Transport Across The Membrane

Transport Vocabulary Lipid Bilayer (phospholipid bilayer) Homeostasis   Lipid Bilayer (phospholipid bilayer) Homeostasis Passive Transport Diffusion Osmosis Facilitated Diffusion Selective Permeability Active Transport Endocytosis Exocytosis Isotonic Hypotonic Hypertonic Equilibrium

Cellular Transport Unit Passive Transport = movement of substances across the cell membrane without any input of energy by the cell

Passive Transport

Types 1) Diffusion = movement of molecules from high to low [ ] (concentration) - driven by the concentration gradient - spreads out evenly till dynamic equilibrium is reached

Diffusion

2) Osmosis = diffusion of water A solution may be one of the following: (compared to a cell) - isotonic solution: same [ ] of water and solute - hypotonic solution: lower [ ] of solute, a lot of water - hypertonic solution: higher [ ] of solute, less water

OSMOSIS

just remember that ...

Isotonic Solution (Red Blood Cells) A solution is isotonic to a cell if it has the same concentration of solutes as the cell. Equal amounts of water enter and exit the cell, so its size stays constant.

Hypotonic Solution (Red Blood Cells) A hypotonic solution has fewer solutes than a cell. Overall, more water enters a cell in a hypotonic solution, causing the cell to expand and even burst.

Hypertonic Solution (Red Blood Cells) A hypertonic solution has more solutes than a cell. Overall, more water exits a cell in a hypertonic solution, causing the cell to shrivel and even die

OSMOSIS Hypertonic Isotonic Hypotonic In Biology we usually talk about the SOLUTION’S tonicity, NOT the cells!

** Water tends to diffuse from hypotonic to hypertonic Direction of Osmosis Outside the Cell Inside the Cell Net Movement of Water Isotonic Isotonic None Hypotonic Hypertonic Inside the Cell Hypertonic Hypotonic Outside the Cell ** If the solution outside the cell is hypotonic, then inside the cell is hypertonic and vice versa ** Water tends to diffuse from hypotonic to hypertonic

- Plasmolysis = cells shrink when turgor pressure is lost - the reason plants wilt

VACUOLES store WATER TURGOR PRESSURE _____________________________ = http://www.biology4kids.com/files/cell_vacuole.html TURGOR PRESSURE _____________________________ = Pressure exerted by the movement of water during osmosis

- Cytolysis = cell bursts due to water entering the cell

3) Facilitated Diffusion = move molecules across the cell membrane through carrier/transport proteins - are specific for the type of molecule they help diffuse

Facilitated Diffusion (Open Channels)

Facilitated Diffusion (Proteins Change Shape)

Diffusion vs. Facilitated Diffusion Diffusion Facilitated Diffusion

Active Transport = substances can cross the cell membrane with an input of energy from the cell

requires ATP

Active Transport

1) Endocytosis = the process by which cells ingest “stuff” - vesicle holds the “stuff” - two types: 1) pinocytosis - solutes and fluids 2) phagocytosis - large particles or whole cells

Endocytosis Vesicle

phagocytosis

2) Exocytosis = the process by which cells release “stuff” - is essentially the reverse of endocytosis

Exocytosis Vesicle

Na+ and K + PUMP See a movie about Na+ - K+ pump Animation from: http://www.lionden.com/cell_animations.htm See a movie about Na+ - K+ pump Na+ exits cell K+ enters

PROTON PUMP H+ Moves Protons across membrane = ___ ions See a movie proton pump