PLANT PHYSIOLOGY
TRANSPORT IN PLANT
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Phloem sap is able to flow in sieve elements against the pull of gravity
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Sucrose is loaded into sieve elements against a conc. gradient
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Sucrose passes out of the phloem into regions where cells are dividing
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water follows sucrose into a sieve element down a water potential gradient
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Detailed explanation-1: -Water follows the sugar molecules into the sieve elements through osmosis (since water passively diffuses into regions of higher solute concentration). This water creates turgor pressure in the sieve elements, which forces the sugars and fluids down the phloem tubes toward the sinks.
Detailed explanation-2: -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.
Detailed explanation-3: -It allows for efficient energy transfer and increased energy storage (sucrose is a disaccharide and therefore contains more energy)
Detailed explanation-4: -Phloem transport is called active because phloem loading at the source and unloading at the sink are both done by active transport. This is a biological process in which molecules move against a concentration gradient, requiring chemical energy to transport biochemical substances from a lower to a higher concentration.