Raven/Johnson Biology 8e - DOC by 9h9O9MR

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									Raven/Johnson Biology 8e                                              Chapter 19 Answers
   1. Which of the following developmental stages is associated with the generation of organs?
        a. Growth
        b. Pattern formation
        c. Differentiation
        d. Morphogenesis

The correct answer is d—
   A. Answer a is incorrect. The growth phase in development is associated with rapid cell
       division.

The correct answer is d—
   B. Answer b is incorrect. Pattern formation is associated with the establishment of the body
       plan.

The correct answer is d—
   C. Answer c is incorrect. Differentiation is associated with changes in gene expression that
       determines cell fate.

The correct answer is d—Morphogenesis
   D. Answer d is correct. Morphogenesis leads to the development of organs.

   2. Growth of the developing embryo involves rapid _________ cell divisions.
         a. mitotic
         b. meiotic
         c. binary fission
         d. sexual

The correct answer is a—mitotic
   A. Answer a is correct. Cleavage of the developing embryo occurs through mitotic cell
       division.

The correct answer is a—
   B. Answer b is incorrect. Meiosis produces haploid cells. The cells of the developing embryo
       are all diploid.

The correct answer is a—
   C. Answer c is incorrect. Binary fission cell division is associated with prokaryotic cells.

The correct answer is a—
   D. Answer d is incorrect. Sexual cell division is another name for meiosis. The cells
       produced through meiosis are haploid, but developing embryos are diploid.

   3. The reduced size of a blastomere is the consequence of a shortened—
         a. M phase
         b. S phase
         c. G1 and G2 phases
         d. all of the above

The correct answer is c—
Raven/Johnson Biology 8e                                                Chapter 19 Answers
   A. Answer a is incorrect. M (mitotic) phase is not altered during development. It takes a
      finite amount of time to separate the DNA during mitosis.

The correct answer is c—
   B. Answer b is incorrect. S phase is not altered during development. It takes a finite amount
       of time to replicate DNA.

The correct answer is c—G1 and G2
   C. Answer c is correct. The growth phases G1 and G2 do not require a set amount of time. By
       spending less time in G phases, the cell produces less cytoplasmic contents and therefore
       is smaller.

The correct answer is c—
   D. Answer d is incorrect. The M phase and S phase of the cell cycle are the same.

   4. A pluripotent cell is one that can—
         a. become any cell type
         b. produce an indefinite supply of a single cell type
         c. produce a limited amount of a specific cell type
         d. produce multiple cell types

The correct answer is d—
   A. Answer a is incorrect. A totipotent cell can become any cell type—pluripotent cells have a
       more limited potential.

The correct answer is d—
   B. Answer b is incorrect. Pluripotent cells can make an indefinite number of cells; however,
       they are capable of differentiation into many different cell types.

The correct answer is d—
   C. Answer c is incorrect. Pluripotent cells can make an indefinite number of cells, and they
       are capable of differentiation into many different cell types.

The correct answer is d—produce multiple cell types
   D. Answer d is correct. Pluripotent cells retain the potential to differentiate into a defined set
       of cells.

   5. Which of the following statements is NOT true regarding embryonic stem (ES) cells?
        a. They retain the ability to develop into any cell type.
        b. They are isolated from the inner cell mass of a developing embryo.
        c. They are tissue-specific.
        d. They are totipotent.

The correct answer is c—
   A. Answer a is incorrect. The power of stem cells is their ability to differentiate into any
       number of useful cell types.

The correct answer is c—
Raven/Johnson Biology 8e                                               Chapter 19 Answers
   B. Answer b is incorrect. ES cells are isolated from the inner cell mass of a developing
      chorate.

The correct answer is c—They are tissue-specific.
   C. Answer c is correct. ES cells are not tissue-specific. As an embryonic stem cell, ES allows
       for the production of many different cell types.

The correct answer is c—
   D. Answer d is incorrect. ES cells are totipotent.

   6. Plant meristems—
         a. are only present during development
         b. contain stem cells
         c. undergo meiosis
         d. all of the above

The correct answer is b—
   A. Answer a is incorrect. Plant meristems are present throughout the life of the plant.

The correct answer is b—contain stem cells
   B. Answer b is correct. A meristem is a collection of plant stem cells.

The correct answer is b—
   C. Answer c is incorrect. Rapid cell division requires mitosis, not meiosis.

The correct answer is b—
   D. Answer d is incorrect. Only one of the answers is correct. Meristems are present
       throughout the life of a cell, and they support growth through mitotic cell division.

   7. What is the common theme in cell determination by induction or cytoplasmic
      determinants?
          a. The activation of transcription factors
          b. The activation of cell signaling pathways
          c. A change in gene expression
          d. Both a and c

The correct answer is d—
   A. Answer a is incorrect. Activation of transcription factors is a common theme; however,
       this activation results in a change in gene expression.

The correct answer is d—
   B. Answer b is incorrect. Activation of signaling pathways is a characteristic of induction,
       but not cytoplasmic determinants.

The correct answer is d—
   C. Answer c is incorrect. A change in gene expression is a common theme; however, this
       change is the result of activation of transcription factors.

The correct answer is d—Both a and c
Raven/Johnson Biology 8e                                               Chapter 19 Answers
   D. Answer d is correct. Both induction and cytoplasmic determinates influence development
      by activating transcription factors leading to a change in gene expression.

   8. Which of the following is NOT a limitation to reproductive cloning?
        a. Efficiency of the process
        b. Ethical considerations
        c. Sources for donor DNA
        d. Genetic imprinting of the DNA

The correct answer is c—
   A. Answer a is incorrect. Reproductive cloning has a very low success rate and even when it
       works, the clones are much more susceptible to diseases.

The correct answer is c—
   B. Answer b is incorrect. Major ethical considerations are associated with the use of this
       technique—especially for the reproduction of humans.

The correct answer is c—Sources for donor DNA
   C. Answer c is correct. Reproductive cloning has been successfully conducted for a wide
       range of animals.

The correct answer is c—
   D. Answer d is incorrect. Genetic imprinting is a major problem limiting the success of this
       technique.

   9. How do the products of therapeutic cloning differ from those of reproductive cloning?
        a. Therapeutic cloning provides a source of embryonic stem cells.
        b. Therapeutic cloning produces an embryo that can be implanted into a uterus.
        c. Therapeutic cloning produces whole tissues or organs.
        d. Therapeutic cloning provides a source of proteins.

The correct answer is a—Therapeutic cloning provides a source of embryonic stem cells.
   A. Answer a is correct. Therapeutic cloning generates ES cells from a cloned cell by
       disrupting the cloned embryo early in development.

The correct answer is a—
   B. Answer b is incorrect. Therapeutic cloning does not allow development of the clone
       progress past the blastocyst stage.

The correct answer is a—
   C. Answer c is incorrect. Therapeutic cloning can provide a source of cells that could be
       differentiated into a specific cell type; however, these cells will not automatically form
       whole tissues or organs.

The correct answer is a—
   D. Answer d is incorrect. Therapeutic cloning generates ES cells. The expression of specific
       proteins is accomplished through other molecular biological techniques (for example,
       transgenes).
Raven/Johnson Biology 8e                                              Chapter 19 Answers
   10. The anterior–posterior axis of the fruit fly Drosophila is determined by—
          a. growth factors
          b. zygotic RNA
          c. morphogens
          d. cellular blastoderm formation

The correct answer is c—
   A. Answer a is incorrect. Growth factors are important in determining cell differentiation.
       Orientation of the body plan is regulated by morphogens.

The correct answer is c—
   B. Answer b is incorrect. Zygotic RNA is not produced or expressed until later in
       development.

The correct answer is c—morphogens
   C. Answer c is correct. Morphogens like Bicoid and Nanos regulate the expression of other
       proteins leading to the establishment of polarity in the developing embryo.

The correct answer is c—
   D. Answer d is incorrect. Cellular blastoderm formation is an important stage in the
       development of the fly; however it does not directly influence the A–P axis determination.

   11. Which of the following best describes a morphogen?
         a. A cell that secretes a diffusible signal that specifies cell fate
         b. A diffusible signal that functions to determine cell fate
         c. A protein that helps mediate cell–cell interactions, altering cell fate
         d. A protein that allows a cell to become totipotent

The correct answer is b—
   A. Answer a is incorrect. A morphogen is a protein, not a cell.

The correct answer is b—A diffusible signal that functions to determine cell fate
   B. Answer b is correct. Morphogens function to alter gene expression and therefore alter cell
       fate.

The correct answer is b—
   C. Answer c is incorrect. Morphogens are not cell adhesion molecules.

The correct answer is b—
   D. Answer d is incorrect. Morphogens move the cell away from totipotency by contributing
       to differentiation.

   12. Suppose that during a mutagenesis screen to isolate mutations in Drosophila, you come
       across a fly with legs growing out of its head. What gene cluster is likely affected?
           a. Bicoid
           b. Hunchback
           c. Bithorax
           d. Antennapedia
Raven/Johnson Biology 8e                                                Chapter 19 Answers
The correct answer is d—
   A. Answer a is incorrect. Bicoid is a gene for a morphogen involved in establishing the
       anterior–posterior axis of the fly.

The correct answer is d—
   B. Answer b is incorrect. Hunchback is a gene that is associated with the development of
       anterior structures in the fly.

The correct answer is d—
   C. Answer c is incorrect. Bithorax is a cluster of homeotic genes that control the
       development of body parts in the thorax and abdomen.

The correct answer is d—Antennapedia
   D. Answer d is correct. Antennapedia is a cluster of homeotic genes that control the
       development of body parts at the anterior end of the fly.

   13. What would be the likely result of a mutation of the bcl-2 gene on the level of apoptosis?
         a. No change
         b. A decrease in apoptosis
         c. An increase in apoptosis
         d. An initial increase, followed by a decrease in apoptosis

The correct answer is c—
   A. Answer a is incorrect. The role of bcl-2 is to inhibit activation of the proteases that cause
       apoptosis. If bcl-2 is not functioning then there will be no regulation of protease activity.

The correct answer is c—
   B. Answer b is incorrect. Since bcl-2 functions to inhibit apoptosis, the loss of regulation
       would lead to more, not less, apoptosis.

The correct answer is c—An increase in apoptosis
   C. Answer c is correct. The activity of the proteases responsible for cell death is regulated by
       bcl-2. In the absence of this regulation there would be more apoptosis.

The correct answer is c—
   D. Answer d is incorrect. The role of bcl-2 is to inhibit activation of the proteases that cause
       apoptosis. If bcl-2 is not functioning then there will be no regulation of protease activity.

   14. How is the body plan of a plant first determined?
         a. The activity of MADS box genes
         b. The first cell division following fertilization
         c. Gastrulation
         d. Both a and b

The correct answer is b—
   A. Answer a is incorrect. The MADS box genes regulate pattern formation of specific body
       regions (such as leaf, petal, root) of the plant.

The correct answer is b—The first cell division following fertilization
Raven/Johnson Biology 8e                                               Chapter 19 Answers
   B. Answer b is correct. The first cell division in plants is unequal; producing one large
      daughter cell that will become the suspensor and a second, smaller daughter cell that goes
      on to develop into the plant embryo.

The correct answer is b—
   C. Answer c is incorrect. The cell wall surrounding plant cells prohibits their movement.
       Gastrulation requires that cells move.

The correct answer is b—
   D. Answer d is incorrect. The unequal cell division following fertilization determines the
       body plan of the plant; however, the MADS box genes are not involved in this process.

   15. How does an endocrine-disrupting chemical (EDC) affect development?
         a. It alters the normal pathway of endocrine hormone activity
         b. It induces mutations
         c. It alters the sex determination of the developing embryo
         d. Both a and b

The correct answer is d—
   A. Answer a is incorrect. Endocrine-disrupting chemicals influence the normal role of
       endocrine hormones on development by altering their production, transport, or receptor
       binding; however, there is evidence that exposure the EDCs can result in heritable
       changes in the genome.

The correct answer is d—
   B. Answer b is incorrect. Exposure to EDCs can affect the phenotype of an individual but
       this is an acquired trait that is not passed on. EDCs are not usually mutagens.

The correct answer is d—
   C. Answer c is incorrect. Although endocrines are associated with sex determination, the
       EDCs appear to influence development of the sex organs.

The correct answer is d—Both a and b
   D. Answer d is correct. Environmental toxins that are classified as EDCs can have a
       profound and long-lasting influence on development.

Challenge Questions

       1. The fate map for C. elegans (refer to Figure 19.3) diagrams development of a
          multicellular organism from a single cell. Use this fate map to determine the number
          of cell divisions required to establish the population of cells that will become (a) the
          nervous system and (b) the gonads.

Answer—The horizontal lines of the fate map represent cell divisions. Starting with the egg, four
cell divisions are required to establish a population of cells that will become nervous tissue. It
takes another eight to nine divisions to produce the final number of cells that will make up the
nervous system of the worm. It takes seven to eight rounds of cell division to generate the
population of cells that will become the gonads. Once established, another seven to eight cell
divisions are required to produce the actual gonad cells.
Raven/Johnson Biology 8e                                               Chapter 19 Answers



       2. Carefully examine the C. elegans fate map in Figure 19.3. Notice that some of the
          branchpoints (daughter cells) do not go on to produce more cells. What is the cellular
          mechanism underlying this pattern?

Answer—Not every cell in a developing embryo will survive. The process of apoptosis is
responsible for eliminating cells from the embryo. In C. elegans, the process of apoptosis is
regulated by three genes: ced-3, ced-4, and ced-9. Both ced-3 and ced-4 encode proteases,
enzymes that degrade proteins. Interestingly, the ced-3 protease functions to activate gene
expression of the ced-4 protease. Together, these proteases will destroy the cell from the inside-
out. The ced-9 gene functions to repress the activity of the protease-encoding genes, thereby
preventing apoptosis.

       3. You have generated a set of mutant embryonic mouse cells. Predict the developmental
          consequences for each of the following mutations.
             a. Knockout mutation for N-cadherin
             b. Knockout mutation for integrin
             c. Deletion of the cytoplasmic domain of integrin

Answer—These cell adhesion proteins (N-cadherin and integrin) play an important role in
development. Cadherins mediate cell–cell interactions, and integrins allow cells to remain
attached to the extracellular matrix.
         a. N-cadherin plays a specific role in differentiating cells of the nervous system from
ectodermal cells. Ectodermal cells express E-cadherin, but neural cells express N-cadherin. The
difference in cell-surface cadherins means that the neural cells lose their contact with the
surrounding ectodermal cells and establish new contacts with other neural cells. In the absence of
N-cadherin, the nervous system would not form. If you assume that E-cadherin expression is also
lost (as would occur normally in development) then these cells would lose all cell–cell contacts
and would probably undergo apoptosis.
         b. Integrins mediate the connection between a cell and its surrounding environment, the
extracellular matrix (ECM). The loss of integrins would result in the loss of cell adhesion to the
ECM. These cells would not be able to move and therefore, gastrulation and other developmental
processes would be disrupted.
         c. Integrins function by linking the cell’s cytoskeleton to the ECM. This connection is
critical for cell movement. The deletion of the cytoplasmic domain of the integrin would not
affect the ability of integrin to attach to the ECM, but it would prevent the cytoskeleton from
getting a “grip.” This deletion would likely result in a disruption of development similar to the
complete loss of integrin.

								
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