PLANT PHYSIOLOGY
TRANSPORT IN PLANT
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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the phloem has a negative pressure since its cells are dead
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the phloem has a higher solute concentration
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the xylem has a higher pressure since there is more water in the xylem
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None of the above
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Detailed explanation-1: -The increased solute concentration causes water to move by osmosis from the xylem into the phloem. The positive pressure that is produced pushes water and solutes down the pressure gradient. So, the correct answer is “Osmosis".
Detailed explanation-2: -The presence of high concentrations of sugar in the sieve tube elements drastically reduces s, which causes water to move by osmosis from xylem into the phloem cells.
Detailed explanation-3: -At their “source”-the leaves-sugars are pumped by active transport into the companion cells and sieve elements of the phloem. As sugars (and other products of photosynthesis) accumulate in the phloem, water enters by osmosis.
Detailed explanation-4: -Plants lose water (and turgor pressure) via transpiration through the stomata in the leaves and replenish it via positive pressure in the roots. Pressure potential is controlled by solute potential (when solute potential decreases, pressure potential increases) and the opening and closing of stomata.
Detailed explanation-5: -It states that mass flow of solutes takes place in the phloem in the following stages: Sucrose moves from companion cells into sieve tube elements by active transport. This reduces the water potential of the sieve tube element. Water moves into the phloem by osmosis, which increases the hydrostatic pressure.