Active and Passive Transport

1. Passive Transport Movement of materials in and out of the cell Requires no energy to happen

Two Types of Passive Transport 1. Diffusion: When substance moves that is dissolved in water 2. Osmosis: When water moves across the membrane

Diffusion Move from HIGH to LOW concentration – directly through membrane simple diffusion no energy needed – help through a protein channel facilitated diffusion (with help) no energy needed HIGH LOW

Simple vs. facilitated diffusion inside cell outside cell lipid inside cell outside cell H2OH2O simple diffusionfacilitated diffusion H2OH2O protein channel

Active transport Cells may need molecules to move against concentration “hill” – need to pump “uphill” from LOW to HIGH using energy – protein pump – requires energy ATP

Transport summary simple diffusion facilitated diffusion active transport ATP

Solutions are made of 2 parts: Solute: Substance that is dissolved in water (eg. salt, sugar, etc.) Solvent: Liquid it is dissolved in (usually water)

(a) (b) Osmosis Molecules of dye Membrane (cross section) WATER Net diffusion Equilibrium Net diffusion Equilibrium

Lower concentration of solute (sugar) Higher concentration of sugar Same concentration of sugar Selectively permeable mem- brane: sugar mole- cules cannot pass through pores, but water molecules can More free water molecules (higher concentration) Water molecules cluster around sugar molecules Fewer free water molecules (lower concentration) Water moves from an area of higher free water concentration to an area of lower free water concentration  Osmosis

Describing a solution 1. Hypotonic: when a solution is less concentrated than another solution Example: if around a cell is hypotonic, then water will move into the cell. Can cause a cell to get so large it may burst (cytolysis)

2. Hypertonic: When a solution is more concentrated than another solution If around a cell is hypertonic, water will move out of the cell Can cause the cell to get very small (in plants will see plasmolysis: wilting)

3. Isotonic: when two solutions have the same concentration (are at equilibrium) Causes water to move in and out equally The cell maintains its shape

Hypotonic solutionIsotonic solution Hypertonic solution (a) (b) H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2O H2OH2O Lysed NormalShriveled Turgid (normal)Flaccid Plasmolyzed

How does this apply to our french- fries? We had 3 solutions: – No NaCl Got heavier, larger, and more turgid Hypotonic solution – 0.9% NaCl Basically no change in any way Isotonic solution – 10% NaCl Got shriveled, lost water and weight, got floppy Hypertonic solution

Hypotonic solutionIsotonic solution Hypertonic solution (a) (b) H2OH2OH2OH2O H2OH2OH2OH2O H2OH2OH2OH2O H2OH2O H2OH2O Lysed NormalShriveled Turgid (normal)Flaccid Plasmolyzed

2. Osmosis Water moves trying to balance out concentrations Goes from where there is more water to less water

What if….. Environment around a cell is hypotonic. What direction will the water move? Salt?

What if….. The environment around a cell is hypertonic. What direction will the water move? Salt?

2. Active Transport Requires energy Goes against the concentration gradient (from lower concentration to higher concentration)

Figure 7.16 The sodium- potassium pump: a specific case of active transport Cytoplasmic Na + binds to the sodium-potassium pump. 1 Na + binding stimulates phosphorylation by ATP. 2 K + is released and Na + sites are receptive again; The cycle repeats. 3 Phosphorylation causes the protein to change its conformation, expelling Na + to the outside. 4 Extracellular K + binds to the protein, triggering release of the Phosphate group. 6 Loss of the phosphate restores the protein’s original conformation. 5 EXTRACELLULAR FLUID [Na + ] high [K + ] low CYTOPLASM [Na + ] low [K + ] high Na + P ATP Na + P ADP P P i K+K+ K+K+ K+K+ K+K+ K+K+ K+K+

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Sodium Potassium Pump Cells usually have more sodium ions outside and more potassium ions inside Pump increases number of ions where concentration is already high

When substances are too large to pass through the cell membrane, use endocytosis or exocytosis Membrane folds around substances and release into cell or out of cell

Figure 7.20 Exploring Endocytosis in Animal Cells EXTRACELLULAR FLUID Pseudopodium CYTOPLASM “Food” or other particle Food vacuole 1 µm Pseudopodium of amoeba Bacterium Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM). PHAGOCYTOSIS PINOCYTOSIS Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM). 0.5 µm Plasma membrane Vesicle

Endocytosis Material moved into cell Forms vesicle 1. Pinocytosis: Liquids 2. Phagocytosis: Solids

Exocytosis Material released to outside of cell