" for the phase order (Prophase, Metaphase, Anaphase, Telophase). And "mitosis makes two; meiosis makes four" — so you never mix this week up with next week.
• Get the chromosome-vs-chromatid picture straight. A duplicated chromosome is an X — two sister chromatids joined at the centromere. They split apart in anaphase. Draw it once and the whole week gets easier.
• Do the mitotic-index arithmetic by hand. (cells in mitosis ÷ total) × 100. If 20 of 100 cells are dividing, that's 20%. Doing it once makes the lab and the quiz easy.
• Treat the chatbot as a smart intern, not an oracle. It drafts; you check. Mitosis-vs-meiosis is the single thing AI gets wrong most here — catching it is the skill.

Come to class ready to look at a real onion-root-tip photo and argue about which cell is in which phase. See you Tuesday.

(B) Welcome Announcement — Module 9

Release setting: post on the module's start day (offset = 0 days), i.e., Tue Oct 27, 2026 — not before. If your platform won't preserve the scheduled date on import, post this as a draft labeled "Release: Tue Oct 27."

Subject: Welcome to Week 9 — how one cell becomes you 🔬

Hi everyone, and welcome back from the midterm!

Quick warm-up before we start: you began life as a single cell. You now have tens of trillions — and every single one was made by the same repeating process of one cell copying itself and splitting in two. That process is mitosis, and it's happening in your skin, your gut, and your bone marrow right now as you read this. This week we learn exactly how a cell copies itself precisely, billions of times, without losing its place — and what happens when the controls fail.

This week — The Cell Cycle & Mitosis — we tackle the big question: How does one cell become two identical cells, in a precise and controlled order, and how do we measure how fast it's happening? By Friday you'll lay out the cell cycle, put the four phases of mitosis in order (PMAT), tell a chromosome from a chromatid, and calculate a mitotic index from a real cell count.

Three things not to miss:
1. Lecture Tutorial 9 — work through the cell cycle, the PMAT order, and the mitotic-index math with one approved chatbot (Gemini, Claude, or ChatGPT) and submit the share link. Watch the model try to make mitosis produce four cells — and catch it. Due Sun Nov 1.
2. Lab 9 ("Counting Mitosis"), Quiz 9, Discussion 9, and Assignment 9 also close Sun Nov 1 — the lab uses a free virtual onion root tip where you count cells and compute the mitotic index, so start early.
3. Open the Start Here page first — it lays out everything in order with due dates.

One promise: this is a course about how living things work, not about memorizing a glossary. We'll keep leading with plain-language ideas. By Friday, the next time you hear that "cancer is uncontrolled cell growth," you'll know exactly what that means at the level of the cell cycle and its broken checkpoints.

Bring your curiosity (and a willingness to stare at onion cells) to class on Tuesday.

See you soon,
Prof. Castellano