Thursday November 20 Objectives You will be able to: – Explain the concept of diffusion and how it...
Transcript of Thursday November 20 Objectives You will be able to: – Explain the concept of diffusion and how it...
Thursday November 20
• Objectives You will be able to:– Explain the concept of diffusion and how it relates to cells– Describe the different ways that molecules can be passively
transported across the cell membrane• Agenda
– Reading Quiz– Start Notes on Passive Transport (Chapter 5-1)
• Homework Due today– Read section 5-1– Outline of section
Passive Transport
Section 5-1
Passive Transport
• Doesn’t require energy• Concentration is the amount of solute
dissolved in a fixed amount of solvent• Concentration gradient is the difference in the
concentration across space
Diffusion
• Diffusion - the movement of molecules from high concentrations to low concentrations– Molecules are in constant motion (kinetic energy)– This movement drives diffusion
Equilibrium
• Concentration is the same throughout– Solutions move to equilibrium
• Even at equilibrium, molecules are still moving– Movement in many directions balances
concentration
Diffusion Across Membranes
• Some molecules can move from high concentration to low across the cell membrane– Depends on size, shape, and nature
• Molecules that dissolve in lipids can move across the membrane– Molecules that don’t must move through protein
pores
Osmosis• Water moving across a membrane• Hypotonic is when the solute concentration outside is lower
(water moves in- cell expands) • Hypertonic is when the solute concentration outside is higher
(water moves out- cell shrinks)• Isotonic is when concentrations are equal
HypOtonic
Inside
Outside
HypERtponic
Inside
Outside
Osmosis in Cells• Hypotonic environment– Contractile vacuole- collects water and pumps out– Plants use cell wall- holds up against turgor
pressure (the pressure water exerts)– Some pump solutes out of cytosol– Cytolysis (bursting) (red blood cells)
• Hypertonic environment– Plant cell membrane shrinks against cell wall
(plasmolysis), plant wilts– Red blood cells shrink and shrivel
PlantsHypotonic environment
Hypertonic environment
Red Blood Cells
Facilitated Diffusion
• Carrier proteins help some molecules that cant diffuse rapidly through the membrane
• Not soluble in lipids, or too large– Still diffusion because moving from high to low
• Molecule binds to protein, shields it from the hydrophobic cell membrane, and releases to other side of the cell– Carrier molecule is specific to molecule• Example: glucose
Ion Channels
• Provide passage for ions that can’t diffuse on their own (not soluble)
• Specific to each ion (Na+ K+ Ca2+ Cl-)• Some are always open but some have gates
that respond to:– Stretching of cell membrane– Electrical signals– Chemicals in cytosol or environment
Active Transport
Section 5-2
Sodium Potassium Pump• Same as passive transport but from low to high• NA+ binds to a carrier protein from inside• Phosphate from ATP changes shape of the protein• New shape allows K+ to bind to protein (outside)
and phosphate leaves• Loss of phosphate changes shape again and K+ is
released into the cell• Inside becomes negative while outside becomes
positive-– conducts electrical impulses
Endocytosis
• Cells ingest external fluid, macromolecules, and large cells
• Materials enclosed by cell and pinched off into a vesicle– Can fuse with organelles and digested
• Pinocytosis involves fluid• Phagocytosis involves large particles– Phagocytes ingest bacteria and viruses • destroyed by lysozymes
Exocytosis
• The reverse of endocytosis• Vesicles fuse with cell membrane and contents
are released into the environment• Used to export large molecules such as
proteins