AP Biology Movement across the Cell Membrane

AP Biology Diffusion  Diffusion  movement from HIGH  LOW concentration  Diffusion  movement from HIGH  LOW concentration

AP Biology Simple Diffusion  Move from HIGH to LOW concentration  “passive transport”  no energy needed diffusionosmosis movement of water

AP Biology Osmosis is just diffusion of water  Water is very important to life, so we talk about water separately  Diffusion of water from HIGH concentration of water to LOW concentration of water  across a semi-permeable membrane

AP Biology freshwaterbalancedsaltwater Managing water balance  Cell survival depends on balancing water uptake & loss

AP Biology Concentration of water  Direction of osmosis is determined by comparing total solute concentrations  Hypertonic - more solute, less water  Hypotonic - less solute, more water  Isotonic - equal solute, equal water hypotonichypertonic water net movement of water

AP Biology Managing water balance  Hypotonic  a cell in fresh water  high concentration of water around cell  problem: cell gains water, swells & can burst  example: Paramecium  ex: water continually enters Paramecium cell  solution: contractile vacuole  pumps water out of cell  ATP  plant cells  turgid = full  cell wall protects from bursting freshwater ATP 1

AP Biology Pumping water out  Contractile vacuole in Paramecium ATP

AP Biology Managing water balance  Hypertonic  a cell in salt water  low concentration of water around cell  problem: cell loses water & can die  example: shellfish  solution: take up water or pump out salt  plant cells  plasmolysis = wilt  can recover saltwater 2

AP Biology Managing water balance  Isotonic  animal cell immersed in mild salt solution  no difference in concentration of water between cell & environment  problem: none  no net movement of water flows across membrane equally, in both directions  cell in equilibrium  volume of cell is stable  example: blood cells in blood plasma  slightly salty IV solution in hospital balanced 3

AP Biology  Water moves from:  High Water Potential → Low Water Potential  Low Solute Conc. → High Solute Conc.  Hypotonic Soln. → Hypertonic Soln.  Low Osmotic Poten. → High Osmotic Poten. solution. Osmotic Potential: tendency to H 2 O to move across a membrane into a solution.

AP Biology Aquaporins  Water moves rapidly into & out of cells  evidence that there were water channels  protein channels allowing flow of water across cell membrane 1991 | 2003 Peter Agre John Hopkins Roderick MacKinnon Rockefeller

AP Biology Cell (compared to beaker)  hypertonic or hypotonic Beaker (compared to cell)  hypertonic or hypotonic Which way does the water flow?  in or out of cell.05 M.03 M Do you understand Osmosis…

AP Biology Facilitated Diffusion  Diffusion through protein channels  channels move specific molecules across cell membrane  no energy needed open channel = fast transport facilitated = with help HIGH LOW

AP Biology Active Transport conformational change  Cells may need to move molecules against concentration gradient  conformational shape change transports solute from one side of membrane to other  protein “pump”  “costs” energy = ATP ATP LOW HIGH

AP Biology symportantiport Active transport  Many models & mechanisms ATP

AP Biology Active transport  Movement of molecules against the concentration gradient. Requires Energy!

AP Biology

Getting through cell membrane  Passive Transport  Simple diffusion  diffusion of nonpolar, hydrophobic molecules  lipids  HIGH  LOW concentration gradient  Facilitated transport  diffusion of polar, hydrophilic molecules  through a protein channel  HIGH  LOW concentration gradient  Active transport  diffusion against concentration gradient  LOW  HIGH  uses a protein pump  requires ATP ATP

AP Biology Transport summary simple diffusion facilitated diffusion active transport ATP

AP Biology Osmoregulation  Regulates solute concentrations and balances the gain and loss of water.

AP Biology  Marine fish are hypotonic to sea water  They lose water by osmosis and gain salt by diffusion from food  They balance water loss by drinking seawater and excreting salts

AP Biology  Freshwater animals constantly take in water by osmosis from their hyoptonic environment  They lose salts by diffision and maintain water balance by excreting large amounts of dilute urine.  Salts lost by diffusion are replaced in foods and by uptake across the gills.

AP Biology  The kidneys are the principle site of water balance and salt regulation.

AP Biology The Nephron consists of a single long tubule and ball of capillaries called the glomerulus. Bowman’s capsule surrounds and receives filtrate from the glomerulus.

AP Biology  The filtrate will flow through three regions of the nephron. 1. Proximal Tubule 2. Loop of Henle 3. Distal Tubule

AP Biology Filtration Blood pressure forces fluid from the blood in the glomerulus into the Bowman's capsule This is a nonselective process. The filtrate contains salts, glucose, amino acids, vitamins, nitrogenous wastes and ofher small molecules.

AP Biology Reabsorption Ions, water and nutrients are reabsorbed. These are actively and passively transported from the filtrate into the interstitial fluid and then capillaries. Toxic materials are secreted.

AP Biology Descending Loop Reabsorption of water continues through channels formed by aquporin proteins. Movement is driven by the hypertonic interstitial fluid. The filtrate becomes increasingly concentrated.

AP Biology Ascending Loop Salt but not water is able to diffuse from the tubule into the interstitial fluid. The filtrate becomes increasingly dilute.

AP Biology Distal Tubule Regulates the K + and NaCl concentrations of body fluids.

AP Biology Collecting Duct Water is lost as well as some salt and urea, and the filtrate becomes more concentrated Urine is hypertonic to the body fluids.

AP Biology

How about large molecules?  Moving large molecules into & out of cell  through vesicles & vacuoles  endocytosis  phagocytosis = “cellular eating”  pinocytosis = “cellular drinking”  exocytosis exocytosis

AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal