1. CELL HOMEOSTASIS & TRANSPORT

2. Cell Transport  Cell transport is moving materials into, out of, or within the cell  Transport within the cell (intracellular) is accomplished by the endoplasmic reticulum (ER) and cytoplasmic streaming  Transport between cells is accomplished through the plasma membrane  Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells  Recall: what is homeostasis?

3.  Purpose of cell transport:  Cells need to bring in materials necessary for homeostasis  Cells need to get rid of wastes  Cells produce materials that will be used in other parts of the cell, or outside the cell in other parts of the organism  Types of cell transport:  Passive transport  Active transport

4. Passive Transport  Passive transport: crossing of substances through the cell membrane without any input of energy by the cell  Types of passive transport:  Diffusion  Osmosis  Facilitated diffusion

5. Diffusion  Simplest type of passive transport  Diffusion: the movement of molecules from an area of higher concentration to an area of lower concentration  Driven by the molecules’ kinetic energy  In the absence of other influences, diffusion will eventually cause the molecules to be in equilibrium  Diffusion across a cell membrane is also called simple diffusion Allows certain molecules to pass through the membrane Depends on the size and type of molecule and on the chemical nature of the membrane

6. Osmosis  Osmosis: the process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration  Water passes freely through the cell membrane  Water content is determined by the concentration of water inside and outside the cell  Water will move from where there is more of it to where there is less of it

7.  Direction of osmosis depends on the concentration of solutes on the two sides of the membrane  When concentration of solute molecules outside the cell is lower than the concentration in the cytosol, the outside is hypotonic  Water will diffuse into the cell  When concentration of solute molecules outside the cell is higher than the concentration in the cytosol, the outside is hypertonic  Water will diffuse out of the cell  When concentrations of solutes outside and inside the cell are equal, the outside is isotonic  Water diffuses inside and outside the cell at equal rates

8. Facilitated diffusion  Facilitated diffusion: type of passive transport used for molecules that cannot readily diffuse through cell membranes  Movement of these types of molecules across the cell membrane is assisted by specific proteins in the membrane Ion Channels  Another type of transport involves membrane proteins known as ion channels  Transport ions such as sodium (Na + ), potassium (K + ), calcium (Ca 2+ ), and chloride (Cl - )  Provide small passageways across the cell membrane through which ions can diffuse

9. Active Transport  Active transport: movement of materials from an area of lower concentration to an area of higher concentration with the use of energy from the cell  Types of active transport:  Cell membrane pumps  Endocytosis  Exocytosis

10. Cell Membrane Pumps  Carrier proteins that serve in active transport are often called cell membrane “pumps”  Molecule binds to a specific kind of carrier protein on one side of the cell membrane  protein changes shape  protein transports the molecules through the membrane and releases it to the other side  Ex: Sodium-potassium pump

11. Endocytosis  Endocytosis: the process by which cells ingest external fluid, macromolecules, and large particles, including other cells  Pouch pinches off from the cell membrane and becomes a membrane-bound organelle called a vesicle  Two types of endocytosis: Pinocytosis: transport of solutes of fluids Phagocytosis: movement of large particles or whole cells called phagocytes

12. Exocytosis  Exocytosis: the process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface then fuses with the membrane to be the substance out of the cell  Basically reverse of endocytosis  Cells may use exocytosis to release large molecules such as proteins, waste products, or toxins that would damage the cell if released in within the cytosol

14. Membrane Transport Animation