The location of the placenta is
A. in the vagina.
B. at the cervix of the uterus.
C. lining the oviduct.
D. in the uterus.
D. in the uterus.
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It takes very few molecules of a hormone to cause changes in a target cell. This may be explained by the fact that: (Select all correct answer options.)
A. transcriptional activation produces many copies of mRNA, each of which is translated many times. B. the mechanism of hormonal action involves the replication of the hormone within the target cell to quickly magnify the hormone's effect. C. hormones are large molecules that persist for years and can repeatedly stimulate the same cell. D. the mechanism of hormonal action may involve an enzyme cascade that amplifies the response to a hormone. E. the mechanism of hormonal action involves memory cells that have had prior contact with the hormone and immediately respond to its presence.
The route followed by a sperm from production to fertilization in a flowering plant is:
A. A pollen grain is produced in the anther, transported to a stigma where it produces two sperm cells that pass through a pollen tube that grows down the style to the ovary. One of the sperm cells enters the ovule and joins with the egg cell. B. A pollen grain is produced in the pistil, which explosively ejects it into the air where it is transported to a stigma where it forms two sperm cells. One of the sperm cells passes through a pollen tube that grows down the style to the ovary, enters the ovule and joins with the egg cell. C. A sperm cell, enclosed in a pollen grain with another sperm, is produced in the filament, transported to a stigma where it passes through a pollen tube that grows down the style to the ovary, enters the ovule and joins with the egg cell. D. A sperm cell, enclosed in a pollen grain with another sperm, is produced in the anther, transported to the pedicel where it passes through a pollen tube that grows down the style to the ovary, enters the ovule and joins with the egg cell. E. A sperm cell is produced in the anther, transported to a stigma where it becomes enclosed along with another sperm cell into a pollen grain that grows down the style to the ovary, enters the ovule and joins with the egg cell.
All the different kinds of RNA are transcribed in the
a. mitochondria. b. cytoplasm. c. ribosomes. d. nucleus. e. endoplasmic reticulum.
Classification. Respond to the following statements with reference to the five types of white cells listed below.
A. These cells scavenge dead cells and attack bacteria directly. B. These cells recognize cell surface antigens and initiate the proliferation of lymphocytes. C. Antibody production occurs in these cells. D. These cells destroy cells infected by viruses. E. These cells kill tumor cells but are not B or T lymphocytes.