Biology 1406 - Chapter 12

1. If there are 20 chromatids in a cell, how many centromeres are there?

10

20

40

5

In a cell, each chromatid has one centromere. Since there are 20 chromatids, there must be 20 centromeres. Therefore, the correct answer is 20.

Explanation

In a cell, each chromatid has one centromere. Since there are 20 chromatids, there must be 20 centromeres. Therefore, the correct answer is 20.

2. Chromosomes first become visible during which phase of mitosis?

Metaphase

Telophase

Anaphase

Prophase

During prophase, the chromosomes condense and become visible under a microscope. This is because the chromatin fibers, which are loosely packed in interphase, start to coil and condense into tightly packed chromosomes. The nuclear envelope also begins to break down during prophase, allowing the chromosomes to be more easily observed. Therefore, prophase is the phase of mitosis when chromosomes first become visible.

Explanation

During prophase, the chromosomes condense and become visible under a microscope. This is because the chromatin fibers, which are loosely packed in interphase, start to coil and condense into tightly packed chromosomes. The nuclear envelope also begins to break down during prophase, allowing the chromosomes to be more easily observed. Therefore, prophase is the phase of mitosis when chromosomes first become visible.

3. Starting with a fertilized egg, a series of five cell divisions would produce in early embryo with how many cells?

4

8

16

32

Starting with a fertilized egg, each cell division doubles the number of cells. Therefore, after five cell divisions, there would be a total of 32 cells.

Explanation

Starting with a fertilized egg, each cell division doubles the number of cells. Therefore, after five cell divisions, there would be a total of 32 cells.

4. Why do chromosomes coil during mitosis?

To increase their potential energy.

To allow chromosomes to move without becoming entangled and breaking

To allow chromosomes to fit within the nuclear envelope

To allow the sister chromatids to remain attached.

During mitosis, chromosomes coil to allow them to move without becoming entangled and breaking. This coiling helps to compact the DNA into a more condensed structure, making it easier for the chromosomes to separate and move to opposite ends of the cell. If the chromosomes were not coiled, they would be more likely to become tangled with each other, leading to potential breakage and errors in the distribution of genetic material. Coiling also helps to protect the DNA from damage during the process of cell division.

Explanation

During mitosis, chromosomes coil to allow them to move without becoming entangled and breaking. This coiling helps to compact the DNA into a more condensed structure, making it easier for the chromosomes to separate and move to opposite ends of the cell. If the chromosomes were not coiled, they would be more likely to become tangled with each other, leading to potential breakage and errors in the distribution of genetic material. Coiling also helps to protect the DNA from damage during the process of cell division.

5. Nerve and muscle cells are in _________ phase.

G0

G1

S

Mitotic

Nerve and muscle cells are in the G0 phase. The G0 phase is a resting or non-dividing phase in the cell cycle where cells temporarily or permanently exit the cell cycle. In this phase, cells do not actively replicate their DNA or divide. Nerve and muscle cells, once they have reached their fully differentiated state, typically remain in the G0 phase and do not undergo further cell division. This allows them to perform their specialized functions without the need for continuous cell division.

Explanation

Nerve and muscle cells are in the G0 phase. The G0 phase is a resting or non-dividing phase in the cell cycle where cells temporarily or permanently exit the cell cycle. In this phase, cells do not actively replicate their DNA or divide. Nerve and muscle cells, once they have reached their fully differentiated state, typically remain in the G0 phase and do not undergo further cell division. This allows them to perform their specialized functions without the need for continuous cell division.