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Transcript
Passive Transport (Chapter 7.4) Passive transport movement across the cell membrane that does not require energy from the cell. Brownian Motion random motion of atoms and molecules. solids, liquids, and gases. Diffusion the net movement of particles from an area of higher concentration to an area of lower concentration (perfume or food coloring and water) results because of Brownian motion. 3 Key Factors that affect Diffusion 1. Concentration: the more concentrated the more rapidly diffusion will occur (collisions with more particles). 2. Temperature: Increased temp. =increased energy = more rapid particle motion à increases rate of diffusion 3. Pressure: Increased pressure = increased particle motion = increased rate of diffusion Equilibrium when the concentration of a substance is equal throughout a space. materials moving out of the cell equals the materials moving into the cell. Concentration Gradient a difference in the concentration of a substance across a space food coloring example Ions and molecules move with the gradient. Why? Because they move from higher concentration to lower concentration (diffusion) **If there are no interruptions, diffusion will continue until there is no longer a concentration gradient At this point dynamic equilibrium occurs Note: Diffusion doesn’t have to only take place using substances in aqueous environment. Example: Oxygen (gas) diffuses into capillaries because oxygen concentration is higher in lung air sacs then the concentration in the capillaries 1 Osmosis diffusion of water across a selectively permeable membrane What controls Osmosis? concentration gradient Osmosis affects cells most cells surrounded by water 3 types of solutions 1. hypertonic solution a. water moves out of the cell b. causes the cell to shrink c. animal cell shrivels and wilting plants outside the cell Dissolved particles Water molecules 2. hypotonic solution a. water moves into the cell b. causes cell to swell c. could cause animal cells to burst and plant cells to become plump. (plant cells won't burst because the cell wall protects it) outside the cell Dissolved particles Water molecules 3. inside the cell Dissolved particles Water molecules inside the cell Dissolved particles Water molecules Isotonic Solution a. No net water movement. b. Water diffuses into and out of the cell at equal rates c. Cell stays the same size d. Dissolved particles and water molecules are = in and out of the cell 2 Crossing the Cell Membrane Reminder: transport proteins (channel) Ions like Na, K, Ca, and Cl can not pass through the nonpolar inner part of the membrane because they are polar but they can diffuse through ion channels. ion channels a transport protein with a polar pore through which ions can pass. Facilitated Diffusion Carrier proteins transport substances down their concentration gradient through a process called Facilitated diffusion type of passive transport that does not require any energy. 3