The cell cycle and why cells divide
Grade 9 Science Worksheet
Circle the best answer.
Read this first
Cycle wheel (model, not to scale), clockwise from the top
G1, S, G2, mitosis (M), cytokinesis. A human body cell has 46 chromosomes in G1. The drawn cell sits in the G2 segment: its nucleus shows each chromosome as an X of two joined sister chromatids.
Ari studies a human body cell drawn in G2. How many chromosomes and how many chromatids are in its nucleus?
- 92 chromosomes, 46 chromatids
- 92 chromosomes, 92 chromatids
- 46 chromosomes, 46 chromatids
- 46 chromosomes, 92 chromatids
“Cycle wheel (model, not to scale), clockwise from the top:” Bo follows a human body cell with 46 chromosomes as it copies its DNA and divides in two. How many chromosomes in each daughter, and in the two together?
- 46 each, 92 together
- 46 each, 46 together
- 92 each, 184 together
- 23 each, 46 together
Use this
Count table (model data), 4 rows. Columns: where in the cycle, chromosomes, chromatids. A cell in G1: 8, 8. The same cell after S: 8, 16. The same cell just before it divides: 8, 16. One daughter cell just after cytokinesis: ____, ____.
Esme completes the count table for a model organism. Which numbers go in the last row?
- 4 chromosomes, 4 chromatids
- 8 chromosomes, 8 chromatids
- 8 chromosomes, 16 chromatids
- 16 chromosomes, 16 chromatids
Use this
Cycle wheel (real data from OpenStax Biology 2e: human cells dividing rapidly in a lab dish), 24 hours around.
Jun reads the wheel. Which phase takes the largest share of the 24 hours, and about what percent?
- S, about 10 percent
- S, about 42 percent
- M, since dividing is the main event of the cycle
- G1, about 38 percent
Kira adds up interphase on the same wheel. How long is interphase, and what percent of the cycle is it?
Use the picture in question 4.
- 0 hours: interphase is a rest, so it is not counted
- 19 hours, about 79 percent
- 23.5 hours, about 98 percent
- 0.5 hours: mitosis is the cell cycle, so interphase is not counted
Luz claims a dividing cell spends most of its time in mitosis. What do the wheel's numbers show?
Use the picture in question 4.
- The claim is wrong: M is about 2 percent and the rest is interphase
- The claim is wrong: M is about 50 percent of the cycle
- The claim is right: interphase is a rest, so just M counts as active time
- The claim is right: mitosis is the biggest part of the cycle
Milo reads the table. Which statement does it support?
- The 10 µm cell has the higher ratio, because its surface area of 600 is larger
- The 10 µm cell exchanges materials better, because 600 is more surface area than 150
- The 10 µm cell has 4 times the area and 8 times the volume, so a lower ratio
- Both cells share one ratio, because both are cubes with the same shape
Noah's cube cell grows from a side of 4 µm to 8 µm. Which sentence best explains why growing cells divide?
- Dividing makes surface area fall to match volume, so the ratio stays the same
- A bigger cell has more membrane, so it exchanges better and has no need to divide
- A bigger cell has too much surface area for its organelles to use
- Volume rises faster than surface area, so a big cell has less membrane for its volume
At the G2 gate, Ren learns that some chromosomes were not fully copied. What does the cell do?
- It enters mitosis, where the copying is finished
- It skips to cytokinesis and splits first
- It passes, because the M gate repairs missing copies
- It is held at the gate while it finishes copying or repairs the DNA
At the gate in mitosis, Tala sees one pair of sister chromatids attached to spindle fibers from only one pole. What happens?
Use the picture in question 9.
- The cell waits, since pulling chromatids apart cannot be undone
- The chromatids separate anyway; cells keep dividing once started
- The cell goes back to S to copy the DNA again
- The cell divides its cytoplasm first, then sorts the chromosomes