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 swaps its DNA for new DNA that fits the job
   • The cell leaves the cycle and becomes specialized, with a shape for its job
   • The cell copies its DNA again and divides into two identical cells

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
   • Different DNA, because their shapes are different
   • 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 cells divide, and some of the new cells specialize, such as into xylem
   • Its cells keep their first shape, so no new tissues form
   • Its specialized cells divide into any other kind of plant cell
   • 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?

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

   • Covering a surface as a thin sheet
   • Receiving and sending signals
   • Contracting to move the body
   • 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
    • Size is one clue, but shape and features also show a cell's job
    • Yes, cells of the same width do the same 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?

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

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 uses both genes, since it holds both
    • The cell uses the hemoglobin gene; the myosin gene stays in its DNA, unused
    • The cell has the hemoglobin gene but lost the myosin gene
    • The cell copied the hemoglobin gene into a new cell
15. 9.

    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 B, the long striped cell
    • Cell A, the flat cell
    • Cell C, the branching cell
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?

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