When a steroid hormone and a peptide hormone exert similar effects on a population of target cells, then _____
A) the steroid and peptide hormones must use the same biochemical mechanisms
B) the steroid and peptide hormones must bind to the same receptor protein
C) the steroid hormones affect the synthesis of effector proteins, whereas peptide hormones activate effector proteins already present in the cell
D) the steroid hormones affect the activity of certain proteins within the cell, whereas peptide hormones directly affect the processing of mRNA
E) the steroid hormones affect only the release of proteins from the target cell, whereas peptide hormones affect only the synthesis of proteins that remain in the target cell
Answer: C
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A. hotspot B. habitat loss C. edge effects D. megafaunal extinction E. extinction vortex
Prezygotic mechanisms lead to reproductive isolation by preventing the formation of
A. mating pairs. B. fertile eggs. C. fertile sperm or pollen cells. D. somatic cells. E. hybrid zygotes.
Research has shown that cytokinin levels fluctuate seasonally in temperate plants. What season would you expect to see the lowest levels of cytokinins and why would this be adaptive?
A. Spring, because lower levels of cytokinin allow auxin to promote rapid growth in stem height. This will allow the plant to compete effectively for sunlight. B. Winter, because lower levels of cytokinin will place buds into a dormant state. This will protect the underlying tissues from freezing until spring. C. Autumn, because lower levels of cytokinin at this time of year will induce the production of ethylene. This will result in maturation of fruit and ensure effective seed dispersal before winter. D. Summer, because lower levels of cytokinin would slow growth down and delay leaf aging. This will allow the plant to maximize the production of starch and increase it's sugar reserves. This will help ensure the plant's survival through autumn and winter.
Elastic cartilage is found in
a. the ends of long bones. b. the outer flaps of the ears. c. intervertebral discs. d. the trachea. e. the ribs.