1. HOMEOSTASIS AND CELL TRANSPORT
Chapter 5
Biology I

2. Vocabulary- Chapter 5 (23 words)
Passive transport facilitated diffusion Diffusion carrier protein Concentration gradient ion channels Equilibrium phagocyte Osmosis exocytosis Hypotonic pinocytosis Hypertonic phagocytosis Isotonic endocytosis Contractile vacuole vesicle Turgor pressure active transport Plasmolysis sodium-potassium pump cytolysis

3. Passive Transport
*Cell membranes help organisms maintain homeostasis by controlling what substances enter or leave the cell
*passive transport: substances pass across the cell membrane without any input of energy by the cell
Diffusion: the movement of molecules from an area of higher concentration to an area of lower concentration
Concentration gradient: the difference in the concentration of molecules across a distance

4. Passive transport driven entirely by the molecule’s kinetic energy- molecules in constant motion
Equilibrium: the concentration of molecules will be the same throughout the space the molecules occupy
Even at equilibrium, there is still balanced movement
Some membranes allow molecules to pass through, but not others- if allowed, it will diffuse
Examples: carbon dioxide and oxygen diffuse across membranes

5. hypotonic: solutes lower outside, water moves in
Osmosis- water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration
Passive transport of water
Direction of Osmosis…
…depends on the concentration of solutes on both sides of the membrane
hypotonic: solutes lower outside, water moves in
hypertonic: solutes higher outside, water moves out
isotonic: solutes equal on both sides, water moves equally in and out
THE NEXT SLIDE ILLUSTRATES THIS…

7. How cells deal with osmosis
Contractile vacuoles: organelles that remove water
Occurs in organisms that live in hypotonic solutions (example: paramecia)
Requires the use of energy

8. Some cells pump solutes out, changing the flow of water
Animal cells and most plant cells live in hypotonic solutions
Tugor pressure: the pressure water exerts against the cell wall- occurs in a hypotonic solution
Plasmolysis: the cell shrinks away from the cell wall in a hypertonic solution (example: plants wilting)

10. Some cells can’t compensate for changes in the solute concentration of their environment (example: red blood cells will eventually burst)
Cytolysis: the bursting of cells

12. A type of passive transport… Facilitated diffusion- the transport of substances through a cell membrane along a concentration gradient with the aid of carrier proteins
Example: glucose- molecule too big to cross freely

13. Diffusion through ion channels
Ion channels: a complex of protein molecules in a cell membrane that form a pore through which ions can pass Examples: sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-)

14. Active Transport- the movement of chemical substances, usually across the cell membrane, against a concentration gradient; requires cells to use energy
Cell membrane pumps Sodium-potassium pump: a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

16. Movement in Vesicles (used when molecules are too large or needed in large quantities)
Endocytosis: the process by which cells ingest external fluid, macromolecules, and large particles, including other cells
vesicle: a small cavity or sac that contains materials in a eukaryotic cell

17. pinocytosis: a type of endocytosis that involves the transport of solutes or fluids
phagocytosis: a type of endocytosis that involves the movement of large particles or whole cells Many unicellular organisms feed this way Phagocytes: a cell that ingests and destroys foreign matter or microorganisms

18. Exocytosis: the process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface and then fuses with membrane to let the substance out of the cell
Cells use exocytosis to release large molecules, wastes, or toxins