What happens during gastrulation?
A. Cells migrate to form a layered structure.
B. A fertilized egg divides mitotically to form a
ball of cells.
C. A gastrula is transformed into a blastula.
D. The embryo divides into distinct zones of
cell division, cell expansion, and cell
differentiation.
E. All of these events happen during
gastrulation.
A
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Sea otters are protected from the cold by having:
a. thick blubber. b. thick fur. c. waxy fur. d. fatty tissue. e. thick skin.
Which of the following pairs indicates the closest
macroevolutionary link among the animals according to the evolutionary history tree in the text? a. flatworms; roundworms b. sponges; cnidarians c. arthropods; annelids d. arthropods; roundworms e. echinoderms; mollusks
Which of the following parts of an amino acid vary among different amino acids?
A. the carboxyl group B. the side chain, or R group C. the amino group D. the hydrogen on the central carbon
Helicobacter pylori can grow in the stomach because it
A) hides in macrophages. B) makes a capsule. C) possesses an enzyme that neutralizes HCl. D) makes HCl. E) invades epithelial cells.