Which structure or structures function to open and close the stomata?
a. cuticle
b. mesophyll
c. palisade cells
d. guard cells
e. chloroplasts
D
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Which of these best represents natural selection?
A) Recessive albinism is more common among the Hopi of Arizona than in the general population of the U.S. B) A gradual change in specific human mitochondrial DNA sequences occurs along the Nile river in Egypt. C) ABO blood type frequencies are similar in northern Africa, southern Spain, and the middle east. D) Lactose tolerant alleles are very prevalent in herding populations that drink milk as a staple.
When blood returns from the pulmonary circuit, it first enters which chamber of the heart?
a. left atrium b. left ventricle c. right atrium d. right ventricle e. both the left atrium and the right atrium
What is the process in which one activated receptor can give rise to thousands of
final products? a. signal transcription
b. signal transmission c. signal transduction d. signal termination e. signal amplification
The purpose of a mordant in the Gram stain is to
A) remove the simple stain. B) make the bacterial cells larger. C) make the flagella visible. D) prevent the crystal violet from leaving the cells. E) make gram-negative cells visible.