What is the cause of the massive amount of programmed cell death of nerve cells (neurons) that occurs in the developing vertebrate nervous system, and what purpose does it serve?
What will be an ideal response?
Immature neurons are produced in excess of the number that will eventually be required. They compete for the limited amount of survival factors secreted by the target cells they contact. Those cells that fail to get enough survival factor undergo programmed cell death. Up to half or more of the original nerve cells die in this way. This competitive mechanism helps match the number of developing nerve cells to the number of target cells they contact.
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An agricultural worker is punctured by a tool used in the field. An infection, characterized by the development of a papule that is similar to a cauliflower appearance, develops. The worker is most likely suffering from which type of infection?
a. Mycetoma b. Chromoblastomycosis c. Tinea nigra d. Black piedra
Canada geese have become a major source of Giardia and Cryptosporidium contamination of soil and fresh water.
Answer the following statement true (T) or false (F)
Variation in which of the following is not a major mechanism for regulation of blood pressure?
1.cardiac output 2.constriction of blood vessels 3.pacemaker signal strength 4.total blood volume
At Hardy - Weinberg equilibrium, allele frequencies
A. Change from one generation to the next so evolution does not occur B. Remain constant from one generation to the next so evolution does not occur C. Change from one generation to the next so evolution occurs D. Remain constant from one generation to the next so evolution occurs E. None of the answers are correct