22 lines
1.4 KiB
Markdown
22 lines
1.4 KiB
Markdown
[[Cell Structure and Function]]
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Type of passive diffusion that allows molecules that can't cross the hydrophobic core on their own using channel or transport proteins. Requires no energy.
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# Summary
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* Aquaporins are channel proteins that move large quantities of water across the membrane.
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* Facilitated diffusion uses transport and channel proteins to move molecules that can't cross the hydrophobic core on their own across the membrane. (More info in Membrane Transport)
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* Movement of ions across membrane can polarize it, creating an uneven charge distribution
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**How molecular structure decides the route:**
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- Small and nonpolar: passes directly through the bilayer.
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- Large and polar (like glucose): needs a transport protein.
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- Charged ion (like Na⁺ or K⁺): needs a channel protein.
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Water can cross the membrane on their own but it's slow, aquaporins transport large quantities.
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| Transport Type | Energy Required? | Direction | Examples |
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| --------------------- | ---------------- | ----------- | --------------------------------------- |
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| Simple Diffusion | No | High to Low | O₂, CO₂ |
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| Facilitated Diffusion | No | High to Low | Glucose, ions, water through aquaporins |
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| Active Transport | Yes (ATP) | Low to High | Na⁺/K⁺ pump, calcium pumps |
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Key difference between simple and facilitated is the protein. |