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Checkpoints & the Cell Cycle: Reflection-and-Repair Worksheet

Cells divide a lot—yet most of the time they still copy and pass on DNA reliably. How? They don’t just “go go go.” They pause, check, and only then move forward.

1) Summary Frame (Fill in the blanks)

Complete the frame by writing the missing key terms in the blanks.

1. The cell cycle is commonly described as _____ (G1), _____ (S), _____ (G2), and _____ (M), which together help a cell grow, copy DNA, and divide.
2. During _____ (G1), the cell mainly grows and gets supplies ready; during _____ (S), it copies its DNA so each new cell can inherit a full set.
3. During _____ (G2), the cell double-checks that DNA copying finished correctly and prepares the machinery needed for division.
4. In _____ (M), the cell separates copied chromosomes and splits into two cells.
5. The timing of these stages is controlled by molecular “green lights” called _____ (cyclin/CDK), which push the cell forward only when conditions are right.
6. The _____ (G1/S checkpoint) helps prevent the cell from copying damaged DNA, while the _____ (G2/M checkpoint) helps prevent a cell from dividing before DNA is fully and accurately copied.
7. The _____ (spindle checkpoint) makes sure chromosomes are properly attached to the spindle so they get pulled apart evenly.
8. If these safeguards fail, cells may end up with the wrong number of chromosomes, a problem called _____ (aneuploidy).

2) Common Misconceptions (Repair these in your own words)

Rewrite each statement so it becomes accurate.

• “Checkpoints are extra steps the cell can skip if it’s in a hurry.”
• “Cyclins and CDKs are only important during mitosis (M phase).”
• “The G1/S checkpoint checks whether chromosomes are lined up in the middle of the cell.”
• “Aneuploidy means the DNA sequence has a small mutation in one gene.”

3) Final Prompt: Heredity Across Divisions

Explain how checkpoints (G1/S, G2/M, and the spindle checkpoint) help support heredity—the reliable passing of genetic information from one cell generation to the next—across many rounds of cell division.

Takeaway

Cell division isn’t just fast—it’s careful. Checkpoints act like quality-control gates so DNA gets copied and separated in a way that keeps genetic information stable across generations of cells.