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Concentration gradient
differences in the number of molecules or ions of a substance between neighboring region
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Diffusion
- -the net movement of susstances down a concentration gradient
- -passive transport-does not need energy
- -each solute moves down its own gradient
- -Individual modlecules move around whether or not there is a gradient- Brownian movement
- -moves through semipermeable membrane
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Osmosis
- -water crosses membranes- diffusion of water across a plasma membrane
- -three types of condition: hypotonic (more water), hypertonic (less water), isotonic (same amount of water and sucrose)
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Hypotonic conditions
water diffuses in; the cells swell up
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Hypertonic condition
water diffuses out; the cells shrink
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Isontonic condition
no net change in water movement or cell shape
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Plasma Membrane
- -selective permeability
- -small, nonpolar substances slip across
- ( oxygen and carbon dioxide)
- -water (polar) slowly slips through gaps
- -use of transport proteins for: ions, large polar molecule, e.g., glucose (they cannot pass through on their own)
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other mechanisms that substances also cross cell membrane
- 1. facilitated diffusion (passive transport, no ATP, transport proteins)
- 2. active transport (ATP, membrane pumps)
- 3. exocytosis, and
- 4. endocytosis
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endocytosis
a vescile brings substances in bulk into the cell
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exocytosis
a vesicle ejects substances in bulk from the cell, the cell expelled
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metabolism
- most chemical reactions in cell, maintain homeostasis
- -some reaction release energy
- -some reaction require energy
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ATP/ADP cycle
- cells use ATP constantly
- ATP must be replenished
- phosphate bonds store energy
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