Question 1

Use the data in Table 12.1 to answer the following questions.
The data were obtained from a study of the length of time spent in each phase of the cell cycle by cells of three eukaryotic organisms designated beta, delta, and gamma.
  
Table 12.1: Minutes Spent in Cell Cycle Phases
-Of the following, the best conclusion concerning the difference between the S phases for beta and gamma is that

Accepted Answer

The S phase is part of the cell cycle in which DNA is replicated. If there's a difference in the S phases between beta and gamma, it implies a difference in the amount of DNA being replicated. Therefore, gamma containing more DNA than beta is the most logical conclusion based on the information provided.

Question 2

Use the following information to answer the questions below.
The research team established similar lymphocyte cultures from a number of human donors, including healthy teenagers of both genders, patients already suffering from long-term bacterial infections, and elderly volunteers. They found that the increase in lymphocyte incorporation after pathogen introduction was slightly lower in some of the female teenagers and significantly lower in each of the elderly persons. They repeated the study with a larger number of samples but got the same results.
-Which of the following investigations might be most productive to show what the data on the teenagers might indicate?

Accepted Answer

Testing female teens at different times in their menstrual cycles would allow the researchers to investigate whether the observed decrease in lymphocyte incorporation after pathogen introduction is related to hormonal changes during the menstrual cycle.

Question 3

A particular cell has half as much DNA as some other cells in a mitotically active tissue. The cell in question is most likely in

Accepted Answer

During the S phase of the cell cycle, DNA replication occurs and the amount of DNA in the cell doubles. Therefore, if a cell has half as much DNA as some other cells, it is likely in the G₁ phase, before DNA replication has occurred.

Question 4

The following information applies to the questions below.
Several organisms, primarily protists, have what are called intermediate mitotic organization.
-What is the most probable hypothesis about these intermediate forms of cell division?

Accepted Answer

The presence of intermediate forms of cell division in protists suggests that they have undergone some but not all of the evolutionary steps toward complete mitosis. This is the most probable hypothesis as it is unlikely that these forms of cell division evolved separately from those of other organisms or rely on totally different proteins. It also does not necessarily indicate that these species are not closely related to other protists. It is possible that they are more closely related to plant forms with unusual mitosis, but this is not the most probable hypothesis based on the information provided.

Question 5

Use the following information to answer the questions below.
The research team established similar lymphocyte cultures from a number of human donors, including healthy teenagers of both genders, patients already suffering from long-term bacterial infections, and elderly volunteers. They found that the increase in lymphocyte incorporation after pathogen introduction was slightly lower in some of the female teenagers and significantly lower in each of the elderly persons. They repeated the study with a larger number of samples but got the same results.
-What might be among the research team's conclusions?

Accepted Answer

The research team concluded that the elderly persons had significantly lower lymphocyte incorporation after pathogen introduction, indicating a lowered immune response. This conclusion is supported by the repeated results from the larger sample size. The other options, such as poor nutrition or general health, are not mentioned in the given information and cannot be inferred. Option D is also incorrect as the patient samples are not specified to have had the lowest response. Option E is not mentioned in the given information.

Question 6

Use the following information to answer the questions below.
Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and can therefore be assayed to track their incorporation. In a set of experiments, a student-faculty research team used labeled T nucleotides and introduced these into the culture of dividing human cells at specific times.
-Which of the following questions might be answered by such a method?

Accepted Answer

The incorporation of labeled nucleotides can be used to determine the length of the S phase, as this is when DNA synthesis occurs and the labeled nucleotides would be incorporated into the DNA.

Question 7

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to

Accepted Answer

Vinblastine interferes with the assembly of microtubules, which are crucial components of the mitotic spindle. Therefore, the drug's effectiveness must be related to the disruption of mitotic spindle formation.

Question 8

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the cell cycle would be most disrupted by cytochalasin B?

Accepted Answer

Cytochalasin B inhibits actin function, which is involved in the formation of the contractile ring during cytokinesis. Therefore, cytochalasin B would most disrupt cleavage furrow formation and cytokinesis. The other aspects of the cell cycle listed (spindle formation, spindle attachment to kinetochores, DNA synthesis, and cell elongation during anaphase) are not primarily dependent on actin function.

Question 9

Use the following information to answer the questions below.
Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and can therefore be assayed to track their incorporation. In a set of experiments, a student-faculty research team used labeled T nucleotides and introduced these into the culture of dividing human cells at specific times.
-The research team used the setup to study the incorporation of labeled nucleotides into a culture of lymphocytes and found that the lymphocytes incorporated the labeled nucleotide at a significantly higher level after a pathogen was introduced into the culture. They concluded that

Accepted Answer

The fact that lymphocytes incorporated the labeled nucleotide at a significantly higher level after a pathogen was introduced into the culture indicates that infection causes lymphocytes to divide more rapidly. Therefore, option C is the correct choice, while options A, B, D, and E are not supported by the given information.

Question 10

The following information applies to the questions below.
Several organisms, primarily protists, have what are called intermediate mitotic organization.
-These protists are intermediate in what sense?

Accepted Answer

The intermediate mitotic organization in these protists refers to their maintenance of a nuclear envelope during division. This is in contrast to typical mitosis seen in most eukaryotes, where the nuclear envelope breaks down during division.

Question 11

Use the data in Table 12.1 to answer the following questions.
The data were obtained from a study of the length of time spent in each phase of the cell cycle by cells of three eukaryotic organisms designated beta, delta, and gamma.
  
Table 12.1: Minutes Spent in Cell Cycle Phases
-The best conclusion concerning delta is that the cells

Accepted Answer

The data in Table 12.1 shows that Delta cells spend the most time in the G₀ phase (720 minutes) and the least time in the S and G₂ phases. This suggests that Delta cells are actually in the G₀ phase, which is a non-dividing phase of the cell cycle that occurs when cells exit the cycle and enter a resting phase. Therefore, choice D is the best conclusion.

Question 12

Use the following information to answer the questions below.
A student is looking through his light microscope (~450 X) at a squashed and stained onion root tip. Some, but not all, of the cells have clearly visible chromosome strands.
-When the cell has just completed telophase, which of the following does he see?

Accepted Answer

When a cell has just completed telophase, the chromosomes de-condense back into chromatin, and the nuclear envelope re-forms around each set of chromosomes, resulting in two daughter nuclei. The cell itself is divided into two through cytokinesis, leading to two smaller cells with chromatin.

Question 13

Use the following information to answer the questions below.
Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and can therefore be assayed to track their incorporation. In a set of experiments, a student-faculty research team used labeled T nucleotides and introduced these into the culture of dividing human cells at specific times.
-Once they had determined which cells were dividing, the team wanted to use a non-radioactive method to track whether various physiological factors (such as food or body temperature)affect the action of the pathogen. Which of the following would be effective, simple, and safe?

Accepted Answer

Counting the frequency of cells in mitosis would be the most effective and simple method to track the effect of physiological factors on DNA incorporation without using radioactive labeling. This method utilizes microscopy to identify dividing cells, and it is safe since it only involves observing the cells and does not require any chemical or biological manipulations. Measuring picograms of DNA or counting newly formed plasma membranes would not provide direct information on DNA incorporation and are more complicated methods. Measuring the number of chromosomes or chromatids may not accurately reflect DNA incorporation since abnormalities in chromosome structure or number can occur during cell division.

Question 14

Which of the following does not occur during mitosis?

Accepted Answer

DNA replication occurs during the S phase of interphase, which precedes mitosis. During mitosis, the replicated chromosomes condense, the spindle fibers form, and sister chromatids separate, but no further replication of DNA occurs.

Question 15

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in

Accepted Answer

Mitosis without cytokinesis will result in cells with multiple nuclei because the chromosomes will duplicate but the cytoplasm will not divide.

Question 16

Use the following information to answer the questions below.
A student is looking through his light microscope (~450 X) at a squashed and stained onion root tip. Some, but not all, of the cells have clearly visible chromosome strands.
-When a cell is in anaphase of mitosis, which of the following will he see?

Accepted Answer

The answer of Use the following information to answer the...

Question 17

One difference between cancer cells and normal cells is that cancer cells

Accepted Answer

One difference between cancer cells and normal cells is that cancer cells continue to divide even when they are tightly packed together, whereas normal cells undergo density-dependent inhibition, which prevents further cell division when cells become tightly packed.

Therefore, the correct choice is C.

Question 18

Through a microscope, you can see a cell plate beginning to develop across the middle of a cell and nuclei forming on either side of the cell plate. This cell is most likely

Accepted Answer

The development of a cell plate across the middle of a cell, and the formation of nuclei on either side of the cell plate, are characteristic of cytokinesis in plant cells, which is the process by which a single cell divides into two daughter cells. Animal cells, on the other hand, form a cleavage furrow rather than a cell plate during cytokinesis, and bacterial cells divide by binary fission, which does not involve the formation of a cell plate or nuclei. The S phase of the cell cycle is characterized by DNA synthesis, which would not be visible under a microscope in the way described in the question. Finally, metaphase is a stage of mitosis, not cytokinesis, and would not involve the formation of a cell plate.

Question 19

The decline of MPF activity at the end of mitosis is due to

Accepted Answer

MPF activity is due to the presence of cyclin and Cdk (cyclin-dependent kinase). At the end of mitosis, cyclin is degraded, leading to the decline of MPF activity.

Quiz 12: The Cell Cycle