7-3 Cell Transport

REVIEW Regulates what enters and leaves the cell Protects and supports the cell Composed of Lipids = bilayer Proteins = channels Carbs = identification cards

Different types of movement Passive Transport Diffusion Osmosis Facilitated Diffusion Active Transport Membrane Pumps Endo/Exocytosis

PASSIVE TRANSPORT – Diffusion “passive” = no energy required Molecules in Motion Molecules are in constant motion Move from a region where they are more numerous (high concentration) to where they are less numerous (low concentration) Want to reach a state where molecules are spread out evenly = EQUILIBRIUM

PASSIVE TRANSPORT – Diffusion “passive” = no energy required Diffusion – the process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration Factors that contribute to movement of substances: Unequal concentrations Permeability The cell membrane is selectively permeable – allowing some things to cross while others cannot

2. PASSIVE TRANSPORT - Osmosis Most molecules cannot dissolve in the lipid bilayer of the cell; therefore, they cannot pass through - BUT – WATER CAN… Osmosis – diffusion of water across a selectively permeable membrane

Osmotic pressure – the force exerted by osmosis Water will pass through the membrane from a area of high water concentration to an area of low water concentration There is a net movement of water from where there is less solute to where there is more solute (in an attempt to dilute it) Osmotic pressure – the force exerted by osmosis Types of tonicity (the ability of a substance to draw water towards it)

Isotonic Solution “Iso” = the same Water will move both ways in equal amounts Why is important that contact lens solution is isotonic?

Hypotonic Solution "Hypo" = less Less solute (salt) molecules outside the cell Water will move in both directions BUT more water will move into the cell causing it to grow larger (cytolysis) In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid (turgid), the cell wall keeps the plant from bursting In animal cells, the cell may be in danger of bursting, organelles called CONTRACTILE VACUOLES (only on paramecium) will pump water out of the cell to prevent this

Hypertonic Solution "Hyper" = more More solute (salt) molecules outside the cell Water will move in both directions BUT more will move out of the cell causing it to shrink (plasmolysis) In plant cells, the central vacuole loses water and the cells shrink, causing wilting (loss of turgor pressure) In animal cells, the cells shrink In both cases, the cell may die Why is it dangerous to drink sea water? This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages

Which type of solution is it? A B C

1. What type of solution is this “cell” in? a: hypotonic solution 2. What will happen to this “cell” over time? a: the cell will expand and possibly burst = CYTOLYSIS

3. PASSIVE TRANSPORT - Facilitated Diffusion No energy required Carrier proteins transport molecules across the membrane (from high to low concentrations) Molecules may be too big or cells may need to get the molecules quickly

4. ACTIVE TRANSPORT Requires energy (usually ATP) Move molecules against the concentration gradient – the opposite direction of passive transport

4. ACTIVE TRANSPORT - Membrane Pumps Transport macromolecules move molecules across the cell membrane Requires ENERGY Examples – calcium, potassium, sodium ions

5. ACTIVE TRANSPORT – Endocytosis vs. Exocytosis Endocytosis – taking materials into the cell by infoldings of the cell membrane Phagocytosis – when large particles (food, microorganisms) are taken into the cell Pinocytosis – when liquids or relatively small particles (solutes) are taken into the cell Receptor-mediated endocytosis

Exocytosis – when large molecules are removed from the cell Contractile vacuoles – water is pumped out of the cell so it doesn’t burst

concentration gradient facilitated diffusion active transport concentration gradient energy facilitated diffusion particles/water