Cell Transport

1. Cell Transport Getting things in and out of cells

2. 1 Why do we need cell transport? • Cells live in a liquid environment. • The membrane keeps the cell’s internal conditions relatively constant by moving in things that are needed and moving out things that are waste or that need to go somewhere else to help other cells.

3. 2 Is energy involved? • Two basic types of cell transport: • Passive – no energy needed because it goes with the concentration gradient Ex. Diffusion, Facilitated Diffusion, and Osmosis • Active – requires energy because it goes against the concentration gradient Ex. Protein pumps, endocytosis, exocytosis

4. 3 concentration gradient • The natural tendency of molecules dissolved in a liquid environment to move from an area of higher concentration to an area of lower concentration. • In solution, molecules are constantly moving. • When this occurs across a cell membrane, we call it diffusion.

5. 4 Diffusion • Substances will move across the cell membrane from areas of high concentration to areas of low concentration until the concentration is equal on both sides. • When the concentration is equal on both sides, equilibrium has been reached. • Even after equilibrium, particles are still moving back and forth across the membrane, but the net change in concentration is zero. • It relies on the idea that particles are always moving, so no energy is needed. • Particles are usually small and uncharged.

7. 5 Facilitated Diffusion • When molecules that cannot directly diffuse across the membrane because they are too large or have a charge are able to pass through protein channels. • There are hundreds of different proteins, and some are specific and some are nonspecific.

8. 6 Osmosis • Diffusion of water through a selectively permeable membrane. • Because a portion of the cell membrane is hydrophobic, simple diffusion of water is difficult and not as efficient. • So it moves through a protein channel called an aquaporin.

10. osmosis

11. 7 Sugar Solution • Isotonic – equal amount of solute on both sides, so water also moves equally • Hypertonic – the side with a higher concentration of solute • Hypotonic – the side with lower concentration • Water moves until the solute is equal.

12. 8 Osmotic Pressure • The net movement of water out of or into cell produces a force known as osmotic pressure. • Cells in hypertonic shrink (H2O moves out to make solute concentration equal) because concentration of solute is greater outside the cell. • Cells in hypotonic swell (H2O moves in to make solute concentration equal) because solute concentration is greater inside the cell. • In fresh water, most cells would burst.

14. 9 Active Transport • Occurs when materials need to be moved against the concentration gradient, from low to high. • Requires energy • One type are protein (ion) pumps that use energy to bring in molecules such as calcium, potassium and sodium ions. • ATP loses a phosphate bond, which releases energy for this to happen (ATP = ADP + P + energy).

17. 10 Large Molecules and Clumps • Bulk transport is when things are engulfed or internal vesicles are released. • Endocytosis – when materials are brought INTO the cell (engulfed) when the cell membrane folds in or creates a pocket, surrounding the material. phagocytosis – solid material brought in pinocytosis – liquid material brought in

19. 11 Exocytosis • When large amounts of material are released OUT OF a cell. • Vesicle fuses with cell membrane, forcing the contents out. • Contractile vacuoles in parameciums use this exocytosis to remove water.