AP Biology 4.5 - Cell Cycle (Mitosis Only

The relative amount of in a cell at various stages of the cell cycle is shown in Figure 1 .

Figure 1. Amount of per cell during different stages of the cell cycle, relative to the beginning of the stage

Which of the following best describes how the amount of in the cell changes during  phase?

Responses

A

The amount of DNA doubles as the DNA is replicated.

B

The amount of DNA slightly increases as a result of new organelle synthesis.

C

The amount of DNA does not change while the cell grows.

D

The amount of DNA is halved as the cell divides into two daughter cells.

Answer D

Correct. During mitosis, sister chromatids are separated, two nuclei form, and cytokinesis results in the formation of two new cells. Each daughter cell has the same number of chromosomes as the original parent cell.

A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best explains what the next process will be in the cell?

Responses

A

Homologous chromosomes (each with two sister chromatids) will move toward opposite poles of the cell.

B

Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.

C

The nuclear envelope will break down, and the spindle will begin to form.

D

The chromatin will decondense, and the daughter cell will enter interphase.

B

Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.

Which of the following best describes a cell that is in the G1 stage of the cell cycle?

Responses

A

The cell is growing in size and increasing its number of proteins and organelles.

B

The chromosomes within the cell are checked to make certain that they have been replicated correctly.

C

The chromosomes are replicating, and the amount of DNA in the cell is doubling.

D

The cell is in a resting stage and no longer dividing.

Answer A

Correct. The cellular activities described are activities that occur during the stage of the G1 cell cycle.

A cell culture commonly used in research was selected to study the effect of a specific virus on the timing of cell cycle phases. Two separate cultures were started, one untreated and one inoculated with the virus. Both cultures were incubated under identical conditions. After a period of time, 200 cells from each culture were observed and classified as shown in Table 1.

Table 1. Number of normal and infected cells found in three phases of the cell cycle

Phase of Cell Cycle	Untreated Cells (n=200)	Virus-Infected Cells (n=200)
	196	10
Interphase	2	40
Mitosis	2	150

Which of the following most accurately describes an observation and an effect of the viral infection indicated by the data in Table 1?

Responses

A

Normal cells spend 98 percent of their time cycling in and out of interphase. The virus reduces this to 5 percent of the time.

B

Twenty percent of the virus-infected cells are in interphase. These cells are no longer part of the cell cycle.

C

Forty percent of the virus-infected cells are in interphase. These cells are preparing for replication of genetic material.

D

Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.

Answer D

Correct. One hundred fifty out of 200 is 75 percent. The virus activates cells currently in G0 the phase, leading to rapid cell growth and division.

Researchers performed an experiment to determine the effect of certain genetic mutations on mitosis in tropical fruit fly embryos. They determined the percentage of cells in each of four phases of mitosis as shown in Figure 1.

Figure 1. Percent of cells in phases of mitosis

Which of the following patterns is shown by the data?

Responses

A

Mutant 1 cells are more similar to mutant 3 cells than to wild-type cells.

B

In wild-type cells, the percent of cells in anaphase is twice the amount of those in telophase

C

In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.

D

The percent of mutant 2 cells in anaphase is higher than that of mutant 1 cells.

Answer C

Correct. According the data, mutant 3 had the highest percent of cells in prophase/prometaphase of all cell types and the least time in anaphase and telophase.

If chemical signals in the cytoplasm control the progression of a cell to the M phase of the cell cycle, then fusion of a cell in G₁ with a cell in early M phase would most likely result in the

Responses

A

replication of chromosomes only in the G₁ cell

B

exiting of both cells from the cell cycle and into the G₀ phase

C

condensation of chromatin in preparation of nuclear division in both cells

D

transfer of organelles from the G₁ cell to the cell in the M phase

C

condensation of chromatin in preparation of nuclear division in both cells

Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division.

 

Figure 1. Number of chromosomes in a human cell at different stages of cell division

Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ?

Responses

A

DNA replication occurs between metaphase and anaphase, doubling the number of chromosomes. Between telophase and cytokinesis, the cell divides in two, with each cell receiving half of the replicated chromosomes.

B

New chromosomes formed during prophase are doubled during anaphase and are recombined before cytokinesis.

C

Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase, the chromatids are separated, each becoming a chromosome. Cytokinesis distributes the chromosomes into two separate cells.

D

At anaphase a cell contains two identical copies of each chromosome, but following telophase, one of the copies is broken down into nucleotides.

Answer C

Correct. This statement accurately describes changes in the chromosome number during the different stages of cell division as represented in the graph. During prophase and metaphase, each chromosome is composed of two chromatids. During anaphase, the two chromatids separate to the opposite ends of the cell, doubling the number of chromosomes in the cell. The number of DNA  strands in the cell has not changed, only how they are organized. During cytokinesis, the cell is divided into two daughter cells, each containing half of the chromosomes found in the parent cell during anaphase and telophase.

Researchers grew seedlings of corn, Zea mays, in loose and compact sand. The researchers measured the amount of time required for the cells in the growing root tips of the seedlings to double in number. The mean cell doubling times for the two groups of seedlings are shown in Figure 1.

Figure 1. Mean cell doubling times for the growing root tips of Zea mays seedlings planted in loose or compact sand

Based on the sample means, which of the following conclusions about the cells in the growing root tips of Zea mays seedlings is best supported by the results of the experiment?

Responses

A

The cells of the root tips grow to larger sizes when the seedlings are planted in compact sand than when the seedlings are planted in loose sand.

B

The average rate of mitotic cell division is greater for the root tips growing in loose sand than for the root tips growing in compact sand.

C

The average cell cycle time is greater for the root tips growing in compact sand than for the root tips growing in loose sand.

D

More cells are produced per unit of time in the root tips growing in compact sand than in the root tips growing in loose sand.

Answer D

Correct. According to the figure, the mean cell doubling time of Zea mays seedling root tips in compact sand is less than in loose sand. A lower mean cell doubling time indicates an increased rate of mitotic cell division for cells of root tips in compact sand.