Diffusion, Osmosis, and Osmoregulation NOTES January 23, DIFFUSION, OSMOSIS, and OSMOREGULATION

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1 DIFFUSION, OSMOSIS, and OSMOREGULATION

2 DIFFUSION * All molecules are in constant random motion (Brownian Motion). * The rate of this motion increases with increasing temperature and decreases with decreasing temperature. * Diffusion - the directional movement of molecules from and area of high concentration of that molecule to an area of lower concentration of that molecule. * Molecules moving from high to low concentration are said to be moving "with the concentration gradient". * No energy is required. * Diffusion occurs in the air and in water.

3 * A specialized type of diffusion. OSMOSIS Osmosis - the diffusion of water through a membrane. * No energy is required * In Biology, osmosis will always deal with the movement of water into cells or out of cells. = water molecule

4 What's wrong with this picture????? Jim Davis didn't study his Biology.

5 Passive vs. Active Transport Passive Transport - the movement of molecules, into or out of cells, with the concentration gradient. * No energy required by the cell. * Examples: diffusion and osmosis *Active Transport - the movement of molecules, into or out of cells, against the concentration gradient. (from low to high concentration) * This requires the cell to expend energy (ATP's). * Specialized proteins in cell membranes, called carrier proteins, pump the molecules against the concentration gradient. PASSIVE TRANSPORT ACTIVE TRANSPORT

6 * All cells are surrounded by a cell membrane. * Composition? Movement Into/Out of Cells * Cell membranes are selectively permeable; they discriminate based on the size of the molecule. Cell's environment Cell Cell Membrane

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8 Osmoregulation * Organisms that live in water must regulate the water concentration inside their cells to maintain homeostasis. * The osmosis problem is different for fresh water and salt water organisms. Fresh water is a hypotonic solution, while salt water is a hypertonic solution. FRESH WATER FISH SALT WATER FISH

9 Different evolutionary strategies have evolved to osmoregulate. Osmoconformers: -Don't actively maintain internal salt and water balance. Their internal concentrations change as salinity changes. - Unable to control the flooding of tissues at low salinity. - Often stay in a salinity that matches body fluids. They don't expend energy to maintain levels but, if they get outside this range, they have a problem. Many conformers are found in areas of the ocean with stable salinity. - Most marine invertebrates. Ex: Starfish, Jellyfish, Squid

10 Osmoregulators: -Actively maintain internal salt and water balance regardless of external conditions. -Most marine vertebrates are osmoregulators. Ex: Tuna, Sharks, Salmon Two regulation strategies: 1. Sharks will actively maintain a high level of the solute urea, in their tissues to match the water's solute concentration. In this way, their internal solute/water concentrations match their environment's. Not many shark species in/near fresh water. The plant Dunaliella can concentrate glycerol to regulate from fresh to 9x saltier. 2. Marine fish, use active transport to move solutes out of the cells and use their kidneys to conserve water. In addition, many marine fish will drink the salt water to replace the water lost by osmosis. Some species, like salmon, are able to go from salt to fresh water.

11 In marine fish, what cells must be in direct and constant contact with the surrounding water? Ways to "shield" cells from direct contact with the watery environment: