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17 Cards in this Set
- Front
- Back
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What is translocation? |
- The process by which organic molecules and some mineral ions are transported from one part of the plant to another |
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What is phloem? |
- made of sieve tube elements - alive (no nucleus) - few organelles - strands of cytoplasm |
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What are sieve tube elements? |
- long, thin structures end to end |
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What are sieve plates? |
- At the ends of sieve tubes - perforations for strands of cytoplasm to pass |
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What are companion cells? |
- associated with sieve tubes - respire/excrete for them - cytoplasm of sieve tube and companion cells joined through pores in side walls |
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What organic molecules are transported in the phloem? |
- Sucrose - Amino acids |
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What are the inorganic ions transported in the phloem? |
- Potassium - Chloride - Phosphate - Magnesium |
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What is the source of a plant? |
- The area where organic molecules are produced |
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What is the sink of a plant? |
- The area where organic molecules are taken out of the plant |
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What are the three phases of the mass flow theory of translocation? |
- Transfer of sucrose into sieve elements from photosynthesising tissue - Mass flow of sucrose through sieve tube elements - Transfer of sucrose from sieve tubes to storage/sink cells |
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Describe the process of transferring sucrose to sieve elements from photosynthesising tissue. |
- sucrose made from photosynthesis products in cells with chloroplasts (source) - sucrose diffuses down conc. gradient (facilitated diffusion) to companion cells - H+ ions actively transported from companion cells to spaces within cell walls - H+ ions diffuse down conc. gradient into sieve tube - sucrose is co-transported into sieve tubes with H+ ions |
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What is mass flow? |
- Bulk movement of a substance through a given channel/area in a specified time |
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Describe the processes in the mass flow of sucrose through sieve tube elements. |
- sucrose actively transported into sieve tubes=low water potential - xylem=high water potential:water moves from xylem to phloem (osmosis)=hydrostatic pressure - at sink=low sucrose conc.=actively transported into cells from sieve tubes - lowers water potential=water moves into cells via osmosis |
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What is the hydrostatic pressure like in the different regions of the sieve tube during the second stage of translocation? What does this lead to? |
- high hydrostatic pressure in sieve tubes at the source - low hydrostatic pressure in sieve tubes at the sink - mass flow of sucrose down hydrostatic gradient in sieve tubes |
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Describe the process of transfer from sucrose from sieve tubes to storage/sink cells. |
- sucrose actively transported by companion cells out of sieve tubes into sink cells |
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What evidence is there for mass flow theory? |
- pressure in sieve tube=sap released when out - sucrose conc. in source > sink - increase leaf sucrose levels closely followed by increase phloem sucrose - companion cell possess mitochondria/readily produce ATP |
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What evidence is there against mass flow theory? |
- sucrose delivered at same rate to all regions rather than going quicker to regions of lowest sucrose conc. - function of sieve plates unclear=seem to hinder mass flow - not all solutes move at same speed (should if mass flow) |
