When the cell cycle goes wrong: checkpoints and cancer

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Cycle wheel (model, not to scale), clockwise from the top

   G1, S, G2, mitosis (M), cytokinesis. Three gates (checkpoints) stand on the wheel: the G1 gate near the end of G1, the G2 gate before mitosis, and the M gate in mitosis, before the sister chromatids are pulled apart.

2. 1.

   Ari reads the wheel. Which gate checks that all the chromosomes have been copied before mitosis starts?

   • The M gate, in mitosis
   • The G1 gate, near the end of G1
   • No gate: the cell goes on whether or not the copying is finished
   • The G2 gate, before mitosis
3. 2.

   Bo reads the wheel. Before the cell moves on into S, what does the G1 gate check?

   • The cell's size and reserves, and whether its DNA is damaged
   • Nothing: the cell goes on into S whatever its condition
   • That each pair of sister chromatids is attached to the spindle
   • That the chromosomes have been copied

4. Regulator card (model)

   kind of regulator	job
   positive regulator	moves the cell on past a gate
   negative regulator	halts the cycle at a gate until a problem is fixed

5. 3.

   Jun reads the regulator card. Cyclins and Cdks are positive regulators. What is their job?

   • They split the cell's cytoplasm in two
   • They copy the DNA during S phase
   • They move the cell on past a gate
   • They halt the cycle until a problem is fixed
6. 4.

   Kira reads the regulator card. The protein p53 is a negative regulator. What does it do when DNA is damaged?

   • It halts the cycle so the DNA can be repaired
   • It copies the damaged DNA a second time
   • It splits the damaged cell in two
   • It pushes the cell on into S at once
7. 5.

   Luz reads the car-part card. In how it controls cell division, a tumor suppressor protein is like which car part?

   • The accelerator: it pushes cells to divide again and again
   • The brake: it keeps division in check
   • The steering wheel: it turns the cell toward new tissue
   • The fuel tank: it stores the energy for dividing

8. Use this

   model, not to scale. A gate drawn open lets a cell pass, a gate drawn closed holds the cell, and a gate drawn broken no longer checks.

9. 6.

   Milo reads the wheel. The G1 gate is closed and the cell's DNA is damaged. What is the gate doing?

   • Letting the cell into S, so the damage is copied
   • Holding the cell while the DNA is repaired
   • Broken, so the cell can no longer divide
   • Moving the cell on to mitosis
10. 7.

    Noah reads the wheel. The cell is in G2, its chromosomes are all copied and undamaged, and the G2 gate is open. What happens next?

    • The cell splits in two before mitosis begins
    • The cell is held at the gate while it copies more DNA
    • The cell goes back to G1 to start again
    • The cell passes the gate and enters mitosis

11. Use this

    Cycle wheel (model, not to scale), clockwise from the top: G1, S, G2, mitosis (M), cytokinesis. Three gates (checkpoints) stand on the wheel: the G1 gate near the end of G1, the G2 gate before mitosis, and the M gate in mitosis, before the sister chromatids are pulled apart. A gate drawn open lets a cell pass, a gate drawn closed holds the cell, and a gate drawn broken no longer checks. The G1 gate is drawn broken; the G2 gate and the M gate are drawn open. A cell at the G1 gate has damaged DNA and no working p53.

12. 8.

    Pia reads the wheel. The G1 gate is broken because p53 does not work, and the DNA is damaged. What does the cell do?

    • It stays at G1, because the gate still holds it
    • It stops dividing for good, because a broken gate halts the cell
    • It skips S and goes straight to mitosis
    • It goes on into S, because the gate no longer checks

13. Cells in a dish where every cell divides each round (model data)

    round	cells in the dish
    0	1
    1	2
    2	4
    3	8
    4	16
    5	32

    Every cell divides once in each round.

14. 9.

    Tala reads the table. In which round does the dish first hold 32 cells?

    • Round 5
    • Round 4
    • Round 3
    • Round 6
15. 10.

    Zee reads the table. What happens to the number of cells in each round?

    • It goes up by 2 cells
    • It doubles
    • It stays the same
    • It halves