CHAPTER 5 – HOMEOSTASIS + TRANSPORT 5-1: PASSIVE TRANSPORT 5-1: PASSIVE TRANSPORT 5-2: ACTIVE TRANSPORT 5-2: ACTIVE TRANSPORT

5-1: PASSIVE TRANSPORT Cell membranes help organisms maintain homeostasis by controlling what substances go in or out of cells. Cell membranes help organisms maintain homeostasis by controlling what substances go in or out of cells. Some substances can cross the cell membrane without any input of energy – known as passive transport Some substances can cross the cell membrane without any input of energy – known as passive transport Let’s look at some types of passive transport… Let’s look at some types of passive transport…

Diffusion Diffusion – movement of molecules from high concentration to low concentration Diffusion – movement of molecules from high concentration to low concentration Difference in the concentration of molecules across a space is called the concentration gradient Difference in the concentration of molecules across a space is called the concentration gradient –Ex. Sugar in Water

Look at the Example

Diffusion (cont.) Diffusion is driven by kinetic energy – nrg of motion – molecules in constant, involuntary motion Diffusion is driven by kinetic energy – nrg of motion – molecules in constant, involuntary motion Molecules move down their concentration gradient (High to Low) Molecules move down their concentration gradient (High to Low)

Equilibrium When there are no other influences, diffusion will inevitably cause the concentration of molecules to even out the space - - known as EQUILIBRIUM When there are no other influences, diffusion will inevitably cause the concentration of molecules to even out the space - - known as EQUILIBRIUM At equilibrium, there is no concentration gradient - - the molecules can move in any direction (Randomly) At equilibrium, there is no concentration gradient - - the molecules can move in any direction (Randomly)

Simple Diffusion Cell membrane controls what goes in and out – Selectively Permeable Cell membrane controls what goes in and out – Selectively Permeable Molecules will go from area of greater concentration to an area of lower concentration Molecules will go from area of greater concentration to an area of lower concentration

What types of molecules can cross a C.M.? Depends on 3 characteristics: Depends on 3 characteristics: –Size of molecule –Type of molecule –Chemical nature of C.M. –Examples:  Amino Acids  CO 2 O2O2O2O2 H2OH2OH2OH2O

Osmosis Solution = Solute dissolved in a solvent Solution = Solute dissolved in a solvent Osmosis – the process by which water molecules move from High to Low through a cell membrane Osmosis – the process by which water molecules move from High to Low through a cell membrane –*No nrg – Passive Transport

Direction of Osmosis The net direction of osmosis depends on the relative concentration of solutes on the two sides of the membrane The net direction of osmosis depends on the relative concentration of solutes on the two sides of the membrane

Types of Osmotic Environments Hypotonic – when solute concentration outside the cell is lower than the solute concentration in the cytosol Hypotonic – when solute concentration outside the cell is lower than the solute concentration in the cytosol –Water moves into cell –Cell swells until equilibrium is reached

Types of Osmotic Environments Hypertonic – when the solute concentration outside cell is higher than solute concentration in cytosol Hypertonic – when the solute concentration outside cell is higher than solute concentration in cytosol –Water leaves the cell –Cell shrinks until equilibrium is reached

Types of Osmotic Environments Isotonic – when solute concentration inside = solute concentration outside Isotonic – when solute concentration inside = solute concentration outside –Water moves in + out at same rate = no net movement of water –Cell stays same size

RBCs in Solutions

How Cells deal w/ Osmosis Contractile Vacuoles – organelles that remove excess water Contractile Vacuoles – organelles that remove excess water –Used by unicellular organisms (protists) that live in hypotonic environments –Collects water and “pumps” it out into the environment –“pumping” requires nrg

How Cells deal w/ Osmosis Turgor Pressure – pressure water molecules exert against the cell wall Turgor Pressure – pressure water molecules exert against the cell wall –If turgor pressure decreases, plasmolysis may occur –If turgor pressure increases, cytolysis may occur

Plasmolysis

Cytolysis

Facilitated Diffusion Used for molecules that cannot readily diffuse through cell membranes Used for molecules that cannot readily diffuse through cell membranes Uses Carrier Proteins to assist the movement of molecules down their concentration gradient Uses Carrier Proteins to assist the movement of molecules down their concentration gradient Example molecule - Example molecule - GLUCOSE

How F.D. works 1. Carrier protein binds to molecule on outside of C.M. 2. Carrier protein changes shape + shields molecule from interior of C.M. 3. Carrier protein releases molecule inside the cell 4. Carrier protein returns to normal shape and is available to transport another molecule

Two Properties of FD 1. Helps substances move in or out depending on concentration gradient 2. Carrier proteins are specific to types of molecules they move

Diffusion through Ion Channels Ion channels move ions from High to Low Ion channels move ions from High to Low –Important ions: Ca +, Na +, K +, Cl - –Channels are specific for each ion they transport

Open vs. Gated Ion Channels Open – always open Open – always open Gated – may open or close due to: Gated – may open or close due to: –Stretching of C.M. –Electrical signals –Chemicals in environment

Passive Transport Video Video Recap Video Recap Video Recap Video Recap