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Understanding the physical mechanisms that underlie ocean circulation is essential to managing the incredible diversity of life that is found exclusively in marine habitats. Ocean habitats are some of the most diverse and spacious. Oceans cover 71% of the surface of the globe and comprise 50-80% of the Earth’s biota. In particular, coral reefs are biodiversity hotspots where an especially large number of species can be found; but these same species are also particularly threatened due to human activities. When biodiversity is high it can help buffer against big disturbances (such as climate change and pollution) in the future. When biodiversity is driven to low levels, it may also make these systems more susceptible to collapse.An understanding of concentration gradients is incredibly important for understanding most physical phenomena on earth: from ocean circulation, to osmosis/diffusion, electricity, plant water use, human oxygen consumption, and pest management. To learn more about the role of concentration gradients in each of these processes, read below and click the links.Ocean Circulation: Ocean circulation is driven by many things (wind, surface currents, thermohaline circulation, tides). But understanding just a small part of this process is important. Furthermore, concentration gradients in oceans are based on physical properties that can help us understand more about the physical world in general. Read more here.Osmosis: No matter how complicated it sounds in your biology textbook, osmosis is the simplest form of a concentration gradient. This is the simple movement of water molecules from a high concentration to a low concentration. But this is the special word just for water concentration gradients. Read more here.Diffusion: Similarly, diffusion is the word we give for the movement of solutes (ions, etc) from high concentrations to low concentrations (but don’t get confused, on a physical level these processes are exactly the same!). Read more here.Electricity: one side of a battery is rich in electrons, and the other side is deficient in electrons. The electrons want to move from high concentrations to low concentrations but they are separated by an impenetrable wall. They can only equilibrate when the two sides of the battery are connected by a wire forming an electronic circuit (or when a switch is flipped completing the continuity of that wire). Read more here.Water loss in plants: Plants need H2O for basic metabolic functions (photosynthesis), but they also lose water as a byproduct of photosynthesis. The leaf of a plant has tiny little pores (similar to the pores on your face) that the plant can open or close depending on the conditions of the day. A plant has to open these pores in order to conduct photosynthesis (and let CO2 in), but in the process H2O escapes. This is due to concentration gradients. The air surrounding a plant almost always has less water in it than the intracellular space inside the plant’s leaf. This creates a concentration gradient from high concentration inside the leaf to low concentration outside the leaf. When the plant opens the pores on the surface, water molecules randomly bounce out of the leaf surface and into the air. Read more here.Human lungs and oxygen: Similarly to water diffusing out of the plant, O2 is in high concentrations in the air we breathe. Conversely, O2 is in low concentrations in our blood as it enters into the area surrounding our lungs. O2 diffuses into the lungs in the alveolar air space for as long as the concentration in the air spaces around the blood is higher than the blood itself. Read more here.Pest management: hHve you ever had a friend with a garden who uses salt to control pesky slugs? The reason it works is because of concentration gradients. When you pour salt on the surface of the slug, the relative amount of water on the slug skin is lowered (because now some of that space is taken up by salt). This establishes a concentration gradient from the inside of the slug (high water) to the outside of the slug (relatively low water) that allows all of the water inside the slug to randomly bounce out. This eventually dehydrates the slug and kills it.
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TED-Ed
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The physical basis for concentration gradients is referred to as the second law of thermodynamics: all systems go from high organization to low organization over time.
02/25/2014 • 
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