Grand Rapids variety of lettuce produces seeds that will not germinate unless they are exposed to light
Phytochrome is also involved in that exposure to red light stimulates germination and far-red light
inhibits germination. However, the effect of red light can be reversed by an immediate exposure to farred
light--and vice versa. You design an experiment in which you expose seeds of Grand Rapids
lettuce first to red light, then immediately to far-red light, and then immediately to red light again.
Would these seeds germinate? Use your knowledge of the phytochrome molecule to explain your
reasoning. What if the seeds were exposed first to red light, then immediately to far-red light, then
immediately to red light again, and then immediately to far-red light again What will be an ideal response?
Concepts to Consider: Phytochrome exists in two interconvertible forms: Pr and Pfr. Exposure to red
light converts Pr to Pfr, which is the active form and thus stimulates germination. However, if the
exposure to red light is followed immediately by an exposure to far-red light, Pfr will be converted
back to Pr before germination is stimulated, and the seeds will not germinate. Using this reasoning, the
result will depend on which wavelength the seeds receive last.
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Which of the following statements about double fertilization in angiosperms is correct?
A) One pollen grain combines with the egg to form the zygote, and one pollen grain combines with the polar nuclei to form endosperm. Two sperm combine with a polar nucleus to form endosperm. B) Two pollen grains combine with two ovules to form the zygote and endosperm. C) One sperm combines with the polar nuclei to form the zygote, and one sperm combines with the egg to form endosperm. D) One sperm combines with the egg to form the zygote, and one sperm combines with the polar nuclei to form endosperm.
Which of the following is/are MHC class I genes?
A) HLA-A B) HLA-B C) HLA-C D) HLA-A, HLA-B, and HLA-C
How does the release of histamine by mast cells help the innate immune response?
A. It signals neutrophils to migrate to the site of infection. B. It makes it easier for neutrophils to move from the bloodstream to the site of infection. C. It increases the volume of blood flow in the area of the infection. D. Two answer options are correct: It makes it easier for neutrophils to move from the bloodstream to the site of infection AND increases the volume of blood flow in the area of the infection.
Recent discoveries of microscopic fossils have extended the known history of life to about:
A. 1 billion years ago. B. 4.5 billion years ago. C. 3.5 billion years ago. D. 2 billion years ago.