1. Homeostasis 7-3 Biology Corsicana High School

2. Homeostasis a biological balance that cells maintain with their environment by controlling what gets into and out of the cell “homeo” = same “stasis” = staying

3. Diffusion the process by which molecules spread from an area of greater concentration to an area of lesser concentration

4. High concentration Low concentration

5. High concentration Low concentration Concentration gradient

6. High concentration Low concentration Concentration gradient

7. UNTIL: EQUILIBRIUM

8. Concentration Gradient the differences in concentrations of a substance across space Molecules will tend to move down the gradient (from higher to lower concentration)

9. Equilibrium is reached when the concentration of molecules is the same throughout a space “equi” = equal “librium” = balance

10. Movement Across Membranes molecules move across membranes by passing between the molecules of the membrane permeable---if a substance can move through a particular membrane, the membrane is said to be permeable to that substance

11. Permeability Depends On: the size of the molecule the type of molecule the molecular structure of the membrane

12. Selectively Permeable a membrane which allows some substances to pass through but not others The cell membrane is selectively permeable

13. Osmosis the process by which water molecules diffuse through a membrane from an area of higher water concentration to an area of lower water concentration The direction of osmosis depends on the relative concentrations of water and solutes inside and outside the cell

14. Hypotonic Solution concentration of solute molecules is less outside the cell than inside “hypo” = below Water molecules will move into the cell, since the water concentration is greater outside

15. 70% water 30 % solutes 10% solutes 90% water

16. 70% water 30 % solutes 10% solutes 90% water

17. Hypertonic Solution concentration of solute molecules is greater outside the cell than inside “hyper” = over Water molecules will move out of the cell, since the water concentration is less outside

18. 70% water 30 % solutes 50% solutes 50% water

19. 70% water 30 % solutes 50% solutes 50% water

20. Isotonic Solution concentration of solute molecules is equal outside the cell and inside “iso” = same Water molecules will move into and out of the cell at equal rates, maintaining equilibrium.

21. 70% water 30 % solutes 70% water

22. 30 % solutes 70% water

23. The terms hypotonic, hypertonic and isotonic refer to the concentration of solutes, but it is the water that moves.

24. Turgor Pressure the pressure against a plant cell wall due to diffusion of water into the cell

25. Plasmolysis a cell wilts due to loss of water from the cell; therefore, a loss of turgor pressure “plasmo” = cytoplasm “lysis” = splitting

26. Cytolysis a cell swells up and bursts due to too much water moving into the cell “cyto” = cell

27. Contractile Vacuole to prevent cytolysis, freshwater animal cells have a special structure which constantly pumps out excess water that diffuses constantly into the cell

28. Passive Transport no cell energy is used diffusion, osmosis are passive transport

29. Facilitated Diffusion carrier molecules (proteins in membrane) transport solutes through the membrane without using cell energy speeds up rate of diffusion a form of passive transport

30. Gated Channel protein-controlled passage that permits the cell membrane to be permeable as needed a form of passive transport

31. Active Transport movement of a substance across a cell membrane using the cell’s chemical energy goes against the concentration gradient---- from lower to higher concentration

32. Sodium-Potassium Pump chemical mechanism that uses active transport to move Na+ out of the cell and K+ into the cell Both ions move against their concentration gradient 1/3 of the energy expended by an animal at rest goes to the Na-K pump

33. 3% Na+ 2% K+ 1% K+ 5% Na+

34. 3% Na+ 2% K+ 1% K+ 5% Na+ Both require the use of energy because the movement is against the concentration gradient.

35. Endocytosis process by which cells engulf substances too large to pass through the cell membrane forms a pouch (vesicle) that enters the cytoplasm “endo” = inside; “cyto” = cell, “-sis” = process

36. Special Forms of Endocytosis pinocytosis---bringing in fluids “pino” = drinking phagocytosis---bringing in large food particles “phago” = eating

37. Exocytosis passage of large molecules out of the cell “exo” = outside reverse process of endocytosis