The cell cycle and why cells divide
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Read this first
Onion root tip counts from a slide (model data)
stage cells counted interphase 170 mitosis 24 cytokinesis 6 In all, 200 cells were counted, and one full cycle takes 20 hours.
Ari estimates time from the slide: cells in a stage ÷ total cells × cycle time. About how many hours of the cycle are spent in interphase?
- 17 hours
- 8.5 hours
- 2.4 hours, because mitosis is the whole cycle
- 0 hours, because interphase is a rest and is not counted
Bo uses the same slide. About how long does the mitotic phase, mitosis plus cytokinesis, last?
- 15 hours
- 3 hours
- 17 hours
- 2.4 hours
Esme says cytokinesis takes longer than mitosis because it comes last. Does the slide support this?
- No: the two last equally long, since both are in the mitotic phase
- Yes: 6 cells is the shorter count, so that stage lasts longer
- No: 24 mitosis cells to 6 cytokinesis cells means mitosis lasts about 4 times as long
- Yes: the stage that comes last takes the longest
Cycle wheel (model, not to scale), clockwise from the top
G1, S, G2, mitosis (M), cytokinesis. A model cell has 10 chromosomes in G1 (model data). The cell then goes once around the wheel.
Jun follows the model cell. How many chromatids does it have at the end of G2, and how many chromosomes does each daughter cell have?
- 20 chromatids; 5 chromosomes in each daughter
- 20 chromatids; 10 chromosomes in each daughter
- 20 chromatids; 20 chromosomes in each daughter
- 10 chromatids; 10 chromosomes in each daughter
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 is in the middle of mitosis: its sister chromatids have just been pulled to opposite ends, each now counted as a chromosome, and the cell has not yet split.
Kira looks at the drawn cell, which has not split yet. How many chromosomes are in the whole cell now, and how many gather at each end?
- 92 in the cell, 92 at each end
- 46 in the cell, 46 at each end
- 46 in the cell, 23 at each end
- 92 in the cell, 46 at each end
Luz says DNA is copied during mitosis. Which reading of the graph shows this is wrong?
- DNA per cell drops at hour 20 because half of it is used up in mitosis
- DNA per cell is 4 units during mitosis, so the copying must happen then
- DNA per cell has already reached 4 units by hour 16, before mitosis starts at hour 19
- At hour 20 each daughter has 4 units, double the parent's 2 at hour 0
Use this
Notebook (model data), 4 rows. Columns: line, what it says. 1, A human body cell has 46 chromosomes in G1. 2, After S, it still has 46 chromosomes, now 92 chromatids. 3, Each daughter cell gets 92 chromosomes. 4, Cytokinesis comes after the chromosomes are sorted into two groups.
Pia proofreads a notebook about chromosome counts. Exactly one line is wrong. Which line, and why?
- Line 2, because copying the DNA makes 92 chromosomes
- Line 3, because each daughter gets 46, the same as the parent
- Line 1, because a human body cell has 23 chromosomes
- Line 4, because cytokinesis happens before the chromosomes are sorted
Card (real data, from OpenStax Biology 2e)
kind of cell cell turnover early human embryo cell a few hours epithelial cell 2 to 5 days on average cortical neuron (a nerve cell) a whole lifetime spent in G0 Ren writes: body cells keep dividing, so a mature nerve cell must divide often. Does the card support this?
- No: a nerve cell spends its lifetime in G0 and does not divide
- Yes: cells that are not dividing are resting in interphase
- No: a nerve cell divides within a few hours, like an embryo cell
- Yes: cells keep dividing, so a nerve cell just takes longer
Tala claims the 60 µm cell exchanges materials better because it has 9 times the surface area. Is the claim sound?
- No: its volume is 27 times larger, so its ratio is lower, 0.1 against 0.3
- Yes: more surface area means more membrane to exchange through
- Yes: a larger cell has a higher ratio because both numbers grow
- No: both cells have the same ratio, since both are cubes
Fruit fly early embryo (real data, from OpenStax Biology 2e)
what happens when one cell cycle takes about 8 minutes the nucleus divides many times by mitosis first cytokinesis happens once the cell has many nuclei Zee claims cytokinesis must come before mitosis. In a fruit fly embryo's early cycles, the nucleus divides many times before the cell splits. Does this support the claim?
- No: here mitosis runs many times first, and the cell splits later
- Yes: the cell must split before it can copy its DNA
- Yes: cytokinesis comes first, so the cell can then divide its nucleus
- No: mitosis and cytokinesis happen at the same moment