32.A.3 – Organisms Must Exchange Matter With the Environment to Grow, Reproduce and Maintain Organization.Surface area-to-volume ratios affect a cell’s ability to exchange materials.As cells increase in volume, the relative surface area decreases and demand for material resources increases; more cellular structures are necessary to adequately exchange materials and energy with the environment. Limits cell size.Ex. Root hairs, alveoli cells, villi, microvilli
4The 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.
5SA/V Practice Problems Simple cuboidal epithelial cells lines the ducts of certain exocrine glands. Various materials are transported into or out of the cells by diffusion. The formula for the surface area of a cube is 6s2 and the formula for volume is s3 where s = length of the side of the cube. Which of the following cube-shaped cells would be most efficient in removing wastes by diffusion?40µm20µm30µm10µm
6Cells lining the kidneys are cuboidal Cells lining the kidneys are cuboidal. What is the SA/V of a kidney cell with a side length of 3.5µm?What would be the SA/V if cell (b) had a side that is 2.7µm?Which cell (a or b) would have an easier time with diffusion?What is the SA/V of a spherical liver cell with a diameter of 9.2µm?
72.B.1 – Cell Membranes Are Selectively Permeable Due to Their Structure Cell membranes separate the internal from the external environmentThe fluid mosaic model explains selective permeability of the membraneCell membranes consist of phospholipids, proteins, cholesterol, glycoproteins and glycolipidsPhospholipids have both hydrophobic and hydrophilic regions; fatty acids are oriented towards the middle and phosphate portions are oriented to the outsides
82.B.1 continued:Embedded proteins can be hydrophilic with charged and polar side groups, or hydrophobic with nonpolar side groups.Small, uncharged molecules (N2, O2,) and small hydrophobic molecules pass freely across the membrane; hydrophilic and ions move across through embedded channel and transport proteins. Water moves across through the membrane and through aquaporin proteins.
10Semi or Selectively Permeable CO2, O2, steroid hormones enter cells easily; conclusion?The membrane must be mostly made of _______Ions (Na+, Cl-, Ca++) proteins and larger molecules (glucose) move more slowly or not at all; conclusion?Cells must not need those molecules or ionsThe membrane must have (?) that enables that stuff to get in/out
18Kinetic Energy Molecules are in constant motion Kinetic energy is ‘free’ energy (usable)The greater the kinetic (free) energy, the ___ molecules can move.Molecules move ___ a concentration ___.
19Movement Across the Membrane Passive Transport – molecules have enough free energyDiffusionOsmosisFacilitated diffusionHydrostatic pressure/dialysisActive transport – against a concentration gradientPumps (proteins)Endo/exocytosis
202.B.2 – Growth and Dynamic Homeostasis Are Maintained By the Constant Movement of Molecules Across the Membrane.Passive transport requires no cellular energy; movement of molecules from high to low concentrationFacilitated diffusion through proteinsEx. Glucose, Na+/K+Hypertonic, hypotonic, isotonic
21Diffusion Kinetic (free) energy of molecules Down a concentration gradient until equilibriumHigher kinetic (free) energy = faster movementGases; small, uncharged moleculesIn solution**- membranes moistSA/V of lungs is ?
22Osmosis Diffusion of water through a semi-permeable membrane Cells are a solution, in a solutionCompare solutions:Hypertonic/hyperosmoticHypotonic/hypoosmoticIsotonic/isoosmotic**Important to understand concentration gradientWater moves from hypotonic to hypertonic
26Water PotentialMeasurement of the Potential of Water to Move Through a MembraneUseful for Mathematically Predicting Which Way Water Will Flow
27Water Potential What is potential ? Water Potential = ? Water flows from high water potential to low water potential till _____(?)***Water potential is expressed as Psi (Ψ)Psi is measured in MPa, atm, or barCar tire = 32 psi, 0.2 MpaSea level = 14.5 psi, 0.0MPa, 1 atm, 1 bar, 760mm Hg
28Water Potential Water Movement Force Down a hill Garden hose Fresh to saltyStraw
29Water Potential = Pressure Potential + Solute Potential Pressure potential: (p )Positive pressure, pushing like a hoseNegative pressure; sucking like a straw Major factor moving water through plantsSolute potential: (s)Reduction in water potential due to the presence of dissolved solutesSolutes take up space in the water (dilutes pure water)Solutions have lower water potential than pure water
30Water Potential Water potential (Ψ) = Ψp + Ψs Ψp – pressure potential (atmospheric pressure)Ψs – solute potential (osmotic pressure)The Ψp of atmosphere at sea level = 0 MPaThe Ψs of pure water = 0 MPaPure water at sea level = 0 MPa
31Solute Potential Solute Potential (Ψs ) = - iCRT i – ionization constantC – Concentration in MolesR – pressure constant ( literbars/mole-K)T – temperature in Kelvin (273 + oC)I = number of ions that will ionizeGlucose = 1NaCl = 2 (Na+, Cl-)
32Calculating Solute Potential (s) s = - iCRTEx. A 1.0 M sugar 22° C under standard atmospheric conditions:s = -(1)(1.0M)( L · bar )(295K)M · Ks = bars
33Adding solute to water lowers its water potential Solute molecules take up spaceEx. 0.1 M solution = MPaA 0.1 M solution at sea level:0 MPa (Ψp)MPa (Ψs)MPa = ΨΨp = 0+Ψs = 0
35Problem:A student calculates that the water potential of a solution inside a bag is:s = bar, p = 0 barAnd the water potential of the solution surrounding the bag is s = bar, p = 0 bar.In which direction will the water flow?Inside = bar; outside = barWater will flow into the bag. This occurs because there are more solute molecules inside the bag (therefore a value further away from zero) than outside in the solution.
41Water moves from soil into root cells because the cells have lower water potential due to the (Ψs) Soil or root?
42Proton PumpsTo maintain solute potential in their cells, plants use cotransport*Cotransport molecules are proteins
43Real life scenario: what happens with salt water intrusion or over-fertilization? Cell has More/Less water potential than soil?CellSoilPlasmolysis - cells lose water, become flaccid
44Additional Water Absorption by Roots SA/V increased by:Root hairsMycorrhizae - 90% of terrestrial plants
45Aquaporins Increase rate of water uptake Integral proteins in the membraneCongenital diabetes insipidus (?) – mutation
46Facilitated Diffusion Glucose moves faster through membranes than diffusion can account for (?)Diffusion through proteinsMay require a receptorInsulin/glucose – what is diabetes?highered.mcgraw-hill.com
47Hydrostatic Pressure Pressure created by blood - (Ψp) Glomerulus of the kidney - dialysis
48Moving Molecules Against a Gradient Active TransportMoving Molecules Against a GradientIonsLarge Molecules
49Cell MembraneIons, polar molecules, large molecules move slowly or not at allIntegral proteins enable movement of specific molecules across the membraneShape determines functionProtein shape is sensitive to change (homeostasis)
502.B.2 Active transport requires free energy (ATP) Establish and maintain concentration gradientsMoves molecules and ionsNeeds membrane proteinsEndocytosis and exocytosis move large molecules (use of vesicles)
51Active Transport Nerve cells: Na+ K+ ion pump Membrane potential - difference in electrical charge across a membraneElectrochemical gradientCosts the cells ___(?)
52Co-TransportPassing of molecules against their concentration gradient using energy from another molecule’s energyPlants: proton ‘pump’
53Down the concentration gradient Against the concentration gradient Channel proteinDown the concentration gradientCarrier proteinAgainst the concentration gradient