When pollen from one species lands on the stigma of a flower from another species
a. the pollen tube typically does not develop.
b. the pollen tube typically forms, but the sperm cannot penetrate the egg.
c. the pollen tube typically forms and grows to the ovary, but then stops.
d. the pollen tube typically forms, but the sperm are killed.
e. the pollen tube typically forms and the egg is usually fertilized, but the embryo rarely
grows.
A
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Which of the following factors likely contributed to the accumulation of O2 within Earth's atmosphere?
A. the evolution of cyanobacteria B. the fact that oxygen is also cycled during the carbon cycle C. the fact that there is a slight "de-coupling" between photosynthesis and respiration D. the fact that photosynthesis releases O2 as a product E. All of these answer options are correct.
As humans move into an area, the habitat often becomes fragmented due to clearing of land to
build homes and roads, while leaving small areas of natural habitat. For small species that cannot navigate long distances from one habitat fragment to the next, speciation will likely occur due to __________ barriers.
a. geographical b. temporal c. behavioral d. geographical and temporal
The same bees that pollinate the flowers of the Brazil nut trees also pollinate orchids, which are epiphytes (in other words, plants that grow on other plants); however, orchids cannot grow on Brazil nut trees. These observations explain _____
A) the coevolution of Brazil nut trees and orchids B) why Brazil nut trees do not set fruit in monoculture plantations C) why male orchid bees do not pollinate Brazil nut tree flowers D) why male orchid bees are smaller than female orchid bees
The Pax6 gene codes for a transcription factor that initiates differentiation of cells that ultimately form the eye. Suppose that a researcher added an activator for the Pax6 gene to embryonic cells that are in the process of forming legs in Drosophila
What do you think the researcher will observe? A) Legs and eyes will develop normally. B) Legs will develop where the eyes normally develop. C) Eyes will develop where the legs normally develop.