Moving Substances Across Cell Membrane cell membrane is semi–permeable Some molecules pass through easily, some need help Some molecules pass through without the expenditure of energy (spontaneous) and some require an input of energy (ATP) What molecules move IN and OUT of a cell: Small nonpolar molecules (CO2, O2) Small polar molecules such as water Ions and charged molecules Large polar molecules (eg. Glucose) Macromolecules Movement IN and OUT can Be PASSIVE or ACTIVE

Passive Transport [High][Low] cell uses no energy molecules move randomly Molecules spread out from an area of high concentration to an area of low concentration. [High][Low] Three types: Diffusion Facilitative Diffusion Osmosis high low Weeee!!!

Simple Diffusion Animation Passive Transport: Diffusion: random movement of particles from an area of [high] to an area of [low]. diffusion continues until all molecules are evenly spaced (equilibrium is reached)- Note: molecules will still move around but stay spread out. http://bio.winona.edu/berg/Free.htm

Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Passive Transport: A B 2. Facilitated diffusion: diffusion of particles from [H  L] through transport proteins found in the membrane Transport Proteins are specific – they “select” only certain molecules to cross the membrane Facilitated diffusion (Channel Protein) Diffusion (Lipid Bilayer) Carrier Protein http://bio.winona.edu/berg/Free.htm

Passive Transport: Osmosis animation 3.Osmosis: diffusion of water through a selectively permeable membrane from an area of [H  L] Water moves freely through pores. Solute (green) too large to move across.

Effects of Osmosis on Life Water molecules are so small and so numerous that cells can’t control movement of water through the cell membrane. So what determines the direction of water movement? The environment around the cell, …specifically, the concentration of water molecules inside the cell compared to outside Environment around the cell is either: HYPOTONIC, ISOTONIC, HYPERTONIC

But first - Don’t confuse Volume of water with Concentration Equal Volumes, Different Concentration

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypotonic: The external environment (ECF) has a lower concentration of solutes and a higher concentration of water than inside the cell. Result: Water moves from the ECF to inside the cell - Cell Swells and bursts open (cytolysis)!

Compare a blood cell in an isotonic environment with one in a hypotonic environment

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Isotonic Solution Isotonic: The concentration of solutes in the ECF is equal to the concentration of solutes inside the cell. Result: Water moves equally in both directions and the cell remains same size. (Dynamic Equilibrium)

Water on the way out

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions Hypertonic Solution Hypertonic: The ECF has a higher concentration of solutes and a lower concentration of water than inside the cell. shrinks Result: Water moves from inside the cell into the solution: Cell shrinks. Plasmolysis (plant cell) Crenation (animal cell)

B C A In what type of solution are these cells? Hypertonic Isotonic Plant cells resist bursting. Why? Hypertonic Isotonic Hypotonic

Active Transport cell uses energy Animations of Active Transport & Passive Transport Active Transport cell uses energy actively moves molecules to where they are needed Movement of molecules from an area of [low] to an area of [high] Three Types Protein Pumps Endocytosis Exocytosis high low This is gonna be hard work!!

Types of Active Transport Sodium Potassium Pumps (Active Transport using proteins) 1. Protein Pumps –are special transport proteins that help move molecules IN/OUT - require energy to do work example: Na+/K+ Potassium Pumps are important in nerve responses. Protein changes shape to move molecules: this requires energy!

Types of Active Transport 2. Endocytosis: taking bulky material into a cell Uses energy Cell membrane folds itself around food particle “cell eating” forms food vacuole & digests food This is how white blood cells eat bacteria!

Types of Active Transport 3. Exocytosis: Forces material out of cell in bulk membrane surrounding the material fuses with cell membrane Cell changes shape – requires energy EX: Hormones or wastes released from cell Endocytosis & Exocytosis animations

Endocytosis_[www.keepvid.com].mp4 Active_Transport_~~_[www.keepvid.com].mp4