Transportation of substances across a cell membrane

[A] Passive Transport Spontaneous – does not require energy eg. rocks rolling down a hill Three types: Diffusion Osmosis Facilitated Diffusion

1. Diffusion The movement of molecules from a region of high concentration to a region of low concentration Molecules move down the concentration gradient

Diffusion and the Living Cell Cell membrane acts as a barrier which allows certain things into the cell and certain things out Selectively Permeable Membrane eg. O2 diffuses into a cell and CO2 diffuses out Like your hearing!

Equilibrium Pg. 89 Fig 1

Selectively Permeable Impermeable Does not allow molecules to pass Permeable Allows molecules to pass freely Selectively Permeable Permits some molecules and controls others

2. Facilitated Diffusion Diffusion across a membrane at a rate faster than normally expected Some form of assistance (protein molecule)

Transport proteins: 2 Types Channel protein Aqueous channel allows polar molecules and ions to pass Some open all the time, some have gates that respond to different signals (eg. hormones, electric charges, pressure, or light) Cystic fibrosis is a result of defective chloride ion channel protein

Carrier protein Bind specifically to molecules they assist Similar to an enzyme binding to its substrate Has lower rates of diffusion compared to channel protein because they can only bind to a few molecules at once Cystinurea (painful stones that block the urinary tract) is a result of the inability of a carrier protein to remove cystine and amino acids from urine Pg. 91 Fig 4

3. Osmosis Diffusion of water from a high concentration to a low concentration across a semi-permeable membrane Concentration: measure of amount of solute in a solution Solution: combination of solvent with one or more solutes Solvent: part of a solution that the solute dissolves (eg. water) Solute: part of a solution that becomes dissolved (eg. salt)

Isotonic solution A solution that has the same solute concentration as another solution

Hypertonic solution A solution that has a higher solute concentration than another solution

Cell in a hypertonic solution

Hypotonic solution A solution that has a lower solute concentration than another solution

Cell in a hypotonic solution

In animal cells: under hypotonic conditions the cell may HEMOLYSIS (burst) under hypertonic conditions the cell may undergo CRENATION (shrink) In plant cells: under hypotonic conditions the cell becomes TURGID (bulges) under hypertonic condition the cell may PLASMOLYSIS (pull away from cell wall) Turgor Pressure – osmosis in plants where water accumulates in vacuoles causing pressure on the cell wall

p. 92 Fig 6

[b] Active Transport Cells must use energy (ATP) Moves substances against a concentration gradient (up hill)

[C] Membrane Assisted Transport Similar to active transport – requires energy Two forms: Endocytosis Exocytosis

1. endocytosis Cell engulfs material by folding the cell membrane around it and forms a vesicle inside the cell Three methods Phagocytosis Pinocytosis Receptor mediated endocytosis

phagocytosis ‘Cell eating’ Taking in of discrete particles or fragmented matter Pg. 96 Fig 11

pinocytosis ‘Cell drinking’ Taking in of liquids Pg. 96 Fig 11

Receptor-mediated endocytosis Uses receptor proteins on cell membrane to bind with specific molecules. Outside layer is created with protein  coated pit Pg. 96 Fig 12

2. exocytosis Macromolecules and other large particles leaving cell Products to be released, or waste material, are contained in a vesicle that fuses with the cell membrane and empties contents in extra cellular environment In plant cells  helps construct the cell wall In animal cells  secretes hormones, neurotransmitters, digestive enzymes, etc

Pg. 95 Fig 10

Section 2.4 Answer p. 97 #3, 4, 9 Answer SG 2.4 #1-3, 8, 9