The cell cycle and why cells divide

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. 1.

   Esme reads the wheel. Which job happens in the mitotic phase?

   • The cell grows, copies its DNA and divides, from start to finish
   • The cell grows and gathers energy before copying its DNA
   • The copied chromosomes are pulled apart and the cell splits
   • The cell copies its DNA so each chromosome has two chromatids

2. Read this first

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

   G1, S, G2, mitosis (M), cytokinesis.

3. 2.

   Jun walks clockwise around the wheel, starting at G1. Which list shows the segments in order?

   • Cytokinesis, mitosis, G2, S, G1
   • G1, G2, S, mitosis, cytokinesis
   • G1, S, G2, mitosis, cytokinesis
   • G1, S, G2, cytokinesis, mitosis
4. 3.

   Kira looks at the wheel. Which segment comes straight after S?

   • G2, the second gap
   • Mitosis, skipping the second gap
   • Cytokinesis, the cell splitting
   • G1, the first gap
5. 4.

   Luz brackets part of the wheel as interphase. Which segments belong in the bracket?

   • No segment: interphase is a rest between cycles
   • Mitosis alone, since mitosis is the whole cycle
   • G1, S and G2
   • Mitosis and cytokinesis

6. Four uses of cell division (facts from OpenStax Biology 2e)

   situation	what happens
   A	a sea urchin begins as 1 cell and has 16 cells after 4 rounds of cell division
   B	human epithelial cells are replaced after about 2 to 5 days on average
   C	a single-celled organism splits into 2 single-celled organisms
   D	a fertilized egg divides again and again until a person has trillions of cells

7. 5.

   Milo reads the card. Which situation shows cell division used for reproduction, not growth or replacement?

   • A: one cell becomes 16 cells in an animal
   • B: old epithelial cells are swapped for new ones
   • C: one cell becomes two new organisms
   • D: one cell becomes the many cells of a person
8. 6.

   Noah compares two cube cells. Which cell has more surface area for each unit of its volume?

   • The 3 µm cell, because bigger cells exchange materials better
   • Neither: both cubes share the same ratio
   • The 1 µm cell, with a ratio of 6
   • The 3 µm cell, since 54 is more surface area than 6
9. 7.

   A cube cell in Pia's model grows from a side of 2 µm to a side of 4 µm. What happens to its surface-area-to-volume ratio?

   • It stays at 3, since the cell keeps the same shape
   • It rises, since bigger cells exchange materials better
   • It falls from 3 to 1.5, so each part of the cell gets less membrane
   • It rises, since the bigger cell has more membrane
11. 8.

    At the G1 gate, Ren learns that a cell has damaged DNA. What happens next?

    • The cell goes on into S, since a gate cannot stop a cell
    • The cell goes straight to cytokinesis and splits
    • The cell is held at the gate while the damage is repaired
    • The cell skips ahead to mitosis
12. 9.

    Tala reads about the gate in mitosis. What must be true before the sister chromatids are pulled apart?

    Use the picture in question 8.

    • The DNA has been copied for the first time
    • Each pair of sister chromatids is attached to the spindle
    • The cell has already divided its cytoplasm
    • The cell has doubled in size
13. 10.

    “model, not to scale” Zee reads about a mature nerve cell that does not divide. Where is it in the cell cycle?

    • In G0, outside the active cycle
    • In G1, getting ready to divide again soon
    • In mitosis, stuck partway through dividing
    • In interphase, resting before its next division