PLANT PHYSIOLOGY
TRANSPORT IN PLANT
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Root pressure
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The osmotic uptake of water by sieve tubes at the sink
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The osmotic uptake of water by sieve tubes at the source
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The accumulation of mineral and water by the stele in the root
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Detailed explanation-1: -Cells in a sugar source “load” a sieve-tube element by actively transporting solute molecules into it. This causes water to move into the sieve-tube element by osmosis, creating pressure that pushes the sap down the tube.
Detailed explanation-2: -The Pressure-Flow Hypothesis The pressure is created by the difference in water concentration of the solution in the phloem and the relatively pure water in the nearby xylem ducts. At their “source”-the leaves-sugars are pumped by active transport into the companion cells and sieve elements of the phloem.
Detailed explanation-3: -The sucrose diffuses through the plasmodesmata from the companion cells to the sieve tube elements. As a result, concentration of sucrose increases in the sieve tube elements. Water moves by osmosis from the nearby xylem in the same leaf vein. This increases the hydrostatic pressure of the sieve tube elements.
Detailed explanation-4: -Due to concentration of sugars like sucrose in phloem, it increases the osmotic pressure in the cells of phloem. This makes water to move into phloem cells through osmosis.
Detailed explanation-5: -According to the pressure flow hypothesis, food is prepared in the plant leaves in the form of glucose. Before moving into the source cells present in the phloem, the prepared food is converted into sucrose.