Homeostasis & Transport

1. Homeostasis & Transport Chapter 5

2. Passive Transport Section 5.1

3. Homeostasis • To remain alive and function optimally, cells must maintain a biological balance with their immediate environment called _______?

4. Homeostasis? • How do cell membranes help maintain homeostasis within a cell? • By controlling what goes into and out of the cell, called semi-permeable.

5. Cell Membrane Permeability • What determines the permeability of a substance across the cell membrane? • Size • Polarity • Hydrophobic vs. hydrophilic • Charge

6. Permeability of Cell Membrane

7. Selectively Permeable • The cell membrane is described as selectively permeable because it allows some substances to pass in or out but not others. • The size, charge, and polarity of a substance determines its permeability. • The cell membrane is permeable to gases such as carbon dioxide and oxygen since gases are small. • The cell membrane is permeable to water and other small, polar molecules.

8. Passive Transport • The movement of substance across a cell membrane WITHOUT the use of energy (ATP). • Four Types: • Diffusion • Osmosis • Facilitated Diffusion • Ion Channels

9. 1. Diffusion • Movement of molecules from an area of high concentration to an area of low concentration without the help of energy.

11. Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW)

12. Concentration Gradient • Difference in concentration of molecules across a space (or cell membrane). • “Down the gradient” Movement from high to low concentration

13. Equilibrium • When the concentration is EQUAL throughout the space (or on each side of the cell membrane) • End of diffusion • RANDOM movement still occurs

14. Diffusion of Liquids

15. Diffusion across a membrane • Depends upon temperature, size, shape, and chemical makeup • Easy to diffuse: • Small (eg. O2 ) • Nonpolar Hard to diffuse: • Glucose • amino acids

16. Diffusion and Equilibrium

17. Main Points • Diffusion – molecules cross the cell membrane without using energy • Always moves from higher concentration to lower concentration • Ability to diffuse depends on size & type of molecule

18. 2. Osmosis • WATER diffusion across a membrane quickly • “higher to lower concentration, DOWN THE GRADIENT • Hypotonic solution to hypertonic solution

19. Hypotonic Solution • The solute concentration is higher inside the cell, the water concentration is higher outside the cell. • Net movement = Water into the cell

20. Hypertonic Solution • The solute concentration is higher outside the cell, the water concentration is higher inside the cell. • Net movement = Water out of the cell

21. Isotonic Solution • The solute and water concentrations are EQUAL on both sides of the membrane. • Equilibrium

23. Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic

24. Cells deal with osmosis • Cells live in isotonic environment – water moves with no problem • Freshwater organisms – freshwater outside (hypotonic environment) of the cell makes too much water go into the cells because of osmosis, cells can burst

25. Facilitated Diffusion • movement of molecules that can’t diffuse by themselves through cell membrane • Use of specific carrier proteins the assist diffusion across a membrane. • (like glucose or amino acids) THIS IS HOW GLUCOSE ENTERS CELL RAPIDLY • “Down the gradient” means high to low concentration

26. Diffusion via ion channels • Use of membrane proteins to assist diffusion of ions across a membrane • Channel is usually specific to 1 type of ion • Some always open, some are “gated” • Common ions: • Sodium • Potassium • Chlorine • Calcium

27. Active Transport Section 5.2

28. Active Transport • Uses energy (ATP) to move materials against the gradient • “Up the gradient” • Low to high concentration

29. 1. Sodium Potassium Pump • Transports sodium and potassium ions across the membrane up their gradients • Complete cycle 3 Na +out & 2 K+ inside cell • Low to high concentration • Uses ATP

30. 2. Endocytosis • Movement of large amounts of material into the cell • Folding cell membrane to form a vesicle that will go to the lysosome for digestion • Uses ATP

31. 2 types of endocytosis • 1. pinocytosis: “cell drinking” • movement of a large quantity of solutes or liquid into the cell • 2. phagocytosis: “cell eating” • Movement of large solids or whole cells into the cell • Uses ATP

32. Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis.

33. 3. Exocytosis • The movement of a large amount of materials out of the cell • removes wastes and cell products like proteins packaged by Golgi vesicles • Vesicle fuses to the cell membrane to release contents out of the cell • Uses ATP

34. Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.

35. Passive & Active Transport • Animation