A difficult task for the biologist trying to determine if a group of organisms is a separate species is __________.
a. to compare appearances of different organisms
b. to determine if a hybrid offspring is produced
c. exposing isolating mechanisms
d. determining whether group members breed with organisms outside the group
e. comparing DNA from those
Ans: d. determining whether group members breed with organisms outside the group
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Which one of the following describes a tRNA molecule that specifically recognizes the codon for the amino acid histidine, but is covalently bound (charged with) to the amino acid serine?
A. histinyl-tRNASer B. histinyl-tRNAHis C. seryl-tRNASer D. seryl-tRNAHis
Match the following items with the correct phrases.
_______1. A monomer; the most common type of immunoglobulin; very high levels are produced in the secondary (anamnestic) response to an antigen. _______2. A pentamer; five monomers linked together by a J-chain; the first type of immunoglobulin to be formed in the primary response to an antigen. _______3. A monomer; present on the surface of mast cells and basophils. _______4. A dimer; two monomers linked together by a J-chain; frequently found in mucous membranes. _______5. Produced by atopic individuals in response to allergens. a. IgA b. IgD c. IgE d. IgG e. IgM
Steroid hormones generally function by ________
a. being released by certain cells and affecting only the cells in close proximity to the source b. binding to receptors on the plasma membrane and triggering cAMP formation inside the cell c. entering target cell nuclei, binding to receptors and affecting gene transcription d. diffusing across the synaptic cleft and binding to receptors on postsynaptic neurons
During a menstrual cycle, a midcycle surge of _____ triggers ovulation
a. estrogens c. LH b. progesterone d. FSH