Homeostasis & Transport Chapter 8

Passive Transport Section 8.1

Homeostasis? How do cell membranes help maintain homeostasis within a cell? By controlling what goes into and out of the cell.

Passive Transport The movement of materials across a cell membrane WITHOUT the use of energy (ATP). Four Types: Diffusion Osmosis Facilitated Diffusion Ion Channels

Diffusion Movement of molecules from an area of high concentration to an area of low concentration.

Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW)

Concentration Gradient Difference in concentration of molecules across a space (or cell membrane). “Down the gradient” Movement from high to low concentration

Equilibrium When the concentration is EQUAL throughout the space (or on each side of the cell membrane) End of diffusion No NET movement, RANDOM movement still occurs

Diffusion of Liquids

Diffusion across a membrane Depends upon size, shape, and chemical makeup Easy to diffuse: Small Nonpolar

Osmosis WATER diffusion across a membrane “Down the gradient” Hypotonic solution to hypertonic solution Osmosis animation

Osmosis

Hypotonic Solution The solute concentration is higher inside the cell, the water concentration is higher outside the cell. Net movement = Water into the cell May cause Cytolysis

Hypertonic Solution The solute concentration is higher outside the cell, the water concentration is higher inside the cell. Net movement = Water out of the cell May cause Plasmolysis

Isotonic Solution The solute and water concentrations are EQUAL on both sides of the membrane. Equilibrium

Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic

hypotonic hypertonic isotonic hypertonic isotonic hypotonic

Facilitated Diffusion Use of carrier proteins the assist diffusion across a membrane. Specific carrier proteins for specific molecules (like glucose or amino acids) “Down the gradient”

Diffusion via ion channels Use of membrane proteins to assist diffusion of ions across a membrane Channel is usually specific to 1 type of ion Common ions: Sodium Potassium Chlorine Calcium

Notebook Quiz Osmosis is the diffusion of _____________. During diffusion, molecules tend to move in what direction? Does the movement of molecules stop once equilibrium is reached? Explain. What is the function of carrier proteins? If the external solution is hypotonic compared to the cell, which direction will water move?

Active Transport Section 8.1

Active Transport Uses energy (ATP) to move materials against the gradient “Up the gradient” Low to high concentration

1. Sodium Potassium Pump Transports sodium and potassium ions across the membrane up their gradients Low to high concentration Uses ATP

2. Endocytosis Movement of large amounts of material into the cell Formation of a vesicle from the cell membrane that will go to the lysosome for digestion Uses ATP

2 types of endocytosis 1. pinocytosis: “cell drinking” Transport of a large quantity of liquid into the cell 2. phagocytosis: “cell eating” Transport of a large quantity of solids into the cell Uses ATP

Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis.

3. Exocytosis The movement of a large amount of materials out of the cell Vesicle fuses to the cell membrane to release contents out of the cell Uses ATP

Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.

Passive & Active Transport Animation