Biology Chapter 12 Homework Answers

Chapter 12, The Cell Cycle

1. Describe how are the three subphases of interphase are alike and how they are different.

– They are alike in that many of the cell’s metabolic processes occur in all three.

– They are different by if the DNA has not replicated (G1), is replicating (S) or has already

replicated (G2). The checkpoints are also different in each of phase.

2. Is binary fission the same as mitosis? Explain.

– Binary fission is the division of a prokaryotic cell which lacks a nucleus.

– Mitosis is the division of the nucleus of a eukaryotic cell. They are not the same thing.

3. During prometaphase, the nuclear envelope disappears. Where does it go?

– The components of the nuclear envelope are in the cytoplasm.

4. Imagine a cell that mutates and loses the function of its kinetochore proteins. Explain what

this might do to the cell the next time it divides.

– The kinetochores could not pull the replicated chromatids apart after the centromere

breaks. The chromosomes would stay together and the chromosome number would likely

double with each replication.

5. Is mitosis the same thing as Cytokinesis? Explain.

– No.

– Mitosis is the division of the nucleus while cytokinesis is the division of the cytoplasm.

6. Imagine another cell mutation that allows the cell to ignore anchorage dependency. Discuss

what might be the results of this mutation.

– The cells might divide and travel off. This is what happens when cancer undergoes

metastasis and spreads through the body.

7. Identify where in the cell cycle the three main checkpoints are located. What determines if the

cell moves past each checkpoint?

½ pt name, ½ pt event, 3 pts total

G1 checkpoint – cell must receive a go-ahead signal or exit into Go

G2 checkpoint – requires MPF activity to go-ahead to mitosis

M checkpoint – controls the onset of anaphase.

8. Chemicals, such as colchicine from the Autumn Crocus plant, are known to disrupt

spindle fibers. Speculate on what affect this will have on a cell undergoing mitosis.

Identify what ploidy level (N=?) of the cell resulting from this treatment.

– The spindle fibers will not form during mitosis and the chromatids cannot be pulled

apart.

– This tends to double the chromosome number (tetraploid).

9. Imagine that the enzyme that breaks down cyclin is on strike and refuses to work. Explain

what might be result from this situation.

– Cyclin would remain and active MPF would be constantly present. This would signal

the cell to continually divide.

10. Small cuts that open blood vessels and bleed often heal faster than cuts that don’t

bleed (e.g. paper cuts). Using your knowledge of factors that affect cell division,

speculate on a possible mechanism for why this occurs.

– Bleeding brings platelets to the area to form blood clots. The presence of platelets places

the cell division stimulate PDGF in the cut. PDGF would stimulate cell division and

close the wound faster.

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