Coastal Osmosis. Grade Level: 3 rd. GA Performance Standards: S3L1

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1 Coastal Osmosis Grade Level: 3 rd GA Performance Standards: S3L1 Focus Questions: What happens when a saltwater fish goes up the creek? What is osmoregulation? Objectives: The students will: Investigate how changes in the concentration of salts in water affect the water/salt balance in living cells. Identify what adaptations are necessary for an organism to live in the fluctuating salinity of the estuarine environment. Materials: Fresh potato (cut into French fry type slices) Salt Two glasses (glass, paper or foam) Water Knife Key Words: osmosis, osmoregulation, permeability, water balance Background Information: Osmosis is the flow of water through a semi-permeable membrane (membranes that are permeable to some substances but not to others) from high to low concentrations of water (Figure 1). Cell membranes in living organisms are semi-permeable, allowing water to diffuse in and out of cells but not salts. Thus, marine fish with body fluids containing lower concentrations of water than the seawater surrounding them constantly lose water through cell membranes into the water surrounding the fish (Figure 2). Freshwater fish with body fluid water concentrations higher than the freshwater of lakes or streams will gain water, which permeates through the cell walls. Both tendencies must be countered to preserve body fluid. Plants and animals preserve body fluid balance through the process of osmoregulation.

2 Figure 1. Osmosis: the diffusion of fluids through a membrane until equally concentrated. Figure 2. Fish must osmoregulate differently depending on whether they are adapted to life in fresh or salt water. Marine

3 bony (mackerel, marlin) and cartilaginous fish (sharks) lose water through gills and mouth and would become dehydrated except for adaptations designed to restrict water loss. These adaptations include taking in seawater and being able to excrete excess salt through the gills to offset the loss and conserving water a producing a very concentrated as urine using an elaborate kidney system. Freshwater fish, on the other hand, do not drink large quantities of water and do excrete copious amounts of dilute urine. Estuarine fish must be able to adjust their water balance (osmoregulate). The adaptability of marine fish is largely dependent on low permeability of their body surfaces to water (thick scales and mucous membrane) and extraordinary salt regulating activities of gills and kidneys. Teacher Preparation: (There are several experiments to demonstrate this phenomenon. This one is the easiest.) 1. Peel and slice a fresh potato 2. Each team of students should have two glasses or containers one filled with fresh water (tap water is fine) and the other filled with salty water (about1-2 tablespoons, stirred until the salt is dissolved). 3. Each team should have about 4-8 slices of potato Student Procedure: 1. Place half the potato slices in a glass with tap water and the other half in a glass with salty water. 2. Feel the potatoes at the start and record what you observe. 3. After minutes or more, feel the potatoes in each glass and record what you observe. Observations: 1. What happened to the potato slices left in the fresh water? Relate this result to a marine fish being dropped into fresh water, what would happen to it? 2. What happens to the potato slices left in the salty water? Relate this result to a fresh water fish dropped into the ocean. 3. Based on your observations, diagram or describe the flow of water between the potato plant cells and the water in each of the two environments.

4 Conclusion: Explain how changes in the concentration of water affect the water balance in living cells of estuarine animals or plants. What adaptations do animals and plants that live in estuaries need? Source: Adapted by Margaret Olsen from an existing activity from Unit Three; Coastal Ecology; North Carolina Marine Education Manual by Lundie Mauldin (Spence) and D. Frankenberg

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