How one cell becomes two (mitosis)

Grade 7 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Two cards of a model animal cell, not to scale (model data: 4 chromosomes). Zee's friend says interphase is the first stage of mitosis, because the chromosomes are copied then. Which response is best?

   • Agree: copying the chromosomes is how mitosis starts, so interphase is its first stage
   • Disagree: interphase comes before mitosis, when the cell grows and copies its chromosomes
   • Agree: interphase is a quiet resting time, so it is the first stage of mitosis
   • Disagree: the chromosomes are copied in prophase, not in interphase

2. 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.

3. 2.

   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 anaphase and are pulled apart in telophase
   • Disagree: they line up in prophase and are pulled apart in metaphase
   • Agree: the pulling comes first, and then the chromosomes line up in the middle
4. 3.

   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 has to make up the missing half after the split
   • Disagree: the chromosomes are not copied, so the new cells share the parent's set
   • Agree: each new cell gets half, because a full set would double the number in each cell
   • Disagree: the chromosomes are copied first, so each new cell gets a full set
5. 4.

   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?

   • 14 chromosomes; metaphase
   • 14 chromosomes; anaphase
   • 7 chromosomes; metaphase
   • 28 chromosomes; metaphase
6. 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?

   • 5
   • 10
   • 20
   • 15

7. Use this

   Notebook about one model animal cell that starts with 4 chromosomes, model data. Line 1: In interphase, the cell grows and copies its chromosomes. Line 2: In metaphase, the chromosomes line up across the middle. Line 3: In anaphase, the copies are pulled apart, with 4 moving toward each end. Line 4: After cytokinesis, there are 2 cells with 2 chromosomes each.

8. 6.

   Kira writes four notebook lines about a model cell that starts with 4 chromosomes. Which line has a flaw?

   • Line 2: the chromosomes line up in anaphase, not in metaphase
   • Line 1: the cell copies its chromosomes in prophase, not in interphase
   • Line 3: 2 chromosomes, not 4, should move toward each end
   • Line 4: each new cell should have 4 chromosomes, not 2

9. 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.

10. 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 3: egg and sperm cells come from a different division, which halves the chromosomes
    • Line 4: the two new cells should hold half of the first cell's chromosomes
    • Line 1: root-tip cells divide to make egg and sperm cells for the plant

11. Use this

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

12. 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?

    • Interphase is the first stage of mitosis, so the 17 cells are in mitosis too
    • Interphase is a resting time, so those 17 cells are idle until the root needs them
    • The root tip has stopped growing, so most of its cells have stopped dividing
    • Mitosis is short and interphase is long, so most cells are between divisions
13. 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 halves the number when a cell is making egg cells for the animal
    • No: cell X copied its chromosomes twice before dividing, so it ended up with 4
    • Yes: mitosis sometimes halves the number of chromosomes, so the rule is wrong
    • No: egg cells come from a different division that halves the number, and mitosis keeps 8

14. 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.

15. 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: 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
    • Yes: the cell must split as soon as the chromosomes are in two groups