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mkwilliams mkwilliams
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Posts: 483
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6 years ago
Explain the processes of phloem loading and unloading in a flowering plant
 
  What will be an ideal response?

Question 2

Explain the process that occurs when a stoma goes from closed to open.
 
  What will be an ideal response?
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Replies
wrote...
6 years ago
Answer to q. 1

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.

Answer to q. 2

When triggered by items such as blue light or a decrease in carbon dioxide concentration, guard cells
will undergo activity changes that will change them from flaccid to turgid. Turgid guard cells bend
away from each other, opening the space between them (the stoma). The process that leads guard cells
to become turgid is as follows. First, protons are pumped out of the guard cells by active transport.
Then, protons flow back into the cells, providing energy for active transport of K+ into the cells. This
increases the solute concentration inside the cells, so water then follows into the cells by osmosis. The
movement of water into the cells causes turgor pressure to build until the guard cells become turgid,
thus opening the stoma.
mkwilliams Author
wrote...
6 years ago
Smiling Face with Open Mouth that's the expression my face made when I got the notification email
wrote...
6 years ago
glad I put that smile on your face Happy Dummy
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