7^th Grade Science Mitosis Name: ___________________

1. The proper name for cell division is : ___________________________

2. List three reasons cells divide:

3. Which tend to divide fastest under favorable conditions?

a) Algae b) Intestinal cells c) Hydras d) Bacteria

4. List in order the four stages of cell division:

5. Which organ replaces its cells with mitotic divisions?

a) Intestine b) Skin c) Brain d) All of these

6. During which stage of cell division do the chromosomes become visible first?

a) Metaphase b) Prophase c) Telophase d) Anaphase

7. What is NOT visible during the first early stages of mitosis?

a) Chromosomes b) Cell membrane c) Nucleus d) Spindles

8. Stage of mitosis when all the chromosomes line up in the middle:

a) Metaphase b) Prophase c) Telophase d) Anaphase

9. When is DNA replicated?

a) Before mitosis begins b) When the chromosomes are visible

c) When the chromosomes line up d) After chromosomes are separated

10. Reformation of the nuclei and pinching apart of cell membranes signal the end of:

a) Metaphase b) Prophase c) Telophase d) Anaphase

11. In order for a cell to divide: a) its DNA is copied b) the nucleus dissolves

c) chromosomes separate d) all of these

12. Which organism reproduces by mitosis?

a) humans b) bacteria c) elephants d) tigers

13. Skin cells are replaced how often (from the new dermis to outer epidermis)?

a) every month b) yearly c) daily d) never

14. What did we attempt to view in the lab this week?
Chromosome Alignment in Mitosis

Microtubules, formed in prophase and also known as spindles, have already found and attached themselves to kinetochores in metaphase. The centromeres of the chromosomes convene themselves on the metaphase plate, an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores, analogous to a tug of war between equally strong people. In certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the midline.

Early events of metaphase can coincide with the later events of prophase, as chromosomes with connected kinetochores will start the events of metaphase individually before other chromosomes with unconnected kinetochores that are still lingering in the events of prophase.

One of the cell cycle "checkpoints" occurs during prophase and metaphase. Only after all chromosomes have become aligned at the metaphase plate, when every kinetochore is properly attached to a bundle of microtubules, does the cell enter anaphase. It is thought that unattached or improperly kinetochores generate a signal to prevent premature progression to anaphase, even if most of the kinetochores have been attached and most of the chromosomes have been aligned. This would be accomplished by regulation of the Anaphase Promoting Complex, securin, and separase.

15. What is this article about?

16. Centromeres are parts of:

a) chromosomes b) kinetochores c) cell walls d) none of these

17. What is the likelihood you have chromosomes in your body right now?

a) Very high b) Not likely c) Nothing like this exists in a human

18. What is the likelihood you have kinetochores in your body right now?

a) Very high b) Not likely c) Nothing like this exists in a human

19. What event signals the start of Anaphase?

20. What is another name for spindles?