5) Scientists isolate cells in various phases of the cell cycle. They find a group of cells that have 1.5 times more DNA than G1 phase cells. The cells of this group are _____.

A) between the G1 and S phases in the cell cycle

B) in the G2 phase of the cell cycle
C) in the M phase of the cell cycle
D) in the S phase of the cell cycle

Answer: D

6) The first gap in the cell cycle (G1) corresponds to _____.

A) normal growth and cell function
B) the phase in which DNA is being replicated
C) the beginning of mitosis
D) the phase between DNA replication and the M phase

Answer: A

7) The microtubule-organizing center found in animal cells is an identifiable structure present during all phases of the cell cycle. Specifically, it is known as the _____.
A) microtubulere
B) centrosome

C) centromere
D) kinetochore

Answer: B

8) In human and many other eukaryotic species' cells, the nuclear membrane has to disappear to permit _____.
A) cytokinesis
B) the attachment of microtubules to kinetochores

C) the splitting of the centrosomes
D) the disassembly of the nucleolus

Answer: B

9) The mitotic spindle is a microtubular structure that is involved in _____.

A) splitting of the cell (cytokinesis) following mitosis
B) triggering the compaction and condensation of chromosomes
C) dissolving the nuclear membrane

D) separation of sister chromatids

Answer: D

10) Metaphase is characterized by _____.
A) aligning of chromosomes on the equator
B) splitting of the centromeres
C) cytokinesis
D) separation of sister chromatids

Answer: A

11) Kinetochore microtubules assist in the process of splitting centromeres by _____.

A) using motor proteins to split the centromere at specific arginine residues
B) creating tension by pulling toward opposite poles
C) sliding past each other like actin filaments

D) phosphorylating the centromere, thereby changing its conformation

Answer: B

12) Some cells have several nuclei per cell. How could such multinucleated cells be explained?

A) The cell underwent repeated cytokinesis but no mitosis.
B) The cell underwent repeated mitosis with simultaneous cytokinesis.
C) The cell underwent repeated mitosis, but cytokinesis did not occur.

D) The cell had multiple S phases before it entered mitosis.

Answer: C

13) How is plant cell cytokinesis different from animal cell cytokinesis?
A) The contractile filaments found in plant cells are structures composed of carbohydrates; the cleavage furrow in animal cells is composed of contractile phospholipids.
B) Plant cells deposit vesicles containing cell-wall building blocks on the metaphase plate; animal cells form a cleavage furrow.
C) The structural proteins of plant cells separate the two cells; in animal cells, a cell membrane separates the two daughter cells.
D) Plant cells divide after metaphase but before anaphase; animal cells divide after anaphase.

Answer: B

14) FtsZ is a bacterial cytoskeletal protein that forms a contractile ring involved in bacterial cytokinesis. Its function is analogous to _____.
A) the cleavage furrow of eukaryotic animal cells
B) the cell plate of eukaryotic plant cells

C) the mitotic spindle of eukaryotic cells
D) the microtubule-organizing center of eukaryotic cells

Answer: A

15) At which phase are centrioles beginning to move apart in animal cells?

A) anaphase
B) prometaphase
C) metaphase

D) prophase

Answer: D

16) If there are 20 centromeres in a cell at anaphase, how many chromosomes are there in each daughter cell following cytokinesis?
A) 10
B) 20

C) 40
D) 80

Answer: A

17) Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol disrupts microtubule formation. Surprisingly, this stops mitosis. Specifically, Taxol must affect _____.
A) the structure of the mitotic spindle
B) anaphase
C) formation of the centrioles
D) chromatid assembly

Answer: A

18) Which of the following are primarily responsible for cytokinesis in plant cells but not in animal cells?
A) kinetochores
B) Golgi-derived vesicles

C) actin and myosin
D) centrioles and centromeres

Answer: B

19) Movement of the chromosomes during anaphase would be most affected by a drug that prevents _____.
A) nuclear envelope breakdown
B) elongation of microtubules

C) shortening of microtubules
D) formation of a cleavage furrow

Answer: C

20) Measurements of the amount of DNA per nucleus were taken on a large number of cells from a growing fungus. The measured DNA levels ranged from 3 to 6 picograms per nucleus. In which stage of the cell cycle did the nucleus contain 6 picograms of DNA?
A) G1
B) S
C) G2

D) M

Answer: C

21) A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. How many picograms would be found at the end of S and the end of G2?

A) 8; 8
B) 8; 16
C) 16; 8
D) 16; 16

Answer: D

22) The beginning of anaphase is indicated by which of the following?

A) Chromatids lose their kinetochores.
B) Cohesin attaches the sister chromatids to each other.
C) Cohesin is cleaved enzymatically.

D) Spindle microtubules begin to polymerize.

Answer: C

23) During which phase of mitosis do the chromatids become chromosomes?

A) telophase
B) anaphase
C) prophase

D) metaphase

Answer: B

24) A cleavage furrow is _____.
A) a ring of vesicles forming a cell plate
B) the separation of divided prokaryotes
C) a groove in the plasma membrane between daughter nuclei
D) the space that is created between two chromatids during anaphase

Answer: C

27) If the cell whose nuclear material is shown in the accompanying figure continues toward completion of mitosis, which of the following events would occur next?
A) spindle fiber formation
B) nuclear envelope breakdown

C) formation of telophase nuclei
D) synthesis of chromatids

Answer: C

Several organisms, primarily protists, have what are called intermediate mitotic organization.

32) These protists are intermediate in what sense?
A) They reproduce by binary fission in their early stages of development and by mitosis when they are mature.
B) They use mitotic division but only have circular chromosomes.
C) They maintain a nuclear envelope during division.
D) None of them form spindles.

Answer: C

Several organisms, primarily protists, have what are called intermediate mitotic organization.

33) What is the most probable hypothesis about these intermediate forms of cell division?
A) They represent a form of cell reproduction, which must have evolved completely separately from those of other organisms.
B) They rely on totally different proteins for the processes they undergo.
C) They may be more closely related to plant forms that also have unusual mitosis.
D) They show some but not all of the evolutionary steps toward complete mitosis.

Answer: D

Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and, therefore, can 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.

34) Which of the following questions might be answered by using the method described? A) How many cells are produced by the culture per hour?
B) What is the length of the S phase of the cell cycle?
C) How many picograms of DNA are made per cell cycle?

D) When do spindle fibers attach to chromosomes?

Answer: B

Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and, therefore, can 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.

35) The research team used their experiments 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 _____.
A) the presence of the pathogen made the experiments too contaminated to trust the results
B) infection causes lymphocytes to divide more rapidly
C) infection causes cell cultures in general to reproduce more rapidly
D) infection causes lymphocyte cultures to skip some parts of the cell cycle

Answer: B

36) 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 _____.
A) an animal cell in the process of cytokinesis
B) a plant cell in the process of cytokinesis

C) an animal cell in the S phase of the cell cycle

D) a plant cell in metaphase

Answer: B

37) Which of the following does NOT occur during mitosis?

A) condensation of the chromosomes
B) replication of the DNA
C) spindle formation

D) separation of the spindle poles

Answer: B

38) 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?
A) spindle formation
B) spindle attachment to kinetochores

C) cell elongation during anaphase
D) cleavage furrow formation and cytokinesis

Answer: D

39) Motor proteins require which of the following to function in the movement of chromosomes toward the poles of the mitotic spindle?
A) intact centromeres
B) a microtubule-organizing center

C) ATP as an energy source
D) synthesis of cohesin

Answer: C

41) Neurons and some other specialized cells divide infrequently because they _____.

A) no longer have active nuclei
B) have entered into G0

C) can no longer bind Cdk to cyclin
D) show a drop in MPF concentration

Answer: B

42) MPF is a dimer consisting of _____.

A) a growth factor and mitotic factor
B) ATP synthetase and a protease
C) cyclin and tubulin

D) cyclin and a cyclin-dependent kinase

Answer: D

43) Cyclin-dependent kinase (Cdk) is _____.
A) inactive, or "turned off," in the presence of cyclin
B) present only during the S phase of the cell cycle
C) the enzyme that catalyzes the attachment of chromosomes to microtubules

D) an enzyme that attaches phosphate groups to other proteins

Answer: D

44) What happens if MPF (mitosis-promoting factor) is introduced into immature frog oocytes that are arrested in G2?

A) Nothing happens.
B) The cells undergo meiosis.
C) The cells enter mitosis.
D) Cell differentiation is triggered.

Answer: C

45) Once a cell completes mitosis, molecular division triggers must be turned off. What happens to MPF during mitosis?
A) It is completely degraded.
B) It is exported from the cell.

C) The cyclin component of MPF is degraded.
D) The Cdk component of MPF is degraded and exported from the cell.

Answer: C

46) The M-phase checkpoint ensures that all chromosomes are attached to the mitotic spindle. If this does not happen, cells would most likely be arrested in _____.
A) telophase
B) prophase

C) prometaphase
D) metaphase

Answer: D

47) Which of the following is released by platelets in the vicinity of an injury?

A) PDGF
B) MPF
C) cyclin

D) Cdk

Answer: A

48) Which of the following is a protein synthesized at specific times during the cell cycle that associates with a kinase to form a catalytically active complex?
A) PDGF
B) MPF

C) cyclin
D) Cdk

Answer: C

49) Which of the following is a protein maintained at steady levels throughout the cell cycle that requires cyclin to become catalytically active?
A) PDGF
B) MPF

C) cyclin
D) Cdk

Answer: D

50) Which of the following triggers the cell's passage past the G2 checkpoint into mitosis? A) PDGF

B) MPF
C) cyclin
D) Cdk

Answer: B

51) The cyclin component of MPF is destroyed toward the end of which phase?

A) G1

B) S

C) G2

D) M

Answer: D

53) Density-dependent inhibition is explained by which of the following?
A) As cells become more numerous, they begin to squeeze against each other, restricting their size and ability to produce control factors.
B) As cells become more numerous, the cell surface proteins of one cell contact the adjoining cells and they stop dividing.
C) As cells become more numerous, the protein kinases they produce begin to compete with each other, such that the proteins produced by one cell essentially cancel those produced by its neighbor.
D) As cells become more numerous, the level of waste products increases, eventually slowing down metabolism.

Answer: B

54) Besides the ability of some cancer cells to overproliferate, what else could logically result in a tumor?
A) changes in the order of cell cycle stages
B) lack of appropriate cell death

C) inability to form spindles
D) inability of chromosomes to meet at the metaphase plate

Answer: B

55) Anchorage dependence of animal cells in vitro or in vivo depends on which of the following?

A) attachment of spindle fibers to centrioles
B) response of the cell cycle controls to signals from the plasma membrane
C) the binding of cell-surface phospholipids to those of adjoining cells

D) response of the cell cycle controls to the binding of cell-surface phospholipids

Answer: B

56) A research team began a study of a cultured cell line. Their preliminary observations showed them that the cell line did not exhibit either density-dependent inhibition or anchorage dependence. What could they conclude right away?
A) The cells are unable to form spindle microtubules.

B) They have altered the series of cell cycle phases.
C) The cells show characteristics of tumors.
D) They were originally derived from an elderly organism.

Answer: C

57) For a chemotherapeutic drug to be useful for treating cancer cells, which of the following is most desirable?
A) It is safe enough to limit all apoptosis.
B) It does not alter metabolically active cells.

C) It interferes with cells entering G0.
D) It interferes with rapidly dividing cells.

Answer: D

58) Cells from advanced malignant tumors often have very abnormal chromosomes and an abnormal number of chromosomes. What might explain the association between malignant tumors and chromosomal abnormalities?
A) Cancer cells are no longer density-dependent.

B) Cancer cells are no longer anchorage-dependent.
C) Cell cycle checkpoints are not in place to stop cells with chromosome abnormalities.

D) Transformation introduces new chromosomes into cells.

Answer: C

59) Exposure of zebrafish nuclei to meiotic cytosol resulted in phosphorylation of NEP55 and L68 proteins by cyclin-dependent kinase 2. NEP55 is a protein of the inner nuclear membrane, and L68 is a protein of the nuclear lamina. What is the most likely role of phosphorylation of these proteins in the process of mitosis?

A) They enable the attachment of the spindle microtubules to kinetochore regions of the centromere.
B) They are involved in the disassembly and dispersal of the nucleolus.
C) They are involved in the disassembly of the nuclear envelope.

D) They assist in the movement of the centrosomes to opposite sides of the nucleus

Answer: C

60) Density-dependent inhibition is a phenomenon in which crowded cells stop dividing at some optimal density and location. This phenomenon involves binding of a cell-surface protein to its counterpart on an adjoining cell's surface. A growth inhibiting signal is sent to both cells, preventing them from dividing. Certain external physical factors can affect this inhibition mechanism.

Select the statement that makes a correct prediction about natural phenomena that could occur during the cell cycle to prevent cell growth.
A) As cells become more numerous, they begin to squeeze against each other, restricting their size and ability to allow cell growth.

B) As cells become more numerous, the protein kinases they produce begin to compete with each other until only one cell has the proteins necessary for growth.
C) As cells become more numerous, the amount of required growth factors and nutrients per cell becomes insufficient to allow for cell growth.

D) As cells become more numerous, more and more of them enter the synthesis part of the cell cycle and duplicate DNA to inhibit cell growth.

Answer: C