Describe the major changes in the embryo during the first trimester
What will be an ideal response?
After blastulation and gastrulation, organogenesis first begins with development of the nervous system. Blood vessels and blood cells develop. Limb buds are present, and the gastrointestinal tract begins to form, although it is not functional. Nutrients and oxygen are obtained via the placenta. At about 9 weeks, skeletal elements form. The fetus can then move, a pulse is detectable, and although it is not externally detectable, the sexual organs have begun to form.
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Sturtevant's detailed mapping studies of the X chromosome of Drosophila supported what genetic principle?
A) That genes are arranged in a linear order on the chromosomes. B) That genes are carried on chromosomes. C) That sex determination is controlled by the X and Y chromosomes. D) That segregation of an allelic gene pair is accompanied by disjunction of homologous chromosomes. E) That different pairs of chromosomes assort independently.
In a surgery of a few hours, the skeletal muscles are normally immobilized. Using the knowledge of this chapter, which of the following conditions would most likely result normally if countermeasures were not taken?
A) excessive redness of the skin B) fluid buildup in the tissues C) excessive sweating D) rapid breathing
Which of the following describes primary succession?
a. succession on land that previously had no life
b. succession that moves a community away from equilibrium
c. succession in response to a natural disturbance
d. succession characterized by equilibrium
The response of plants to touch is called ________.
Fill in the blank(s) with the appropriate word(s).