Homeostasis and Cell Transport

1. Homeostasis and Cell Transport Chapter 5

2. Homeostasis The steady-state physiological condition of the cell or body.

3. Cellular Transport

4. Passive Transport

5. Diffusion impermeable Semi-permeable The movement of particles from an area of high concentration to an area of low concentration. concentration gradient: formed by the concentration of molecules at various points between the high and low areas. permeable Equilibrium: the concentration of molecules will be the same throughout the space the molecules occupy.

6. Osmosis The movement of water molecules across a selectively permeable membrane. Water moves from a region of high concentration to one of low conc.

7. Hypotonic When the concentration of solute molecules outside the cell is lower than the concentration in the cytosol. Water diffuses into the cell until equilibrium is established.

8. Hypertonic When the concentration of solute molecules outside the cell is higher than the concentration in the cytosol. Water diffuses out of the cell until equilibrium is established.

9. Isotonic When the concentration of solutes outside and inside the cell are equal. Water diffuses into and out of the cell at equal rates, so there is no net movement of water.

10. Contractile Vacuole Organelles in paramecia that collect excess water and then contract, pumping the water out of the cell. Not a form of Passive Transport. Why?

11. Turgor Pressure The pressure that water molecules exert against the cell wall. Plasmolysis: the shrinking of the cell membrane of a plant cell in a hypertonic solution in response to the loss of water by osmosis.

12. Cytolysis The bursting of cells.

13. Facilitated Diffusion The transport of substances through a cell membrane along a concentration gradient with the aid of carrier proteins. Carrier proteins: proteins that transport substances across a membrane.

14. Ion Channels • Transport ions such as: Sodium (Na+) Potassium (K+) Calcium (Ca+) Chloride (Cl-) • Not soluble in lipids • Each type of ion channel is usually specific for one type of ion. • Some ion channels are always open, some have “gates.” • Gates may open or close in response to 3 types of stimuli: streching of the cell membrane, electrical signals, or chemicals in the cytosol or external environment.

15. Active Transport Energy in the form of ATP is used to move substances through the transport proteins. Substances can move across a membrane against concentration gradient. The carrier proteins involved are often called cell membrane “pumps.”

16. Sodium-Potassium Pump • Transports Na+ and K+ ions up the concentration gradient. • At top speed, the pump can transport about 450 Na+ ions and 300 K+ ions per second. • The exchange of 3 Na+ ions for 2 K+ ions creates a positively charged environment outside the cell membrane and negatively charged inside the membrane. • Important for the conduction of electrical impulses along nerve cells.

17. Movement in Vesicles • Endocytosis: process by which cells ingest external fluid, macromolecules, and large particles, including other cells. • External materials are enclosed by a portion of the cell’s membrane, which folds itself and forms a pouch. • The pouch pinches off from the cell membrane and becomes a vesicle. • Some vesicles fuse with lysosomes. • 2 types: • pinocytosis • phagocytosis

18. Pinocytosis • Involves the transport of solutes or fluid.

19. Phagocytosis Movement of large particles or whole cells. Phagocytes: cells in animals that use phagocytosis to ingest bacteria and viruses that invade the body. They fuse with lysosomes and enzymes then destroy the bacteria and viruses before they can harm the animal. leukocytes

20. Exocytosis Process by which a substance is released from the cell through a vesicle that transports the substance to the cell membrane and then fuses with the membrane to let the substance out of the cell. Proteins Waste Toxins