Why do sieve elements require companion cells?
What will be an ideal response?
As a sieve element matures, it loses most of its organelles, including the nucleus, Golgi bodies, and almost all of its ribosomes. The sieve elements need companion cells to stay alive. Each sieve element has an associated companion cell that arises by division of the same parent cell. The companion cell retains its nucleus and other components. Many plasmodesmata connect the cytoplasm of the two cells, so the companion cell can provide all metabolic functions necessary to sustain its paired sieve element —for decades, in some cases.
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DNA replication involves the synthesis of an RNA primer on one strand of the DNA
Indicate whether the statement is true or false.
In a plant, __________ represent a source and __________ represent a sink
a. leaves; fruits b. fruits; leaves c. roots; leaves d. roots; fruits
Up until the late eighteenth and early nineteenth centuries, many naturalists believed that all species of living organism(s) had been created separately and had remained unchanged since the creation. Around that time, scientific research provided findings that were contradictory to that idea. All of the following are findings that contradict the idea of a single creation. Choose the exception
a. As scientists explored more of the earth, they found that different groups of organisms were found in the different regions. b. Even though the limbs of various mammals carry out different functions (swimming, gliding, running, holding, etc.), the bone patterns are very similar. c. Some fossils of extinct organisms are quite different from living organisms. d. The limbs of some mammals serve the same purpose but their bone patterns are very different. e. The platypus is only found in Australia and the dodo was only found on Madagascar.
The left and right hemispheres of the brain are linked by tracts that cross in the area called the
A. thalamus. B. corpus striatum. C. corpus callosum. D. medulla oblongata.