How many mass extinctions have been identified during the history of life on Earth?
A. none
B. four
C. one
D. six
E. five
Answer: E
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Cytotoxic T cells destroy target cells by
A. the CD95 pathway. B. the perforin pathway. C. direct killing mediated by activated oxygen species. D. both direct killing mediated by activated oxygen species and the perforin pathway. E. both the perforin pathway and the CD95 pathway.
Ian and Bryony are both carriers for two autosomal recessive disorders, PKU (chromosome 12) and cystic fibrosis (chromosome 7). They are expecting a daughter. What is the probability that she will have PKU but not CF?
A) 9/16 B) 3/16 C) 1/2 D) 1/16
When you are upright, what is the primary mechanism that propels blood in your feet back to your inferior vena cava?
A. recoil of elastic fibers in the walls of the leg veins B. contraction of the left ventricle of the heart C. contraction of smooth muscle in the walls of the leg veins D. contraction of skeletal muscles in your legs E. the valves in the leg veins alternating between open and closed
Describe what is known about mtDNA replication and segregation
What will be an ideal response?