The cell cycle and why cells divide

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

2. 1.

   Ari reads the cell cycle wheel. In which segment is the cell's DNA copied?

   • The S segment
   • The cytokinesis segment
   • The mitosis segment
   • The G1 segment
3. 2.

   Bo watches a new cell form. It is growing and gathering building blocks, and its DNA is not copied yet. Which part of the wheel is it in?

   Use the picture in question 1.

   • No segment: a new cell rests before the cycle starts
   • M, the mitotic phase
   • G2, the second gap
   • G1, the first gap
4. 3.

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

   Use the picture in question 1.

   • The cell copies its DNA so each chromosome has two chromatids
   • The copied chromosomes are pulled apart and the cell splits
   • The cell grows and gathers energy before copying its DNA
   • The cell grows, copies its DNA and divides, from start to finish
5. 4.

   G1, S, G2, mitosis (M), cytokinesis. Jun walks clockwise around the wheel, starting at G1. Which list shows the segments in order?

   • G1, S, G2, mitosis, cytokinesis
   • G1, S, G2, cytokinesis, mitosis
   • G1, G2, S, mitosis, cytokinesis
   • Cytokinesis, mitosis, G2, S, G1

6. Read this first

   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?

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

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

   • The 1 µm cell, with a ratio of 6
   • Neither: both cubes share the same ratio
   • The 3 µm cell, because bigger cells exchange materials better
   • 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 rises, since the bigger cell has more membrane
   • It falls from 3 to 1.5, so each part of the cell gets less membrane
   • It stays at 3, since the cell keeps the same shape
   • It rises, since bigger cells exchange materials better
11. 8.

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

    • The cell is held at the gate while the damage is repaired
    • The cell goes straight to cytokinesis and splits
    • The cell skips ahead to mitosis
    • The cell goes on into S, since a gate cannot stop a cell
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 doubled in size
    • The cell has already divided its cytoplasm
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 mitosis, stuck partway through dividing
    • In G1, getting ready to divide again soon
    • In interphase, resting before its next division