Chapter 5: Homeostasis & Transport

1. Chapter 5:Homeostasis & Transport

2. DIFFUSION/OSMOSIS: • MOVEMENT OF MATERIALS THROUGH THE CELL MEMBRANE

3. Cell membrane: • helps maintain homeostasis by controlling what enters or leave cells. • Homeostasis (maintaining stability) • It is selectively permeable, only allowing certain molecules to pass through.

4. Passive Transport • Some substances can cross the cell membrane without any input of energy by the cell. • The movement of such substances across the membrane is known as passive transport

5. To stay alive, a cell must exchange materials such as food, water, & wastes w/its env’t. • Small molecules like water can move in and out freely but large molecules cannot.

6. Diffusion • the movement of molecules from an area of higher concentration to an area of lower conc. • HIGHER  lower • Diffusion is a type of passive transport because it does not require energy • The difference in the conc. of molecules across a membrane is called a concentration gradient

8. Increasing rate of diffusion • Concentration • (ammonia) • Pressure • (spray can) • Temperature • (water boiling – molecules move faster)

9. Solutions • Solutions: mixture of 2 or more substances dissolved together. • Example: Salt water • Solute - substance that is dissolved (salt) • Solvent - subst. the solute is dissolved in (water) • Water serves as the main solvent in living things

10. equilibrium • Diffusion continues until conc. is the same on both sides of a membrane • When a conc. gradient no longer exists, equilibrium has been reached BUTmolecules will continue to move equally back & forth across a membrane. • There is always movement back & forth across a membrane.

11. Types of Solutions… • Hypertonic • Hypotonic • Isotonic

12. Hypertonic Solution • Solute conc. outside the cell is higher • (less H2O outside) • H2O diffuses out of the cell until equilibrium is reached • Cells shrink & die if too much H2O is lost • Plant cells become flaccid (wilt); called plasmolysis

13. Hypotonic Solution • Solute conc. inside the cell is higher • (less H2O inside) • H2O moves into the cell until equilibrium is reached

14. Animal cells swell & burst if they take in too much H2O, called Cytolysis • Plant cells become stiff or firm due to H2O pressing against the cell wall. • Turgor pressure in plant cells helps them keep their shape

15. Isotonic Solutions • Conc. of solutes same inside & outside the cell • H2O moves into & out of cell at an equal rate

17. OSMOSIS • Osmosis is the diffusion of H2O. • Diffusion of H2O from an area of higher conc. (less solute) to an area of lower conc. (more solute)

18. How do we deal w/osmosis? • The cells of land animals are usually in isotonic env’t (equilibrium) • Freshwater organisms live in hypotonic env’t so H2O constantly moves into their cells • Unicellular freshwater organisms use energy to pump out excess H2O by contractile vacuoles. • Cell walls prevent plant cells from bursting in hypotonic env’t • Some marine organisms can pump out excess salt

19. Facilitated Diffusion • Involves carrier proteins embedded in a cell’s membrane to help move molecules across a membrane.

20. Active Transport… • Movement of molecules across a cell membr. using energy. • Molecules are transported against their concentration gradient from an area of lower to higher concentration (opposite of diffusion.)

21. Example… • Plants use active transport to help roots absorb nutrients from the soil (plant nutrients are more conc. inside the root than outside)

22. Movement of LARGER molecules • ENDOCYTOSIS – cell takes in large molecules • Cell engulfs molecules too large to pass through the membrane naturally. • Folds or pockets swallow the molecules • PHAGOCYTOSIS: cell takes in lg. solids (food) • PINOSCYTOSIS: “ “ liquids (water) • EXOCYTOSIS – movement of large molecules OUT of the cell.

24. THE END