Explain the processes of phloem loading and unloading in a flowering plant
What will be an ideal response?
At a source, such as a photosynthesizing leaf, an excess of solutes such as sucrose will generally be
available. The phloem is loaded with solutes by active transport mechanisms. Mostly this occurs
through companion cells, which take up solutes by active transport. Solutes then pass into sieve tube
members mainly through plasmodesmata. As the sieve tube members fill with solute, their water
potential is lowered compared to surrounding tissues; thus, water then enters them via osmosis. The
entry of water creates pressure potential, which then pushes solutes and water away from the source by
bulk flow. Pressure gradually decreases away from the source at a sink or sinks, so the bulk flow is
toward the sink or sinks. Sinks include locations such as growing shoot tips or roots. At a sink solutes
are unloaded into nearby cells. This unloading of solutes causes water to flow out by osmosis, further
lowering the pressure potential at the sink.
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If a trait results from the action of several genes, it is called a ________ trait
Fill in the blank(s) with correct word
Apes walk on their feet and knuckles. The apes with opposable thumbs have opposable toes.
Answer the following statement true (T) or false (F)
Which of the following is NOT produced by either the ovaries or testes?
a. testosterone b. estrogen c. progesterone d. follicle-stimulating hormone e. androgens
François Jacob and Jacques Monod discovered ________
A) a mechanism for how proteins regulate gene activity B) the degree of genetic similarity between humans and chimpanzees C) the Hox cluster of homeotic genes D) evolutionary changes in the timing and rate of developmental processes E) the parallel between the order of regulatory genes on a chromosome and the location in the embryo where these genes are expressed