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.

What is the expected percent change in the DNA content of a typical eukaryotic cell as it progresses through the cell cycle from the start of the G1 phase to the end of the G2 phase?

Responses

A

-100%

B

-50%

C

+50%

D

+100%

Answer D

Correct. The DNA of a typical eukaryotic cell is replicated in the S phase of the cell cycle, which occurs between the G1 and G2 phases. DNA replication typically results in a increase in the DNA content of a cell.

Researchers tracked the amount of DNA (measured in picograms) over time beginning with a single cell and continuing through several rounds of cell division. The researchers observed threadlike chromosomes prior to cell division. The threadlike chromosomes disappeared from view shortly after each division. The amount of DNA in picograms per cell over several rounds of cell division is shown in Figure 1.

Figure 1. Amount of DNA in picograms per cell over several rounds of cell division

Which of the following statements is consistent with the data in Figure 1?

Responses 

A

The cells have a haploid chromosome number of 3.

B

The cells have a diploid chromosome number of 6.

C

There is a change from 3 to 6 picograms of DNA because DNA is replicated before each round of cell division.

D

There is a change from 6 to 3 picograms of DNA after each cell division because the chromosomes lengthen following cell division.

Answer C

Correct. The change from 3 to 6 picograms of DNA prior to replication indicates that the DNA has been replicated. The replicated DNA is condensed into chromosomes during cell division or mitosis. This ensures that the complete genome from a parent cell is passed on to two genetically identical daughter cells.

DNA replication occurs

Responses

A

during the S phase of the cell cycle

B

as the nuclear envelope breaks down in early mitosis

C

during mitosis but not during meiosis

D

in animal cells but not in plant cells

E

only in cells destined to become gametes

A

during the S phase of the cell cycle

During mitosis, which of the following normally occurs?

Responses

A

Homologous chromosomes pair.

B

Replicated chromosomes line up on the equatorial plate.

C

Tetrads form.

D

Unreplicated chromosomes become oriented in the center of the cell.

E

Maternal and paternal chromatids pair.

B

Replicated chromosomes line up on the equatorial plate.

The drug 5-fluorouracil inhibits thymine production in eukaryotic cells. Which of the following cell cycle stages will be most directly affected by 5-fluorouracil?

Responses

A

The first growth phase (G1)

B

Synthesis of DNA phase (S)

C

Preparation for mitosis (G2)

D

Cytokinesis

Answer B

Correct. DNA synthesis that occurs during S requires thymine−containing nucleotides, so inhibition of thymine production will inhibit DNA synthesis.

Which of the following best describes the role of mitosis in the cell cycle?

Responses

A

Distributing replicated chromosomes to daughter nuclei

B

Dividing the cytoplasm to form four gametes

C

Producing organelles and replicating chromosomes

D

Exchanging genetic material between homologous chromosomes

A

Distributing replicated chromosomes to daughter nuclei

A student used microscopy to investigate the relative lengths of the different stages of mitosis. The student prepared slides of cells isolated from a growing onion root tip and viewed the slides under a dissecting microscope. The student then made diagrams of cells that were in different stages of mitosis and counted the number of cells that were in each of those stages. The student’s data are presented in Table 1.

Table 1. Number of cells in each of four different stages of mitosis

Based on the data, the percent of the mitotic cells that were in metaphase is closest to which of the following?

Responses

A

5%

B

11%

C

18%

D

66%

Answer C

Correct. The number of cells that were in metaphase equals 7, and the total number of mitotic cells equals 38. The percent of mitotic cells in metaphase is calculated as follows: divide 7 by 38 and multiply by 100. The correct answer is 18 percent.

Researchers determined the average amount of time that a particular type of eukaryotic cell spends in each phase of the cell cycle. The data collected by the researchers are represented in Figure 1.

Figure 1. The average amount of time spent by a particular type of eukaryotic cell in each phase of the cell cycle

Based on Figure 1, what percent of the time required to complete a full cycle do the cells typically spend in interphase?

Responses

A

5%

B

35%

C

50%

D

95%

Answer D

Correct. Interphase is composed of the G1, S, G2 and phases. Based on Figure 1, the cells typically spend 19 hours in interphase and require 20 hours total to complete one full cycle. Therefore, 19/20 × 100 = 95%.

Which of the following is true of mitosis?

Responses

A

It is also known as cytokinesis.

B

It maintains the same chromosome number in the daughter cells as in the parent cell.

C

It is the last phase of interphase.

D

It regulates the transfer of genetic information from one daughter cell to another.

E

It moves homologous chromosomes to opposite poles.

B

It maintains the same chromosome number in the daughter cells as in the parent cell.

Researchers studying cell cycle regulation in budding yeast have observed that a mutation in the CDC15 gene causes cell cycle arrest in telophase when the yeast cells are incubated at an elevated temperature. Which of the following statements best predicts the effect of the cell cycle arrest on proliferating yeast cells?

Responses

A

The yeast cells will transition out of G0 but will fail to complete G1 the phase.

B

The yeast cells will initiate mitosis but will fail to complete the G2 phase.

C

The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.

D

The yeast cells will replicate their organelles but will fail to complete the S phase.

Answer C

Correct. Because the cell cycle arrest occurs in telophase, the yeast cells will progress through the cell cycle, including replicating their chromosomes in the S phase, and will enter the M phase but will fail to complete mitosis and cytokinesis.

TABLE 1. DISTRIBUTION OF CONTROL AND EXPERIMENTAL CELLS IN DIFFERENT STAGES OF THE CELL CYCLE AFTER HOURS

	G1	S	G2	M
Control	96	59	48	81
Experimental	142	142	0	0

Researchers claimed that cells treated with radiation are unable to progress through the cell cycle. They tested their claim by exposing a group of cells to radiation (experimental group). A group of unexposed cells served as the control group. After hours, they determined the number of cells in each stage of the cell cycle and confirmed that all differences were statistically significant.

Based on Table 1, which of the following best supports the researchers’ claim?

Responses

A

In the experimental group, no cells were able to enter G2.

B

In the control group, the number of cells in G2 was less than the number of cells in M.

C

In the control group, the number of cells in each stage decreased as the cell cycle continued.

D

In the experimental group, the number of cells in G1 was the same as the number of cells in S.

Answer A

Correct. The lack of cells in the G2 phase supports the researchers’ claim that radiation-treated cells are unable to progress through the cell cycle.

The relative amounts of DNA present in the nucleus of a cell at four different stages of the life cycle are shown in Figure 1.

Figure 1. Relative amounts of DNA present in the nucleus of a cell

Based on Figure 1, which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage?

Responses

A

Stage 1 represents the G2 phase of the cell cycle.

B

Synthesis of sufficient for DNA two daughter cells occurs in stage II.

C

Stage III includes mitosis.

D

The replication of genetic material occurs in stage IV.

Answer B

Correct. Stage II represents the S (synthesis) phase of interphase. The genetic information (DNA) is doubling. If this did not occur, the daughter cells formed as a result of the cell cycle would have too little genetic information (chromosomes). This process is visible on the graph, as the copies of genetic information increase from one to two copies.

A group of researchers cultured yeast cells in a nutrient-rich environment and a nutrient-poor environment and observed the duration of the stages of their cell cycles. The results of their study are summarized in Table 1.

Table 1. Duration (in minutes) of yeast cell cycle phases in a nutrient-rich environment and a nutrient-poor environment

Cell Cycle Stages	Nutrient-rich environment	Nutrient-poor environment
S and G2	23	33
Mitosis	48	61
G1	20	57
Cytokinesis	5	10

The cell cycle of yeast cells grown in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment?

Responses

A

168

B

127

C

179

D

160

Answer A

Correct. Yeast cells in the nutrient-rich environment spend 96 minutes in the cell cycle compared to 161 minutes in the nutrient-poor environment. The percent can be determined by dividing 161 by 96, which results in 1.68 or 168 percent.

A model of the typical life cycle of a cell is shown in Figure 1.

Figure 1. Typical life cycle of a eukaryotic cell

Scientists have estimated that it takes yeast cells approximately 20 hours to complete the entire cycle. Table 1 shows the amount of time in each phase of the life cycle for yeast cells.

Table 1. Amount of time spent in each stage of the cell cycle by yeast cells

Stage	M	G1	S	G2
Time (hours)	2	10	5	3

Based on Table 1, what percent of the life cycle of yeast cells is spent in DNA replication?

Responses

A

5 percent

B

10 percent

C

25 percent

D

50 percent

Answer C

Correct. The yeast cells spend 5 hours out of a total of 20 hours in S phase, which is 25%.