Homeostasis & Transport Chapter 5

Passive Transport Section 5.1

Homeostasis  To remain alive and function optimally, cells must maintain a biological balance with their immediate environment called _______?

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

Cell Membrane Permeability What determines the permeability of a substance across the cell membrane? Size Polarity Hydrophobic vs. hydrophilic Charge

Permeability of Cell Membrane

Selectively Permeable The cell membrane is described as selectively permeable because it allows some substances to pass in or out but not others. The size, charge, and polarity of a substance determines its permeability. The cell membrane is permeable to gases such as carbon dioxide and oxygen since gases are small. The cell membrane is permeable to water and other small, polar molecules.

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

1. Diffusion Movement of molecules from an area of high concentration to an area of low concentration without the help of energy.

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 RANDOM movement still occurs

Diffusion of Liquids

Diffusion across a membrane Depends upon temperature, size, shape, and chemical makeup Easy to diffuse: Small (eg. O2 ) Nonpolar Hard to diffuse: Glucose amino acids

Diffusion and Equilibrium

Main Points Diffusion – molecules cross the cell membrane without using energy Always moves from higher concentration to lower concentration Ability to diffuse depends on size & type of molecule

2. Osmosis WATER diffusion across a membrane quickly “higher to lower concentration, DOWN THE GRADIENT Hypotonic solution to hypertonic solution

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

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

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

Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic

Cells deal with osmosis Cells live in isotonic environment – water moves with no problem Freshwater organisms – freshwater outside (hypotonic environment) of the cell makes too much water go into the cells because of osmosis, cells can burst

hypotonic hypertonic isotonic hypertonic isotonic hypotonic

Facilitated Diffusion movement of molecules that can’t diffuse by themselves through cell membrane Use of specific carrier proteins the assist diffusion across a membrane. (like glucose or amino acids) THIS IS HOW GLUCOSE ENTERS CELL RAPIDLY “Down the gradient” means high to low concentration

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 Some always open, some are “gated” Common ions: Sodium Potassium Chlorine Calcium

Active Transport Section 5.2

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 Complete cycle 3 Na +out & 2 K+ inside cell Low to high concentration Uses ATP

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

2 types of endocytosis 1. pinocytosis: “cell drinking” movement of a large quantity of solutes or liquid into the cell 2. phagocytosis: “cell eating” Movement of large solids or whole cells 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 removes wastes and cell products like proteins packaged by Golgi vesicles 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