What is the immune function of the placenta in human embryonic development?
What will be an ideal response?
ANSWER: The placenta prevents fetal blood from entering the maternal bloodstream. The fetal blood
circulation system remains closed, and nutrients and oxygen from the mother’s circulation
pass into the circulation of the embryo by diffusion. Since the maternal and fetal blood
circulations do not directly mix, this prevents the mother from developing an immune
reaction against cells of the embryo, which, because it is genetically different from the
mother, may be recognized as foreign by the mother’s immune system.
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Which of the following statements about cancer is FALSE?
A. It is characterized by uncontrolled cell division. B. Over 1 million Americans are diagnosed with cancer each year. C. Most cancers involve genetic changes that are passed from parent to offspring. D. At least 80% of all human cancers are related to exposure to carcinogens. E. It is caused by an accumulation of mutations.
The tip of the stem (the shoot tip) contains the
a. apical meristem. b. lateral meristem. c. intercalary meristem d. lateral buds. e. endodermis.
In the illustration above showing the haploid phase in the life cycle of a fern, what part represents the male
gametangium? a. 1 b. 2 c. 3 d. 4 e. 5
What percentage of human DNA is devoted to coding exons?
a. 1% b. 1.5% c. 25% d. 50% e. 100%