Answer the following questions in complete sentences in the space provided: 1. Why does cell division take place in single-celled organisms?

2. What occurs in a cell when it is not undergoing cell division?

3. How do chromosomes change before cell division?

4. What is mitosis?

5. Why doesn’t mitosis occur in prokaryotes?

6. What would happen if DNA did not duplicate during interphase?

7. What is cytokinesis and when does it happen?

8. During what phase of mitosis do the chromosomes line up?

9. When do the chromosomes condense and become visible under a microscope? 10. What happens to the chromosomes during anaphase?

11. Sometimes a cell inaccurately duplicated its DNA, and the resulting cells are not identical. What effects might such a change have on the organism?

1.All multicellular organisms use cell division for growth and the maintenance and repair of cells and tissues. Cell division is tightly regulated because the occasional failure of regulation can have life-threatening consequences. Single-celled organisms use cell division as their method of reproduction.

2.What happens to cells that "decide" not to divide? If the decision is to not divide, the cell goes into a quiescent, or nondividing state, called G0 (G zero).

3.Prophase is the first phase of mitosis. During this phase, the chromosomes inside the cell's nucleus condense and form tight structures. In fact, the chromosomes become so dense that they appear as curvy, dark lines when viewed under a microscope (Figure 1).

4.Mitosis is a process where a single cell divides into two identical daughter cells (cell division).

5.In bacterial cells, the genome consists of a single, circular DNA chromosome; therefore, the process of cell division is simplified. Mitosis is unnecessary because there is no nucleus or multiple chromosomes. This type of cell division is called binary fission.

6.If a cell has not properly copied its chromosomes or there is damage to the DNA, the CDK will not activate the S phase cyclin and the cell will not progress to the G2 phase. The cell will remain in S phase until the chromosomes are properly copied, or the cell will undergo programmed cell death.

7.Cytokinesisis the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and meiosis.

8.Metaphase. Chromosomes line up at the metaphase plate, under tension from the mitotic spindle. The two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles. In metaphase, the spindle has captured all the chromosomes and lined them up at the middle of the cell, ready to divide.

9.During prophase, the complex of DNA and proteins contained in the nucleus, known as chromatin, condenses. The chromatin coils and becomes increasingly compact, resulting in the formation of visible chromosomes.

11.When Replication Errors Become Mutations. Incorrectly paired nucleotides that still remain following mismatch repair become permanent mutations after the next cell division. This is because once such mistakes are established, the cell no longer recognizes them as errors.