9700 · 7.2
Transport mechanisms flashcards
Revision flashcards for Cambridge 9700 Transport mechanisms (syllabus 7.2). Flip, recall, then mark a real past-paper question.
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Define simple diffusion.
Net movement of molecules down a concentration gradient across the membrane without proteins or ATP.
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Define facilitated diffusion.
Passive transport of polar molecules/ions through channel or carrier proteins down a concentration gradient.
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Define osmosis.
Net movement of water from higher to lower water potential across a partially permeable membrane.
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Water potential equation?
$\Psi = \Psi_s + \Psi_p$ (solute potential plus pressure potential).
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Apoplastic pathway?
Water movement through cell walls and intercellular spaces; blocked at Casparian strip in endodermis.
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Symplastic pathway?
Water movement through cytoplasm and plasmodesmata, crossing membranes at each cell.
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What is translocation?
Mass flow of assimilates in phloem from photosynthetic source to metabolic sink.
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Cohesion-tension theory?
Transpiration pull + hydrogen-bond cohesion + adhesion moves water up xylem as a continuous column.