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)

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 Ca 2+, chloride, Cl -, cross into the cell via ion channels

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)