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 swaps its DNA for new DNA that fits the job
   • 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

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?

   • 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
   • Different DNA, because their shapes are different

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

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

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

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

    • 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
    • No, cells of the same width must have different DNA

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?

    • Just the muscle cell's nucleus holds DNA
    • Both cells use their whole set of genes at once
    • Each cell has its own DNA, matching its job
    • It is the same set of DNA instructions in both
13. 8.

    model, not to scale. Pia says every body cell has a nucleus full of DNA. Which drawn cell is an exception?

    • Cell D, the disc-shaped cell
    • Cell C, the branching cell
    • Cell B, the long striped cell
    • Cell A, the flat cell

14. 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.

15. 9.

    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
    • Adults have stem cells too, such as the ones in bone marrow
    • Adults lose their stem cells; young children keep theirs
    • Bone marrow cells are already specialized and cannot divide
16. 10.

    The front reads: apical meristem. The back is blank. Zee wants to find a plant's apical meristems. Where should the search start?

    • Along the sides of stems, where the plant thickens
    • Nowhere; plants get longer as existing cells stretch
    • At the tips of the shoots and the roots
    • In the leaves, where sugars are made