In 1999, researchers found that they could create hybrid embryos between two species of sea urchin that had been separated for 10 million years. By treating eggs to remove the jelly coat, the sperm of the other species was able to fertilize. What step of the fertilization process is normally blocked, preventing hybridization between these species?
A. Sperm penetration
B. Membrane fusion
C. Egg activation
D. Nuclear fusion
Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?
Gather Content
What do you already know about fertilization? What other information is related to the question?
Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
A. Sperm penetration
Clarify Question
What is the key concept addressed by the question?
· The concept addressed here involves the factors that must be dealt with for fertilization to occur.
What type of thinking is required?
· Analyze level:
o This is an analyze question because you have to break hybridization and fertilization into their component pieces to understand how they function.
Gather Content
What do you already know about fertilization? What other information is related to the question?
· For fertilization to occur, sperm must first find and recognize an egg.
· Once recognition occurs, sperm must use digestive enzymes that are kept in their acrosomal region to break through the layers around the egg.
· Digestive enzymes that work for one species may not work to penetrate the layers of the egg of another species.
Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
· Since removing the jelly coat allowed the sperm to fertilize the egg, it appears that that was the only barrier to fertilization. Thus, penetration of sperm into the egg was the step that was blocked.
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
· Analyze level:
o Answering this question correctly depended not only on distinguishing between fertilization and hybridization, but on your ability to break down, or analyze, factors that prevent fertilization. If you got an incorrect answer, did you remember that components of fertilization include the possession of digestive enzymes that are used to penetrate the egg, or that the enzymes of one species may not work for another species?
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Mutations in the DFNA20/26 locus, which codes for the actin gamma 1 protein, are associated with congenital deafness. An irate senator complains that government money is being wasted on studies of this mutant gene -- in yeast! "I am no biologist," says the senator, "but I am pretty sure yeast don't have ears." How do you respond?
A. "You are right, Senator -- yeast do not have ears. We should revoke the funding immediately." B. "We can learn valuable information about the structure of the mutant protein by expressing it in yeast. It is difficult to collect large amounts of actin from tiny hair cells, and unethical to collect it from human patients." C. "We can learn valuable information about the transcription of the mutant gene in yeast. It is much more difficult to study transcription in human cells." D. "We can learn valuable information about sound transmission through the mutant yeast. By placing a speaker against a yeast vial and recording sound from the other side, we can infer how the mutant actin affects sound waves." Clarify Question What is the key concept addressed by the question? What type of thinking is required? Gather Content What do you already know about mutant genes? What other information is related to the question? Choose Answer Given what you now know, what information is most likely to produce the correct answer? Reflect on Process Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
Where in the brain is the corpus callosum?
a. between the cerebellum and the medulla oblongata b. below the cerebellum c. between the two hemispheres of the cerebrum d. between the pons and the midbrain e. between the thalamus and the hypothalamus
What gland secretes growth hormone?
A) posterior pituitary B) anterior pituitary C) adrenal cortex D) thyroid gland
By the end of which period, characterized by warming climate and increased oxygen in the seas, did a dramatic adaptive radiation occur, giving rise to all major animal lineages?
A. Devonian B. Proterozoic C. Cambrian D. Jurassic E. Ediacaran