Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 19
Test Yourself Questions
1. The process whereby a cell’s morphology and function has changed is called
a. determination.
b. cell fate.
c. differentiation.
d. genetic engineering.
e. both a and c.
Answer: c. Differentiation is the actual alteration of a cell’s morphology and physiology. Determination is
the process that determines what type of differentiation a cell will undergo.
2. Pattern formation in plants is along the __________ axis.
a. dorsoventral.
b. anteroposterior.
c. right-left.
d. root-shoot.
e. all of the above.
Answer: d. The first three choices describe the axes involved in animal development. Plant development
occurs along the root-shoot axis and in a radial pattern.
3. Positional information is important in determining the destiny of a cell in a multicellular organism.
Cells respond to position information by
a. dividing.
b. migrating.
c. differentiating.
d. undergoing apoptosis.
e. all of the above.
Answer: e. Cells may respond to positional information by all four processes.
4. Morphogens are
a. molecules that disrupt normal development.
b. molecules that convey positional information.
c. mutagenic agents that cause apoptosis.
d. receptors that allow cells to adhere to the extracellular matrix.
e. both a and c.
Answer: b. Morphogens are molecules that impart positional information and promote developmental
changes at the cellular level.
5. What group of molecules plays a key role in controlling the program of developmental changes?
a. motor proteins
b. transporters
c. transcription factors
d. restriction endonucleases
e. cyclins
Answer: c. A hierarchy of transcription factors is involved in the program that determines developmental
changes.
6. Using the list of events below, determine the proper sequence for the events of animal development.
1. Formation of tissues, organs, and other body structures in each segment.
2. Axes of the entire animal are determined.
3. Cells become differentiated.
4. The entire animal is divided into segments.
a. 2, 3, 4, 1
b. 1, 2, 4, 3
c. 2, 4, 3, 1
d. 3, 2, 4, 1
e. 2, 4, 1, 3
Answer: e. In animal development, the plan progresses from large to small.
7. The homeotic genes in Drosophila
a. determine the structural and functional characteristics of different segments of the developing
fly.
b. encode motor proteins that transport morphogens throughout the embryo.
c. are dispersed apparently randomly throughout the genome.
d. are expressed in similar levels in all parts of the developing embryo.
e. both a and c.
Answer: a. Homeotic genes produce transcription factors that regulate the gene expression in the
different segments thereby determining the structural and functional characteristics of each segment.
8. Which of the following genes do not play a role in the process whereby segments are formed in the
fruit fly embryo?
a. homeotic genes
b. gap genes
c. pair-rule genes
d. segment-polarity genes
e. All of the above play a role is segmentation.
Answer: a. Homeotic genes do not cause segments to form in the embryo. After the segments form,
they cause a segment to develop certain characteristics. Gap genes, pair-rule genes, and segmentpolarity genes are all types of segmentation genes that function during Phase 2 of development.
9. A type of stem cell that can give rise to any type of cell of an adult organism but cannot produce an
entire, intact individual is called
a. totipotent.
b. pluirpotent.
c. multipotent.
d. unipotent.
e. antipotent.
Answer: b. Embryonic cells are pluripotent, meaning these cells can produce nearly all types of
differentiated cells, but have lost the ability to produce an entire individual.
10. During plant development, the leaves and the flowers of the plant are derived from
a. the central region.
b. the basal region.
c. the suspensor.
d. the apical region.
e. both a and d.
Answer: d. The apical region gives rise to the leaves and flowers.
Conceptual Questions
1. Define development.
In biology a series of changes in the state of a cell, tissue, organ, or organism; the underlying process
that gives rise to the structure and function of living organisms.
2. Explain the hierarchy of gene expression that controls segmentation in Drosophila.
Answer: Maternal effect genes activate gap genes which, in turn, activate pair-rule genes which control
segment-polarity genes.
3. What are two characteristics of the proteins that are encoded by homeotic genes that give clues to
their function?
Answer: Homeotic proteins have a domain that binds to DNA and a domain that activates transcription.
Homeotic proteins activate transcription of specific genes that promote developmental changes in the
animal.
Experimental Questions
1. What was the goal of the research conducted by Davis, Weintraub, and Lasser?
Answer: The researchers were interested in the factors that cause cells to differentiate. For this
particular study, the researchers were attempting to identify genes involved in the differentiation of
muscle cells.
2. How did Davis, Weintraub, and Lasser’s reaserch identify the candidate genes for muscle
differentiation?
Answer: Using genetic technology, the researcher compared the gene expression in cells that could
differentiate into muscle cells to the gene expression in cells that could not differentiate into muscle
cells. Though many genes were expressed in both, the researchers were able to isolate three genes
that were expressed in muscle cell lines that were not expressed in the non-muscle cell lines.
3. Once the researchers identified the candidate genes for muscle differentiation, how did they test the
effect of each gene on cell differentiation? What were the results of the study?
Answer: Again, using genetic technology, each of the candidate genes was introduced into a cell that
normally did not give rise to skeletal muscle. This procedure was used to test whether or not these
genes played a key role in muscle cell differentiation. If the genetically engineered cell gave rise to
muscle cells, the researchers would have evidence that a particular candidate gene was involved in
muscle cell differentiation. Of the three candidate genes only one was shown to be involved in muscle
cell differentiation. When the MyoD gene was expressed in fibroblasts, these cells differentiated into
skeletal muscle cells.
Collaborative Questions
1. Discuss four types of cellular responses that cells can exhibit in response to positional information.
Answer: In multicellular organisms, cells are not independent from each other; they communicate and
influence each other. The result of this can vary widely depending on the position and type of cell. One
of the results is cell division. Second, positional information in animals may cause the migration of cells
or groups of cells in a particular direction from one region of the embryo to another. Third, it may cause
a cell or a group of cells to differentiate into a specific cell type. Finally, a cell's position and interaction
with other cells may promote cell death, which is also known as apoptosis.
2. Discuss meristems in plants.
Answer: In plants, there are organized groups of cells which are very active with respect to cell division
and producing stem cells. These areas are called meristems. At these areas, cells divide and retain the
ability to differentiate into several different types of cells. In plants there are two major places where
these meristems are found. First, meristem tissue found in the roots is called the root meristem, which
gives rise to the roots and tissue associated with the roots. The second is the shoot meristem which
produces all of the aerial parts of the plant such as stems, leaves and flowers.