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15 Cards in this Set
- Front
- Back
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Why is glucose converted into sucrose for transport? |
It is less easily metabolized when being transported but it is transported back into glucose or starch when it reaches the cell |
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What is translocation? |
The movement of organic solutes around the plant in the phloem from the source to the sink. It is an active process that requires metabolic energy |
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What are assimilates? |
The products of photosynthesis. Although glucose is made from photosynthesis, it's main assimilate is sucrose |
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What is a source and what is a sink? |
The sources where the carbohydrates are created and loaded into the phloem and the sink is where the assimilates and unloaded to tissue cells |
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What are the main sources of assimilates? |
Green leaves and stems, storage organs e.g tubers and food stores in seeds |
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What are the main sinks in a plant? |
Roots that are growing on actively absorbing minerals, meristem that are actively dividing and any part of the plant that is developing foodstores e.g. Fruits |
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What is the symplast route for translocation? |
Sucrose moves through the cytoplasm of the mesophyll cells and on to the sieve tubes by diffusion through the plasmodesmata |
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What is the apoplast route for translocation? |
Sucrose travels through the cell walls and intercellular spaces to the sieve tube elements by diffusion down a conc. gradient maintained by the removal sucrose into the phloem |
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How is sucrose moved into the cytoplasm of companion cells? |
By active transport, H+ ions are actively pumped out of the cell into the surrounding tissue through a proton pump using ATP and H+ returns to the cell down a conc. gradient via cotransporter protein by facilitated diffusion |
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What are the adaptations of a companion cell that's suits it's role in active transport? |
It has lots of mitochondria for ATP production and it also has many infoldings and their cell membranes to give increased SA for more active transport |
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Once in the phloem how does the sucrose move up and down the plant? |
Water moves into the vessel by osmosis from the xylem down a water potential gradient leading to a buildup of hydrostatic pressure. The water carrying the assimilates moves into the sieve tube elements, reducing the pressure in companion cells and sucrose moves from areas of high pressure to areas of low pressure |
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How is sucrose unloaded to the cells? |
By diffusion down the conc. gradient. It can also be converted into glucose / starch to be diffused. As solutes leave the water potential of the phloem Rises so water moves out of the vessel by osmosis into surrounding cells |
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What are the 4 pieces of evidence that provide evidence for the active processes in translocation? |
Advances in microscopy allow us to see the adaptations of companion cells by active transport such as having many mitochondria
If mitochondria poisoned in a companion cell translocation stops
The flow of sugars in phloem is 10000 times faster than it would be by diffusion alone suggesting an active process is driving mass flow
Aphid studies have shown that there is a positive pressure and therefore flow rate in the phloem close to the source and sap can be forced out through the stylet of the aphid |
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What is a plant that possesses transport tissues called? |
Vascular |
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Why does the trunk swell above a cut when a ring of bark is removed? |
Because sugars can't pass the cut and they stuck above it There is a decrease in the water potential so water moves into cells |
