Osmosis is one of the most important ways that animals and plants maintain homeostasis. Keeping internal conditions stable makes it possible for living things to survive. Our Osmosis lab provides students with a visual representation to identify and quantify cell response to changes in osmotic conditions.
Students will explore osmosis while trying to explain how a bull shark, which is native to the Gulf of Mexico, could be found swimming up the Mississippi river near St. Louis. In this lab, students will learn about osmosis and osmoregulation by looking at the protozoan Tetrahymena, a model organism often used in research on health and disease related topics. Tetrahymena’s basic cell processes can serve as a model to better understand osmosis and osmoregulation.
Contractile vacuoles
The contractile vacuole is an organelle that is very important for osmoregulation in many cells, including Tetrahymena. The contractile vacuole helps to control the relative concentration of water and solutes in the cell by collecting water from within the cell (diastole stage) and periodically pumping it out into the environment by a mechanism involving membrane contraction (systole stage). The rhythmic pulsing of the contractile vacuole is easily visible under the light microscope, and the size of the contractile vacuole as well as the rate of contraction can be affected by environmental changes. This clip shows many Tetrahymena cells in which the contractile vacuoles are evident. Following the cells inside the circles will allow you to see complete contractile vacuole cycles in a live cells.
Module Protocols
Relevant Concepts
Water and Chemistry of Life; Physiological Regulation; Relationship of Structure to Function; Homeostasis; Feedback Mechanisms; Structural similarity between Single cell and Multicellular Organisms
Next Generation Science Standards Relationships
High School:
HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
HS-LS1-3 Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.
Middle School:
MS-LS1-1 Conduct an investigation to provide evidence that living things are made of cells, either one cell or many different and types of cells.
MS-LS1-2 Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.
References
●Dunham Philip B. 1964. The Adaptation of Tetrahymena to a High NaCl Environment. Biol.Bull. 126 (3):pp. 373-390.
References
●Gounaris EG, Bardopoulou H, Kotinis KK. 1990. Biochemical and physiological responses of Tetrahymena pyriformis during adaptation to high glycerol concentrations. Microbiologica 13 (3):239-246.
●Gounaris EG and Kotinis KK. 1990. Physiological response of Tetrahymena pyriformis during adaptation to elevated external salinity. Microbiologica 13 (1):73-76.
●Morrison GA and Tomkins AL. 1973. Determination of mean cell size of Tetrahymena in growing cultures. J.Gen.Microbiol. 77 (2):383-392.
●Orias E, Hamilton EP, Flacks M. 1979. Osmotic shock prevents nuclear exchange and produces whole-genome homozygotes in conjugating Tetrahymena. Science 203 (4381):660-663.
●Rifkin JL. 1973. The role of the contractile vacuole in the osmoregulation of Tetrahymena pyriformis. J.Protozool. 20 (1):108-114.
●Stoner LC and Dunham PB. 1970. Regulation of cellular osmolarity and volume in Tetrahymena. J.Exp.Biol. 53 (2):391-399.
See our glossary for the terms used in the modules.