Diffusion, Osmosis and Active Transport

Diffusion

The net movement of particles from an area of high concentration to an area of low concentration (can move both ways, but net movement is to lower)

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Diffusion- passive process

No energy is needed, particles can diffuse directly across cell membranes , this is simple diffusion

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Factors effecting rate of diffusion

Concentration gradient, thickness of exchange surface, surface area

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Concentration Gradient

higher the CD the faster the rate of reaction. As diffusion takes place, difference in concentration between different side of membrane decreases until reaches equilibrium (equal concentration)

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Thickness of exchange surface

Thinner exchange surface = faster diffusion rate

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Surface Area

larger SA= faster rate of diffusion

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Facilitated Diffusion

The diffusion of larger molecules or charged particles through carrier or channel proteins in the membrane . Move from high to low concentration gradient , also a passive process

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Carrier Proteins

CP move large molecules across membranes. 1. large molecule attaches to carrier protein 2. protein changes shape 3. this releases molecule on opposite side of membrane

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Channel proteins

ChP form pores in membrane for charged particles to diffuse through

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Calculating rate of diffusion

Can be asked to calculate from a graph. For straight line, find gradient. For curved graph, draw tangent and find gardient

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Osmosis

Diffusion of water molecules across partially permeable membrane from high to low water potentail

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Water Potential (WP)

The likelihood of water molecules to diffuse in or out of a solution

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Water molecules

Water molecules are small and diffuse easily through a cell membrane, large solute molecules cant

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Pure Water

has a WP of zero, adding solutes to pure water lowers WP so WP of any solution is always negative. The more negative the WP, the stronger the concentration of solutes in solution

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Isotonic Solutions

2 solutions that have the same WP. Cells in an isotonic solution wont lose or gain any water - not net movement of molecules

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HypOtonic Solutions

Solutions with a higher WP compared with the inside of the cell

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HypERtonic Solutions

If a cell is placed in a solution that has a lower WP it may shrink as water moves out by osmosis

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Factors Affecting rate of Osmosis

WP gradient (higher WP = faster osmosis, levels off over time), Thickness of exchange surface (thinner surface = faster osmosis), Surface area (larger SA = faster osmosis)

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Investigating WP

can use potato cylinders to investigate WP. 1) make serial dilutions - 0.5%, 0.25% and 0.125% 2) measuring change in mass (PTO)

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Measuring change in mass

> cut 1cm diameter chips and place in groups of 3 and measure mass. Place one group into each sucrose solution and leave for 20 mins . Remove and dry. Weigh each group again and record. Calc. % change . Chips will gain water in sol. w/ high WP

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Producing calibration curve

plot percentage change in mass against concentration of sucrose solution

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Active Transport

AT uses engergy to move molecules and ions across plasma membranes, usually against con. grad. Carrier proteins and co-transport are involved in AT

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AT Carrier Proteins

Molecule attaches to CP, CP changes shape, moves molecule across membrane and releases on other side

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Differences between AT and Facilitated Diffusion

AT moves solutes from low>high, FD its always high>low. AT requires energy, FD is passive

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ATP in AT

ATP is a common source of energy in cell so important for AT. Undergoes hydrolysis to become ADP and P. Releases energy so solutes can be transported

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Co-Transporters

Type of carrier protein, bind 2 molecules at a time. Con. grad. of one is used to move the other molecule against its own con. grad.

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Co-transportation and absorption of Glucose I

Sodium ions actively transported out of epithelial into blood -creates con. grad. high con. of sodium ions in lumen of ileum (end of small intestine) than inside the cell. Causes sodium ions to diffuse from lumen into epithelial , PTO

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Co-transportation and absorption of Glucose II

down the con. grad. via the co-transporter proteins. Co-T carries glucose into cell with sodium. Glucose diffuses out of cell into blood, down its con. grad. through a protein channel, by facilitated diffusion

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Factors Affecting rate of Active Transport

Speed of carrier proteins (faster they work = faster AT), number of carrier proteins (more proteins = faster AT), rate of respiration and availability of ATP (is respiration is inhibited = AT cant take place)

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Diffusion, Osmosis and Active Transport

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