One difference between sieve-tube cells and vessels is that sieve-tube cells are ________, but vessels are dead.
A. more spherical
B. alive
C. nucleated
D. placed end to end
E. hollow
Answer: B
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Which one of the following statements is true of the 32 allele in the CCR5 gene? (Choose all that apply)
A. It codes for a mutant protein that is completely inactive. B. It leads to a deletion which maintains the reading frame. C. It provides some protection against HIV progression to AIDS in both its heterozygous and homozygous forms. D. It is an example of a beneficial mutation. E. It affects the attachment of HIV to an animal cell by altering one of the viral proteins.
The semicircular canals are:
a. empty b. filled with gas c. filled with a liquid d. small bones in the ear e. passageways for nerves
IR absorbed by a molecule causes its bonds to break.
a. true b. false
The electrons excited by sunlight in photosystem I are replaced by ________, and the electrons excited by sunlight in photosystem II are replaced by ________
A) electrons from water; electrons from water B) electrons from water; electrons from photosystem I C) electrons from water; electrons from carbon dioxide D) electrons from photosystem II; electrons from water E) electrons from carbon dioxide; electrons from water