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Transcript
Chapter 4 – Cells and their Environment Mr. Lopez – Ag. Biology – Shandon High School California Content Standards: 1a, 1b, 10b, 10d, IE1d Section 1 - Passive Transport • Homeostasis maintained by controlling the movement of substances across the cell membrane • Movement of substances can be accomplished in two ways: passive or actively. Section 1 - Passive Transport (continued) What is passive transport? • Movement across the cell membrane that does not require energy • Figure 1 on page 75 provides an example of passive transport. Section 1 - Passive Transport (continued) Section 1 - Passive Transport (continued) Difference in concentration of substances is known as? • Concentration gradient When the concentration of a substance is equally distributed, it is know as? • Equilibrium Section 1 - Passive Transport (continued) What is diffusion? • The movement of a substance from an area of high concentration to an area of lower concentration due to random motion Section 1 - Passive Transport (continued) • Molecules and ions enter and leave the cell by diffusion • Many times the concentrations of substances very between the cell and the outside • Yet remember that the membrane is “selectively permeable” – Nonpolar lipid layer repel ions and most polar molecules Section 1 - Passive Transport (continued) • Osmosis – Diffusion of water through a selectively permeable membrane – Figure 2, shows how osmosis occurs across the membrane. Section 1 - Passive Transport (continued) • Hypertonic Solution – As water diffuses out of a cell, the cell shrinks – Fluid outside the cell has a higher concentration of dissolved particles • Hypotonic Solution – As water diffuses into a cell, the cell swells – Fluid outside the cell has a lower concentration of dissolved particles Section 1 - Passive Transport (continued) • Isotonic Solution – No changes in size – State of equilibrium is reached – Water diffuses in and out at the same rate Section 1 - Passive Transport (continued) • Crossing the Cell Membrane – Ions and polar molecules are able to enter cells via the aide of transport proteins – Transport proteins known as channels provide polar passageways that allow specific substances to pass through the cell – For example, ions like sodium, Na+, potassium, K+, calcium Ca2+, chloride, Cl-, cross into the cell via ion channels Section 1 - Passive Transport (continued) Section 1 - Passive Transport (continued) – Movement of charged particles also influenced by the particle’s positive or negative electrical charge – In general, the inside of cells are negatively charged – Therefore positively charged ions are more likely to enter the cell – Negatively charged ions are more likely to leave the cell Section 1 - Passive Transport (continued) • What are carrier proteins? – Binds to specific substances in membrane – Carry the substance across the membrane – Release the substance where it is needed by concentration gradient – This “ride-along” of the substance is known as facilitated diffusion Section 1 - Passive Transport (continued)