How cells specialize, and what stem cells are

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Cycle wheel (model, not to scale), clockwise from the top

   G1, S, G2, mitosis (M), cytokinesis. A side branch labeled G0 leaves the wheel near the start of G1. A branch leaves the wheel at G0 and ends at a drawn cell A. Cell A has a round body with a nucleus, branching projections and one long projection.

2. 1.

   Ari follows a side branch from the wheel to cell A. What does taking this branch show?

   • The cell stays ready to divide into any other kind of cell
   • The cell copies its DNA again and divides into two identical cells
   • The cell leaves the cycle and becomes specialized, with a shape for its job
   • The cell swaps its DNA for new DNA that fits the job

3. Cycle wheel (model, not to scale), clockwise from the top

   G1, S, G2, mitosis (M), cytokinesis. A side branch labeled G0 leaves the wheel near the start of G1. Two branches leave the wheel after G1. Branch A ends at a flat, round cell A with a small nucleus in the middle. Branch B ends at a tall, narrow cell B with its nucleus near the bottom end.

4. 2.

   Bo compares cells A and B, which both came from one G1 cell. What do the nuclei of A and B share?

   • Different DNA, because their shapes are different
   • The same genes switched on, so they do the same job
   • The same DNA, copied from the cell they both came from
   • The same shape, because both started as one cell

5. Cycle wheel (model, not to scale), clockwise from the top

   G1, S, G2, mitosis (M), cytokinesis. A side branch labeled G0 leaves the wheel near the start of G1. The wheel is a dividing cell in a root tip. A branch leaves the wheel after G1 and ends at a drawn cell A that carries water and minerals up the plant.

6. 3.

   Esme reads a wheel for a cell in a root tip. A branch leads to cell A, which carries water up the plant. What does the root tip do?

   • Its specialized cells divide into any other kind of plant cell
   • Its cells keep their first shape, so no new tissues form
   • Its cells divide, and some of the new cells specialize, such as into xylem
   • It makes no new cells, because plants have no cells that divide and specialize
7. 4.

   “Drawn cell (model, not to scale):” Jun studies a drawn cell that is long and striped, with many nuclei along its edge. Which job fits this cell?

   • Carrying oxygen to tissues
   • Contracting to move the body
   • Sending signals, since any long cell is a nerve cell
   • Covering a surface as a thin sheet

8. Use this

   Drawn cell (model, not to scale): a round cell body with a nucleus in the middle, several short branching projections on one side, and one long projection on the other.

9. 5.

   Kira studies a drawn cell with a round body, branching projections on one side and one long projection. Which job fits?

   • Receiving and sending signals
   • Contracting to move the body
   • Covering a surface as a thin sheet
   • Carrying oxygen to tissues
10. 6.

    Luz says cells A and B do the same job because both are 8 µm wide. What is the best reply?

    • No, cells of the same width must have different DNA
    • Yes, cells of the same width do the same job
    • Size is one clue, but shape and features also show a cell's job
    • Yes, a nucleus in the cell means the same job

11. Two body cells (model data)

    cell	has a nucleus
    nerve cell	yes
    muscle cell	yes

12. 7.

    Milo learns that a nerve cell and a muscle cell from one person each have a nucleus. What is true of the DNA in their nuclei?

    • Each cell has its own DNA, matching its job
    • Just the muscle cell's nucleus holds DNA
    • It is the same set of DNA instructions in both
    • Both cells use their whole set of genes at once

13. One cell's genes (model data)

    gene	state in this cell
    gene for hemoglobin	on
    gene for myosin	off

14. 8.

    Noah reads that the hemoglobin gene is on and the myosin gene is off in a cell. What does that mean?

    • The cell has the hemoglobin gene but lost the myosin gene
    • The cell copied the hemoglobin gene into a new cell
    • The cell uses both genes, since it holds both
    • The cell uses the hemoglobin gene; the myosin gene stays in its DNA, unused

15. Flash card (not to scale)

    The front reads: an unspecialized cell that can divide to make more of itself and can also give rise to specialized cells. The back is blank.

16. 9.

    Ren reads a card about a cell that is unspecialized, can divide, and can give rise to specialized cells. What is it?

    • A stem cell, which can divide and can also specialize
    • A childhood cell, which adults no longer have
    • A muscle cell, which is already specialized to contract
    • A specialized cell, which can divide into any other cell type

17. Flash card (not to scale)

    The front reads: adult bone marrow holds stem cells that make platelets, red blood cells and white blood cells. The back is blank.

18. 10.

    Tala says only young children have stem cells. A card says adult bone marrow holds stem cells that make blood cells. What is true?

    • Adult stem cells exist but cannot give rise to other cells
    • Bone marrow cells are already specialized and cannot divide
    • Adults have stem cells too, such as the ones in bone marrow
    • Adults lose their stem cells; young children keep theirs