Loading of most carbohydrates produced by photosynthesis into companion cells at a source occurs by ____
a. osmosis
b. proton pumping
c. suction from unloading at a sink
d. active transport
e. diffusion of water from the xylem
ANSWER: d
You might also like to view...
The openings in leaves that function to
exchange gases are called
a. cuticles. b. stomata. c. guard cells. d. pits. e. pores
Viruses that cause infection resulting in alternating periods of activity with symptoms and inactivity without symptoms are called ________.
A. prions B. delta agents C. viroids D. oncogenic E. latent
In the nineteenth century, prevailing beliefs came
into conflict with findings from all of these EXCEPT a. biogeography. b. comparative morphology. c. the fossil record. d. plate tectonics. e. global exploration.
Which of the following statements about the development of bone in humans is NOT true?
A. Bone breakdown and replacement occur throughout life. B. A primary ossification center forms in the middle of a long bone. C. A secondary ossification center forms at the end of a long bone. D. A cartilaginous disk remains between the primary and secondary ossification centers until old age. E. Bones may form within a cartilage model or within a membrane matrix.