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Question 1

In developmental biology, what is meant by the concept of 'growth'?

a) Growth occurs through increases in cell size.

b) Growth occurs through increases in cell number.

c) Growth can result from increases in the volume of extracellular matrix between cells.

d) Cell death is an important determinant of overall growth.

e) All of the above are mechanisms by which growth occurs.

Question 2

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?

a) M phase

b) G1 phase

c) G0 phase

d) S phase

e) G2 phase

Question 3

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 experiments in which the amount of DNA is doubled (tetraploidy in salamanders) tell us about growth control?

a) 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.

b) The animals grow to twice the normal size, indicating that growth is regulated at the level of the number of cells present.

c) 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.

d) 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.

e) The animals form tadpoles that are twice as big as usual, but die during metamorphosis, indicating that the abnormal ploidy is incompatible with adult survival.

Question 4

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?

a) Since the pituitary is damaged or missing, the only possible treatment would be the transplantation of a donor pituitary.

b) Loss of pituitary function could lead to decreased growth hormone production, and hence short stature; recombinant human growth hormone might be prescribed.

c) 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.

d) 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.

e) Since the pituitary is located under the brain, above the roof of the mouth, no intervention is possible since this location is hard to reach.

Question 5

Adult human bone:

a) grows only at the extreme ends (epiphysis).

b) grows only in the center (diaphysis).

c) grows only at the growth plates between the epiphysis and the diaphysis.

d) grows throughout its length.

e) does not grow at all after maturity is reached.

Question 6

What are osteoblasts?

a) Osteoblasts are the stem cells that give rise to chondrocytes.

b) Osteoblasts are the proliferating precursors of the chondrocytes.

c) Osteoblasts are maturing chondrocytes, capable of secreting the cartilage present in the growth plate.

d) Osteoblasts are enlarged chondrocytes present in the hypertrophic zone of the growth plate.

e) Osteoblasts are bone-forming cells that derive from stem cells in the bone marrow, and therefore have no lineage relationship to chondrocytes.

Question 7

Cancer is believed to often arise from stem cells, rather than fully differentiated cells. Which of the following are consistent with this view?

a) 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.

b) 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.

c) Teratocarcinomas are tumors that arise from germ cells or embryonic stem (ES) cells, under certain circumstances, demonstrating that tumors can arise from stem cells without further mutation.

d) Stem cells require genes like Wnt for the maintenance of their stem cell function, and many such genes can also function as oncogenes.

e) All of the above are reasons that cancer cells may more readily arise from stem cells than from fully differentiated cells.

Question 8

Is there a difference between oncogenes and tumor suppressor genes?

a) Yes, oncogenes are genes that can cause cancer when they become mutated to become proto-oncogenes, whereas tumor suppressor genes play no role in cancer.

b) Yes, oncogenes prevent cancer from forming unless they are mutated to become proto-oncogenes, whereas tumor suppressor genes stimulate the formation of cancer even in the absence of mutation.

c) No, oncogenes and tumor suppressor genes both stimulate the development of cancer, even in the absence of their becoming mutated.

d) Yes, oncogenes are mutated versions of genes that promote abnormal cell division (such as ras and myc), whereas tumor suppressor genes are genes that normally hold cell division in check when it is not appropriate (such as Rb and p53).

e) No, since both types of genes contribute to the development of cancer, there is no difference between them.

Question 9

Insects such as Drosophila undergo three molts before becoming a pupa and undergoing metamorphosis. Molting, which is also called 'ecdysis', is controlled by what hormone?

a) ecdysone

b) juvenile hormone

c) auxin

d) cytokinin

e) growth hormone

Question 10

Metamorphosis of amphibians is triggered by environmental cues that act on the:

a) thyroid.

b) pituitary.

c) hypothalamus.

d) eye.

e) embryo.

Question 11

What does it tell us about aging that cells from different organisms are capable of a fixed number of divisions in culture, and that number of divisions reflects the relative life-span of the organism?

a) The cells from these different organisms are not all equally adapted to growth in culture.

b) In each organism, the cells seems to be capable of a genetically determined number of divisions, after which the organism undergoes senescence and dies.

c) 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.

d) The conditions cells encounter in culture lead to oxidative damage which reflects the kind of damage that normally leads to aging in the organism.

e) Conditions encountered by cells in culture are identical to the conditions encountered in vivo, so cells in culture undergo their normal aging program.

Question 12

Which of the following is consistent with a model for aging in which stresses leading to DNA damage cause senescence and aging?

a) The DAF-16 protein of C. elegans is involved in the activation of stress responses.

b) Dietary restriction in mammals reduces the production of DNA-damaging free radicals in the mitochondria.

c) Werner's syndrome is a premature aging illness, possibly caused by a defect in DNA repair.

d) All of the above are consistent with a model for aging based on DNA damage.

e) None of these observations has any relationship to a model for aging and senescence.

Oxford University Press, Online Resource Centre, Chapter 12.

Chapter 12

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