Cellular Processes and structure 03 Cell Structure Osmosis Cell Membrane Membrane Transport Eukaryotic cells

Osmosis AP Bio Framework: 2.A.2 Holtzclaw: 44(6.2), 52(7.3), 207, 208(36.2) Campbell: 6.2, 7.3, 36.2

Surface area-to-volume ratios affect diffusion across the membrane As cells increase in volume, the relative surface area decreases.

Surface area-to-volume ratios affect diffusion across the membrane (cont.) Problem: demand resources increases, but larger cell are less efficient Solution: specialized cellular structures

Surface area-to-volume ratios affect diffusion across the membrane (cont.) root hairs alveoli

The surface area of the plasma membrane must be large enough to adequately exchange materials smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment.

Osmosis Across a membrane, water moves from areas of low solute concentration, to areas of high solute concentration

Water Potential  = P + S P = pressure potential pressure exerted by the water on the cell wall/membrane S = solute potential The effect of solute concentration If  of a cell is negative, water flows into the cell

Water Potential ΨS = – iCRT i = ionization constant (For sucrose this is 1.0 because sucrose does not ionize in water.) C = molar concentration R = pressure constant (R = 0.0831 liter bars/mole K) T = temperature in Kelvin (273 + ºC)

Water Potential  = P + S

If a cell’s ΨP = 2 bars and its ΨS = -3 If a cell’s ΨP = 2 bars and its ΨS = -3.5 bars, what is the resulting Ψ? The cell from question #1 is placed in a beaker of sugar water with ΨS = -4.0 bars. In which direction will the net flow of water be? The value for Ψ in root tissue was found to be -3.3 bars. If you place the root tissue in a 0.1 M solution of sucrose at 20°C in an open beaker, what is the Ψ of the solution, and in which direction would the net flow of water be?

Be able to 2.6 Use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion. 2.7 Explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination. 2.8 Use data to justify the types of molecules that an animal, plant or bacterium will take up as necessary building blocks and excrete as waste products.

Be able to 2.9 Use graphs or models to demonstrate the following exchange of molecules between an organism and its environment the use of these molecules to build new molecules the use of these molecules to maintain dynamic homoeostasis, growth and reproduction.