Cellular Transport

1. Cellular Transport Section 8.1 p. 195 - 200

3. 8.1 Osmosis worksheet

4. Osmosis: Diffusion of Water • The plasma membrane controls what can enter or leave a cell. • The plasma membrane does not limit the amount of water that passes or diffuses through. • Remember… diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

5. Osmosis: Diffusion of Water • In cells, the water wants to have equal concentrations of substances on both sides of the membrane. • The diffusion of water across a selectively permeable membrane is called osmosis. • Regulating water flow through the plasma membrane is important to maintaining homeostasis.

6. What controls osmosis? • If a strong solution and a weak solution of the same things are put in direct contact, the water molecules will diffuse in one direction. • The water will go toward the stronger side until the concentration is the same everywhere. • The water wants to go to the area of higher concentration (the stronger solution)

7. Selective permeability = like a screen Some things can come in and some things are kept out

8. 24 sugar molecules on this side 24 sugar molecules on this side 6 sugar molecules on this side 6 sugar molecules on this side During osmosis, water diffuses across a selectively permeable membrane. Notice that the number of sugar molecules did not change on each side of the membrane, but the number of water molecules on either side of the membrane did change.

9. Cells in an isotonic solution • Same concentration on both sides • Diffuses in and out at the same rate • Cells retain their normal shape

10. Cells in an isotonic solution – neutral …same concentration on both sides In an isotonic solution, water molecules move into and out of the cell at the same rate, and the cells retain their normal shape as in (A). Notice the concave (normal) disc shape of a red blood cell in (B). A plant cell has its normal shape and pressure in an isotonic solution in (C).

11. Put the fish in an isotonic solution It would be like putting a freshwater fish in a freshwater fish tank…

12. Put the fish in an isotonic solution The fish would stay the same size.

13. Cells in a hypotonic solution • Concentration of dissolved substance is lower in the solution outside the cell • There is more water outside the cell • Cells in hypotonic solutions experience osmosis that FLOWS IN • The cell swell and internal pressure increases

14. Cells in an hypotonic solution – concentration of dissolved molecule lower outside the cell In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell (A). Animal cells, like these red blood cells, may continue to swell until they burst. (B). Plant cells swell beyond their normal size as pressure increases (C).

15. Put the fish in an hypotonic solution It would be like putting a saltwater fish in a freshwater fish tank…

16. Put the fish in an hypotonic solution The fish would swell… it may even burst!

17. Cells in a hypertonic solution • The concentration of dissolved substances is higher outside the cell than inside the cell • Cells in hypertonic solutions experience osmosis that causes water to FLOW OUT • Animal cells shrink in hypertonic solutions because of decreased pressure • Plants wilt under these conditions

18. Cells in an hypertonic solution – concentration of dissolved molecule higher outside the cell In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink (A). Animal cells like these red blood cells shrivel up as they lose water (B). Plant cells lose pressure as the plasma membrane shrinks away from the cell wall (C).

19. Put the fish in an hypertonic solution It would be like putting a freshwater fish in a saltwater fish tank…

20. Put the fish in an hypertonic solution The fish would shrivel like a raisin.

21. Salt sucks… if you are a slug… is the a hyper or hypotonic environment for the slug? Remember…Higher concentration on the outside = ?

24. 8.1 Transport worksheet

25. Concentration gradient • This diagram shows a “concentration gradient”. • There is a higher concentrate of dissolved particles on one side.

26. Concentration gradient • When we move from areas of higher concentration to lower concentration, we are moving with the gradient. • When we move from areas of lower concentration to higher concentration, we are moving against the gradient.

27. Passive transport • With the concentration gradient – from higher concentration to lower concentration • Requires no energy

28. Passive transport by proteins • Transport proteins in plasma membrane help or “facilitate” movement of substances through the membrane • This movement is with the concentration gradient • It requires no energy

29. Passive Transport Passive transport can occur by (A) simple diffusion, (B) facilitated diffusion by channel proteins, and (C) facilitated diffusion by carrier proteins.

30. Active Transport • Cells can move substances from areas of lower concentration to areas of higher concentration • This is moving against the concentration gradient • This will require extra help from carrier proteins • Energy is needed!

31. How active transport occurs • A particle binds with a carrier protein – usually pretty specific (like a lock and key) • When the correct ones fit, chemical energy allows the cell to change the shape of the carrier protein like opening a door. • Once the particle is on the other side, the carrier protein goes back to its normal shape.

32. Carrier proteins are used in active transport to pick up ions or molecules from near the cell membrane, carry them across the membrane, and release them on the other side. Why does active transport require energy? Molecules tend to move from higher to lower concentration. Active transport reverses the trend requiring energy input.

33. Transport Through the Plasma Membrane

34. Transport of large particles • Endocytosis = cells surrounds and takes in materials from its environment. • The material does not just pass through the plasma membrane but instead is engulfed and covered by a bubble of membrane that moves inside the cell. • Some single cell organisms like amoebas eat this way. • This does require energy.

35. Transport of large particles • Exocytosis = the opposite of endocytosis. • The expulsion of waste materials from the cell.

36. Some unicellular organisms ingest food by endocytosis and release waste or cell products from a vacuole by exocytosis.