Biology 115, Quiz 4: Answer Key

A.

• 1. (c)
• 2. (c)
• 3. (e)
• 4. (c) (award 0.1 point to "e")
• 5. (b)
• 6. (c) (award 0.2 points to "e")

B.

• 7. nucleic acid and protein
  (give full credit if "genetic material" is substituted for "nucleic
  acid"; give 0.2 points for "RNA" or "DNA")
• 8. embryonic and chorion
• 9. free radicals

*** Note: there is no problem 10 ***

C.

• 11. antibiotic: A drug that interferes with bacterial growth or survival, typically by inhibiting a bacterial enzyme.
  (full credit if antibacterial activity is mentioned, even if enzyme inhibition is not. 0.3 points for
  mentioning inhibiting enzymes if bacteria aren't specified as the targets).
• 12. morphogenesis: development of the shape of the growing embryo or fetus.
  (full credit requires use of the word "shape" or a close synonym; partial credit for recognizing that it is an aspect of embryonic development).
• 13. episiotomy: a minor surgical procedure during childbirth in which the vaginal orifice is widened with an incision to prevent tearing.

NOTE THAT THERE ARE TWO PROBLEMS NUMBERED 13
D.

• 13.

blastula	morula	zygote	neurula	gastrula
3	2	1	5	4

(Give up to 0.6 for partially correct sequences, e.g. one pair backward.)

• 14.

muscles	skin epidermis	pancreas	bone,cartilage	nervous system
mesoderm	ectoderm	endoderm	mesoderm	ectoderm

(0.2 points each, of course)

E.

15. One might expect a single cell from the 4-cell embryo to develop into a complete animal, whereas a single cell from an 8-cell embryo probably would not. This is because all the components of the original zygote's cytoplasm are divided more or less equally among the four cells found at the end of the second mitotic division, whereas material from only one pole wind up in any of the eight cells found at the end of the third mitotic division. Thus essential developmental components are likely to be absent from the single cell from the 8-cell embryo, and it is unlikely to be able to develop into a complete animal.

(One point for getting the basic fact right--that the cell from the 4-cell embryo is probably viable and the cell from the 8-cell embryo isn't. Partial credit beyond that for sensible explanations).

16. The enzyme inhibited by AZT is reverse transcriptase; the enzyme inhibited by ritonavir is the viral protease [ or just protease ]. The multidrug therapy works better than a single drug because it attacks the viral life cycle at two different stages, so that the virus has a lowered likelihood of being able to mutate away from sensitivity to one of the drugs while it is fighting off the other challenge.

(One point for getting the enzyme names right; be generous in giving credit for explaining why the multidrug therapy works)