Homeostasis and Transport

1. Homeostasis and Transport

2. Homeostasis and Transport • Homeostasis: the biological balance between a cell or an organism and its environment • A cell needs to ….. • Maintain water balance • Take in and export molecules • Take in food • Get rid of waste • Release heat energy

3. Homeostasis and transport These things are done through the cell membrane by the following processes: Active Transport: requires energy use by the cell Exocytosis Endocytosis Cell membrane pumps • Passive transport: does not require energy use by the cell • Diffusion • Osmosis • Ion channels • Facilitated diffusion

4. Passive Transport: Diffusion • Diffusion: the process by which molecules move from an area of high concentration to areas of lower concentration. • Diffusion occurs to all molecules regardless of physical state or size. • Molecules move along a concentration gradient (the difference of concentration of molecules along a space) • Over time the concentration of the molecules in that space will become evenly distributed = equilibrium

5. Passive Transport: Osmosis • Osmosis:special case of diffusion where H2O molecules diffuse across a selectively permeable membrane.

6. Tonicity • Hypotonic: concentration of water molecules outside of the cell is higher than inside the cell. (or concentration of solute molecules is lower outside the cell than inside) • Hypertonic: concentration of water molecules outside of the cell is lower than inside the cell. (or concentration of solute molecules is higher outside the cell than inside) • Isotonic: the concentrations of water and solute are equal inside the cell and outside the cell

7. Osmosis • Osmosis and cells: • The cells of most organisms usually exist in a isotonic environment, so water balance is not a problem • But…… • Freshwater protistslive in a hypotonic environment so must have an adaptation to cope with the influx of water • Contractile vacuole: special “pump” in protist that removes excess water. Uses energy

8. Osmosis • Plant cells are mostly in a hypotonic environment. • The cells swell with water until the cell membrane puts pressure on the cell wall, which can take the pressure • Turgor pressure • When water is scarce the plant cells shrink and the cell membrane tears away from the cell wall • Plasmolysis

9. Osmosis • Cells such as blood cells have no means to deal with swelling or shrinking due to changes in the environment. They will either shrivel up with to little water, or burst from too much water (cytolysis)

10. Facilitated Diffusion • Facilitated Diffusion: molecules that cannot easily pass through the cell membrane may be assisted by carrier proteins built into the membrane • Molecules can move down a concentration gradient through the channels, so the cell doesn’t spend any energy • Ex. Glucose—too large to fit through the membrane quickly enough to satisfy energy needs of cells. • Special channels just for simple sugarsspeed up the diffusion process.

11. Ion Channels • Special membrane proteins made for ions such as Na+, K+and Cl- • Usually specific channels for each ion • Some channels always open, others are “gated” and open in response to stimuli

12. Active Transport • Movement of materials across the cell membrane from areas of LOWER concentration to areas of HIGHER concentration—against the concentration gradient • Made possible by carrier proteins • Ex. Sodium potassium pump

13. Sodium Potassium pump • Sodium-potassium pump: works to increase the [Na+] outside the cell and increase the [K+] inside the cell. • Steps: • 3 Na+from cytoplasm attach to carrier protein • ATP gives up a phosphate to the protein causing a shape change that allows the Na+ to be released to the outside (energy given by ATP) • 2 K+bind to the carrier protein, which then releases the Phosphate and shape change allows K+to enter the cell

14. Sodium potassium pump • Difference in charges on the inside and outside of cell create an electrical current that can travel from cell to cell—used by nerve cells to conduct impulses • Many other types of pumps exist to move molecules against the concentration gradient

15. Sodium potassium pump

16. Other forms of Active Transport • Endocytosis and exocytosis • endocytosis: ingestion of larger particles and fluids by the cell. Materials brought in are contained within a membrane-bound structure called a vesicle. • Pinocytosis: ingestion of fluids or solutes • Phagocytosis: ingestion of large particles or whole cells • Unicellulars consume food • Animals consume bacteria and viruses (phagocytes or killer T cells) • Fuse with lysosomes for digestion

17. Other forms of Active Transport • Exocytosis: export of materials contained in vesicles by the cell • May release product produced in the cell then packaged by the golgiapparatus • Used by endocrine system to release hormones