Which go these observations gives the most support to the endosymbiotic theory for the origin of eukaryotic cells?
a. the existence of structural and molecular differences between the plasma membranes of prokaryotic and the internal membranes of mitochondria and chloroplasts
b. the similarity in size between the cytosolic ribosomes of prokaryotes and the ribosomes within mitochondria and chloroplasts
c. the size disparity between most prokaryotic cells and most eukaryotic cells
d. the observation that some eukaryotic cells lack mitochondria
Ans: a. the existence of structural and molecular differences between the plasma membranes of prokaryotic and the internal membranes of mitochondria and chloroplasts
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If a virus enters the lytic phase in a host's cell, it will cause the host cell to
A. reject the virus. B. shrink because of the loss of cytoplasm that has been used in the synthesis of viral DNA. C. lysis due to the action of enzymes D. replicate itself at a higher than normal frequency. E. initiate an attack on the virus.
A woman with normal blood clotting mates with a man who has hemophilia. Their first child is a boy
who has hemophilia. Tests show that the father and son both have the same form of hemophilia, that it is X-linked, and that the boy has normal genetic inheritance. You can predict that if the couple produces more children together, then the odds are that
a. all of the children will have hemophilia. b. half of the boys and none of the girls will have hemophilia. c. none of the rest of children should have hemophilia. d. all of the boys and half of the girls will have hemophilia. e. half of the boys and half of the girls will have hemophilia.
Prolactin
a. stimulates the mammary glands to produce milk. b. causes the development of breasts and other secondary sexual characteristics in the male. c. acts in concert with FSH to produce milk. d. has secondary effects on reducing the size of the uterus after birth. e. is secreted only after the flow of milk has begun after delivery of the child.
Calcium levels in the body are maintained by hormones. If the blood calcium level rises above a set point, calcitonin is secreted by the thyroid gland and sets into motion responses to lower the blood calcium back to the set point
If the blood calcium level falls below a set point, the parathyroid gland secretes parathyroid hormone that sets into motion responses to raise the blood calcium. These homeostatic responses are examples of A) positive feedback. B) effectors. C) sensors. D) negative feedback.