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Return to Principles of Development 6e Student Resources
Chapter 12 Self-test questions
Growth, post-embryonic development and regeneration
In developmental biology, what is meant by the concept of "growth"?
Growth occurs through increases in cell size.
Growth occurs through increases in cell number.
Growth can result from increases in the volume of extracellular matrix between cells.
All of the above are mechanisms by which growth occurs.
What will be the result of grafting a limb bud from a large species of the salamander
onto a smaller species?
The grafted bud will be unable to grow in a smaller animal, and will be lost.
The grafted bud will grow to a size appropriate to its host, and will thus be of the same size as the other limbs.
The grafted bud will grow to become a larger limb than the others, reflecting its origin in the larger species.
The grafted bud will initially grow larger than the others, but with time will regulate and become a limb of the same size as the other limbs of its host.
Many cells in the body divide only rarely, if at all; neurons, red blood cells, and keratinocytes are extreme examples. In which portion of the cell cycle would such cells be considered to be?
The size of a cell is generally controlled by the amount of DNA in the nucleus: the more DNA, the larger the cell. What do animals in which the amount of DNA is naturally doubled, such as tetraploid salamanders, tell us about growth control?
The animals grow to a normal size, and contain only half as many cells, indicating that growth is regulated at the level of absolute size, rather than cell number.
The animals grow to twice the normal size, indicating that growth is regulated at the level of the number of cells present.
The animals end up with cells that are twice as big, but only half as many, resulting in an animal that is half its normal size, indicating that the number of cells is the critical determinant of growth.
The animals grow to a normal size, and contain only half as many cells, indicating that growth is regulated by the total amount of DNA present in an organism.
Cancer is believed to often arise from stem cells, rather than fully differentiated cells. Which of the following is consistent with this view?
Stem cells are actively dividing and express few differentiated functions, so they may have fewer changes to undergo than do fully differentiated cells in becoming cancer cells.
DNA replication is necessary for mutations to occur, and stem cells are replicating their DNA whereas differentiated cells are for the most part not replicating their DNA.
Stem cells require genes such as Wnt for the maintenance of their stem cell function, and many such genes can also function as oncogenes.
All of the options given are reasons that cancer cells may more readily arise from stem cells than from fully differentiated cells.
Which of the following statements is true?
The genes involved in cancer are all classed as oncogenes.
All genes involved in cancer are of a class called tumor suppressor genes.
Both oncogenes and tumor suppressor genes are involved in cancer.
No unifying classifications can be applied to the genes involved in cancer.
Disease, injuries, and birth defects that compromise the function of the pituitary may lead to decreased stature (height). What treatment might be prescribed, and what would be its rationale?
Since the pituitary is damaged or missing, the only possible treatment would be the transplantation of a donor pituitary.
Loss of pituitary function could lead to decreased growth hormone production, and hence short stature; recombinant human growth hormone might be prescribed.
Since the pituitary is responsible for secretion of luteinizing hormone and follicle stimulating hormone, both of which are required for normal fertility, replacement therapy with these hormones may be prescribed for fertility problems, but no therapy would be possible for the short stature.
Since growth hormone controls growth hormone releasing hormone and somatostatin production in the hypothalamus, its absence would be compensated for by administration of those hormones.
Growth is stimulated by which of the following signaling molecules?
IGF-1 and -2
Ossification in the long bones in vertebrates starts in the
Adult human bone:
grows only at the extreme ends (epiphysis)
grows only in the center (diaphysis)
grows only at the growth plates between the epiphysis and the diaphysis
grows throughout its length
What are osteoblasts?
Osteoblasts are the stem cells that give rise to chondrocytes.
Osteoblasts are maturing chondrocytes, capable of secreting the cartilage present in the growth plate.
Osteoblasts are enlarged chondrocytes present in the hypertrophic zone of the growth plate.
Osteoblasts are bone-forming cells that derive from stem cells in the bone marrow, and therefore have no lineage relationship to chondrocytes.
Molting in insects and other arthropods is triggered by
Metamorphosis in amphibians is triggered by environmental cues that act on the:
Epimorphosis is regeneration through
repatterning of existing cells without a requirement for new growth, as occurs in
repatterning of existing cells without a requirement for new growth, as occurs in newts
the reinitiation of division in existing cells and new growth, followed by patterning, as occurs in newts
the reinitiation of division in existing cells and new growth, followed by patterning, as occurs in
When the blastema forms after amputation of a newt limb, what processes must the cells undergo in order for regeneration to occur?
The cells must simply dedifferentiate in order for regeneration to occur.
The overlying wound epidermis takes on a role similar to that of the apical ectodermal ridge in normal limb development, and limb regeneration can then occur.
Some cells in the blastema will transdifferentiate after amputation, and this allows regeneration to proceed.
Formation of an apical ectodermal cap, dedifferentiation, cell division and redifferentiation are all involved.
Is regeneration in
similar to regeneration in vertebrates, or is it fundamentally different in some way?
occurs through a repatterning of existing cells by morphallaxis, unlike regeneration in vertebrates, which occurs through epimorphosis.
occurs through the reinitiation of cell division in existing cells, followed by repatterning of those cells, very much like regeneration in vertebrates.
occurs through the reinitiation of cell division in existing cells, followed by repatterning of those cells, which is totally different from regeneration in vertebrates.
occurs through the reinitiation of cell division in existing cells, followed by repatterning of those cells, whereas regeneration in vertebrates occurs through a process of repatterning of existing cells.
What molecular marker of head identity is found in the apical tip of a
during head regeneration?
Hox genes from the 3' (anterior) end of the
A bud characteristic of the budding region.
If the nerve supply to a newt limb is severed before amputation, how will this affect regeneration?
A blastema will form but will not grow, and regeneration will fail.
No regeneration occurs, and the stump heals over as it would in a mammal.
Outgrowth will occur, but the identity of the limb will be lost and normal proximo-distal patterning will not occur.
Regeneration of most tissues will occur normally, but regeneration of the nerves will not occur.
What is the result of grafting a blastema derived from a distal amputation onto a stump that has been amputated at a proximal position?
The distal blastema is unable to properly interpret its positional values in this circumstance, and regeneration fails.
The distal blastema regenerates the entire limb, supplying all the cells required for this regeneration.
The distal blastema regenerates the limb regions removed in the distal amputation, resulting in a shortened limb missing the regions between the proximal and distal amputation sites.
The limb regions between the distal and proximal amputation sites are filled in by intercalary growth from the proximal stump, and the regions distal to the distal amputation are regenerated from the distal blastema.
How does the dose-dependence of retinoic acid treatment support the notion that a gradient of retinoic acid can act as a morphogen along the proximo-distal axis in the limb?
Treatment with high levels of retinoic acid causes a proximal blastema to be respecified as a distal blastema, and only distal structures are regenerated.
Treatment with high levels of retinoic acid causes any blastema to form only distal structures.
Treatment with high levels of retinoic acid causes any blastema to be respecified as a proximal blastema, but it will form only proximal structures.
Treatment with high levels of retinoic acid causes a distal blastema to be respecified as a proximal blastema, and regeneration of a full limb may be initiated from proximal values.
What is especially exciting about research into regeneration in zebrafish?
Amputation of a fin leads to regeneration of a limb, implying an evolutionary homology between the two structures.
Removal of the eye results in regeneration of the eye, and since zebrafish and humans have very similar eyes, this research may lead to new therapies for eye damage in humans.
Limited regeneration of heart muscle can occur in zebrafish, and the ability to study zebrafish genetically will enhance our ability to understand the genetic basis of regeneration.
Regeneration of the heart muscle does not occur in either humans or zebrafish, but experiments can be done on zebrafish that cannot be done on humans, opening up a model system in which to study heart regeneration for use in humans.
Which signaling pathway seems to have a role in aging in animals as different as worms and mice?
Which of the following is consistent with a model of aging in which stresses leading to DNA damage cause senescence?
Werner's syndrome is a premature aging illness, possibly caused by a defect in DNA repair.
Dietary restriction in mammals reduces the production of DNA-damaging free radicals in the mitochondria.
Senescent cells in culture that have stopped dividing often express p21 and p16, proteins that are normally activated in response to DNA damage.
All of the options given are consistent with a model of aging based on DNA damage.
What does it tell us about aging that cells from different organisms are capable of a fixed number of divisions in culture, and that the number of divisions reflects the relative life span of the organism?
The cells from these different organisms are not all equally adapted to growth in culture.
In each organism, the cells seem to be capable of a genetically determined number of divisions, after which the organism undergoes senescence and dies.
Cells growing in culture live for the same number of years that the organism from which they are derived would be expected to live, indicating a genetically determined life span.
The conditions cells encounter in culture lead to oxidative damage which reflects the kind of damage that normally leads to aging in the organism.
Puberty is initiated by the pulse release of _____________(hormone).
insulin-like growth factors
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