Homeostasis and Cell Transport Chapter 5

HSCE: B2.5h Explain the role of cell membrane as a highly selective barrier (diffusion, osmosis, and active transport)

Types of transport systems Passive transport (does not require energy) Active transport (requires energy)

Passive Transport Substances can cross the cell membrane with no energy required. Includes: Diffusion Facilitated (includes Ion Channels) Simple Osmosis

Passive transport Concentration Gradient-the difference in the concentration of molecules across a distance. Substances naturally travel down their concentration gradient (high to low concentration). http://my.hrw.com/sh2/sh07_10/student/fla sh/visual_concepts/60075.htm

Passive transport systems Diffusion-Movement of molecules from an area of higher concentration to an area of lower concentration

Diffusion In the absence of other influences, diffusion will eventually cause the molecules to be in EQUILIBRIUM

Simple Diffusion SIMPLE DIFFUSION- diffusion across a membrane Cell membranes allow certain molecules to pass through, but not others. Depends on the size and type of molecule. Cell membrane

Facilitated Diffusion Some molecules are too large or are not soluble in lipids (can’t pass the lipid bilayer). They need the help of CARRIER PROTEINS. Does not require any extra energy to transport the molecules because they are still traveling from higher to lower concentration (passive transport). molecule Cell membrane (lipid bilayer) carrier protein

Passive Transport Systems Facilitated Diffusion

Facilitated Ion Channels Another type of passive transport carries ions across the membrane through proteins called ION CHANNELS. Ions: sodium (Na+), potassium (K+), calcium (Ca2+), chlorine (Cl-) Each type of ion channel is usually specific to a certain ion. Some channels are always open, others have “gates”. IONS Ion channel

Passive transport systems Osmosis-Movement of WATER molecules across a cell membrane from an area of higher concentration to an area of low concentration. Osmosis

Osmosis Passive transport In a solution, a solute (the substance being dissolved) is dissolved in a solvent (substance doing the dissolving). Example: SUGAR (solute) dissolves in WATER (solvent) In cells the solutes are organic molecules and the solvent is water. OSMOSIS: the process by which water molecules diffuse across a cell membrane from an area of higher to lower concentration.

Direction of Water movement across the membrane Osmosis solute Water molecules Direction of Water movement across the membrane

NO NET MOVEMENT OF H2O (equal amounts entering & leaving) The Plasma Membrane 11/24/2018 Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) PLASMOLYSIS Cells shrink away from cell wall, turgor pressure lost CYTOLYSIS Cell can burst G. Podgorski, Biol. 1010

Hyper-, hypo-, & Isotonic The pressure exerted by water inside the cell wall is called TURGOR PRESSURE When turgor pressure is gained and the cell bursts: CYTOLYSIS When turgor pressure is lost the cell shrinks away from the cell wall and the plant wilts: PLASMOLYSIS Plasmolysis External solution is hypotonic to cytosol: water moves in…cell can burst External solution is isotonic to cytosol: No net movement External solution is hypertonic to cytosol: water moves out…cell shrinks

Osmosis in Red Blood Cells The Plasma Membrane 11/24/2018 Osmosis in Red Blood Cells Isotonic Hypertonic Hypotonic G. Podgorski, Biol. 1010

Cell in Hypotonic Solution The Plasma Membrane 11/24/2018 Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? G. Podgorski, Biol. 1010

Cell in Hypertonic Solution The Plasma Membrane 11/24/2018 Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? G. Podgorski, Biol. 1010

Cell in Isotonic Solution The Plasma Membrane 11/24/2018 Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL NO NET MOVEMENT 10% NaCL 90% H2O What is the direction of water movement? equilibrium The cell is at _______________. G. Podgorski, Biol. 1010

Active Transport systems Active transport moves substances against the concentration gradient (from lower concentration to higher). This requires energy most often supplied by ATP Pumps Sodium-potassium pump Movement in vesicles Move macromolecules and nutrients that are too large to pass the cell membrane or “packs” of small molecules at the same time. Two types Endocytosis Exocytosis

Sodium-Potassium Pump Step 1-3: 3 Na+ bind to protein from inside the cell, a phosphate is removed from ATP binding to the carrier protein and turning ATP into ADP. The protein changes shape releasing the 3 Na+ to the outside. Steps 4-6: The protein then picks up 2 K+ from the inside, the phosphate is removed, changing the shape so that it releases the 2 K+ into the cell.

Sodium Potassium Pump sodium potassium pump

Sodium-potassium pump Pumps 3 Sodium ions out of the cell Pumps 2 Potassium ions into the cell This difference in charge is important for the conduction of electrical impulses along nerve cells.

Endocytosis Cells ingest (take in) external fluid, macromolecules, and large particles. External materials are enclosed in a “pouch” that pinches off from the cell and becomes a membrane-bound vesicle. Two main types Pinocytosis- transports fluids or solutes Phagocytosis- transports large particles or whole cells.

Endocytosis – Phagocytosis The Plasma Membrane 11/24/2018 Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” G. Podgorski, Biol. 1010

Phagocytes Many unicellular organisms feed by the process of phagocytosis. Certain cells (Phagocytes) in animals use phagocytosis to ingest bacteria and viruses that invade the body.

Pinocytosis Most common form of endocytosis. The Plasma Membrane Pinocytosis 11/24/2018 Most common form of endocytosis. Takes in dissolved molecules as a vesicle. G. Podgorski, Biol. 1010

Exocytosis Process by which a substrate is released from the cell through a vesicle.

Homeostasis Cell transport Carrier Protein Is aided by which includes Such as Osmosis Diffusion Facilitated diffusion Is aided by Cell transport which includes Passive transport Of substance down their Active transport Of substances against their Endocytosis Exocytosis Sodium-potassium pump Concentration gradient Which use a Carrier Protein

Three Forms of Transport Across the Membrane The Plasma Membrane Three Forms of Transport Across the Membrane 11/24/2018 Active transport G. Podgorski, Biol. 1010