How one cell becomes two (mitosis)

Grade 7 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Use this

   Two cards of a model animal cell, not to scale (model data: 4 chromosomes). Card P: the 4 chromosomes sit in a line across the middle of the cell. Card Q: the copies of each chromosome are pulled into two groups, with 4 moving toward each end.

2. 1.

   Noah's friend says the chromosomes are pulled apart in metaphase and line up in anaphase. Which response is best?

   • Disagree: they line up in metaphase and are pulled apart in anaphase
   • Disagree: they line up in prophase and are pulled apart in metaphase
   • Disagree: they line up in anaphase and are pulled apart in telophase
   • Agree: the pulling comes first, and then the chromosomes line up in the middle
3. 2.

   not to scale (model data: 4 chromosomes). Pia's friend says each new cell must get only half of the chromosomes, or the number would double with every division. Which response is best?

   • Agree: each new cell gets half, because a full set would double the number in each cell
   • Disagree: the chromosomes are not copied, so the new cells share the parent's set
   • Disagree: the chromosomes are copied first, so each new cell gets a full set
   • Agree: each new cell has to make up the missing half after the split
4. 3.

   not to scale (model data: 14 chromosomes). Bo reads cards S and Q of one dividing model cell. How many chromosomes will each new cell hold, and which stage is card S?

   • 28 chromosomes; metaphase
   • 7 chromosomes; metaphase
   • 14 chromosomes; metaphase
   • 14 chromosomes; anaphase

5. Use this

   Cards for one dividing model plant cell, not to scale (model data: 12 chromosomes). Card P: the 12 chromosomes are thin, tangled threads inside a round nucleus. Card Q: a new wall is forming across the middle of the cell, making two cells, and each has its own nucleus.

6. 4.

   Jun follows the model plant cell on cards P and Q through mitosis and cytokinesis. How many chromosomes are in the two new cells together?

   • 48
   • 36
   • 24
   • 12
7. 5.

   after it divided, not to scale (model data). Esme reads that mitosis made two new cells with 10 chromosomes each. How many chromosomes did the cell have before it divided?

   • 20
   • 10
   • 5
   • 15

8. Use this

   Notebook about one dividing model plant cell, model data. Line 1: In prophase, the chromosomes thicken and the nucleus boundary starts to break up. Line 2: In metaphase, the chromosomes line up across the middle. Line 3: In anaphase, the new wall is finished before the chromosomes reach the ends. Line 4: The two new cells have the same chromosomes as the first cell.

9. 6.

   Ari writes four notebook lines about a dividing plant cell. Which line has a flaw?

   • Line 3: the new wall forms after the chromosomes reach the ends
   • Line 2: the cell has already split in two by the time of metaphase
   • Line 1: the nucleus boundary stays whole until anaphase begins
   • Line 4: the new cells should hold half of the chromosomes of the first cell

10. Use this

    Notebook about what mitosis does, model data. Line 1: Root-tip cells divide by mitosis, and the new cells grow longer. Line 2: Gut-lining cells that wear off are replaced when nearby cells divide by mitosis. Line 3: Egg and sperm cells are made by mitosis, so they match the body cells. Line 4: The two new cells made by mitosis hold the same chromosomes as the first cell.

11. 7.

    Tala writes four notebook lines about what mitosis does. Which line has a flaw?

    • Line 2: nearby cells replace worn cells by growing bigger, not by dividing
    • Line 1: root-tip cells divide to make egg and sperm cells for the plant
    • Line 4: the two new cells should hold half of the first cell's chromosomes
    • Line 3: egg and sperm cells come from a different division, which halves the chromosomes

12. Use this

    Slide count (model data) for one root tip, 20 cells in all. Columns: Stage | Cells. In interphase | 17. In mitosis | 3.

13. 8.

    Luz's class counts 20 root-tip cells: 17 in interphase and 3 in mitosis. A classmate asks why so few are in mitosis. Which explanation fits?

    • Mitosis is short and interphase is long, so most cells are between divisions
    • Interphase is a resting time, so those 17 cells are idle until the root needs them
    • Interphase is the first stage of mitosis, so the 17 cells are in mitosis too
    • The root tip has stopped growing, so most of its cells have stopped dividing
14. 9.

    Each starting cell has 8 chromosomes. Ren sees that cell X's egg cells hold 4 chromosomes, but cell W's new cells hold 8. Does this break the rule that mitosis keeps the number?

    • Yes: mitosis sometimes halves the number of chromosomes, so the rule is wrong
    • Yes: mitosis halves the number when a cell is making egg cells for the animal
    • No: egg cells come from a different division that halves the number, and mitosis keeps 8
    • No: cell X copied its chromosomes twice before dividing, so it ended up with 4

15. Use this

    One card of a dividing model plant cell on a slide, not to scale (model data: 4 chromosomes). A new wall is just starting to form at the middle of the cell.

16. 10.

    Milo sees card Q: two nuclei in one plant cell, with a new wall just starting. A friend says the slide must be wrong. Which reply is best?

    • Yes: the cell must split as soon as the chromosomes are in two groups
    • Yes: each nucleus should hold 2 chromosomes, half of the 4
    • No: this is interphase, when the cell has copied its chromosomes
    • No: this is telophase, and cytokinesis finishes the division