学习 · 生物学

Cell Cycle & Mitosis: How One Cell Becomes Two

The CBE tests both the cell cycle macro-phases (G1/S/G2/M) and the mitosis substages (Prophase, Metaphase, Anaphase, Telophase). Master both levels and how they connect.

9 分钟 TEKS 5B,5C 生物学

Two levels — don't confuse them

Texas Biology CBE asks two different kinds of cell-division questions, and they live at different scales:

  1. Cell cycle (the macro view): a single cell’s entire life, divided into G1 → S → G2 → M.
  2. Mitosis (the micro view): just the M phase, broken into Prophase → Metaphase → Anaphase → Telophase.

If a question says “During which phase of the cell cycle…”, the answer is one of G1 / S / G2 / M. If it says “Which stage of mitosis…”, the answer is one of Prophase / Metaphase / Anaphase / Telophase. Mixing these up loses easy points.

The cell cycle clock

The four phases. Memorize what each one does — the diagram won't tell you.
The four phases. Memorize what each one does — the diagram won't tell you.
What happens in each phase
  • G1 (Growth 1) — cell grows, makes proteins, organelles double. Longest phase.
  • S (Synthesis) — DNA replicates. Each chromosome doubles into two sister chromatids.
  • G2 (Growth 2) — cell prepares for division: makes mitotic proteins, checks DNA.
  • M (Mitosis + cytokinesis) — the cell physically divides into two identical daughter cells.

Famous CBE question: “During which phase does DNA replication occur?” — the answer is S phase, not M. M is when the already-doubled DNA gets divided up, not when it’s copied.

The four stages of mitosis (M phase)

Once the cell enters M phase, it goes through four substages. Each one has a signature look:

The four stages of mitosis in chronological order. Memorize the visual signature of each — that's how the exam will test you.
The four stages of mitosis in chronological order. Memorize the visual signature of each — that's how the exam will test you.
Prophase (P): chromosomes condense and become visible. Nuclear envelope breaks down. Spindle fibers form.
Metaphase (M): chromosomes line up at the middle (metaphase plate). Mnemonic: M = Middle.
Anaphase (A): chromosomes split apart; sister chromatids pulled to opposite poles. A = Apart.
Telophase (T): nuclear envelopes re-form around the two new sets. Cytokinesis pinches the cell into two.
Memory mnemonic
“Please Make A Tuesday” — Prophase, Metaphase, Anaphase, Telophase. The order is alphabetical-ish; just memorize that M comes after P, not before.

What does mitosis produce?

Mitosis takes one cell and produces two identical diploid daughter cells. The genetic material is split equally — both daughters get the same number of chromosomes the parent had, with the same DNA. Mitosis is used for growth, repair, and asexual reproduction.

Don’t confuse it with meiosis (lesson 4), which makes four haploid gametes for sexual reproduction.

Check yourself

Quick check #1
During which phase of the cell cycle is DNA replicated?
Quick check #2
Which stage of mitosis is shown when chromosomes are lined up in a single row at the cell's equator?

Practice with real CBE questions