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Research Article| March 01 2021 Brian Rafferty, BRIAN RAFFERTY () is an Assistant Professor in the Science Department, Borough of Manhattan Community College, New York, NY 10007. Search for other works by this author on: Lalitha Jayant LALITHA JAYANT is a Professor in the Science Department, Borough of Manhattan Community College, New York, NY 10007. Search for other works by this author on: The American Biology Teacher (2021) 83 (3): 185–187.
The inability of students to properly understand the principles underlying osmosis and tonicity leads to misconceptions that further impair their ability to apply these concepts to physiological situations. We describe a simple and inexpensive visual exercise using beads and water to mimic solutions. Using these model solutions, students will understand the concepts of tonicity and
osmolarity. The hands-on exercise is supplemented with a worksheet that reinforces the concepts they learned in doing the activity. This exercise has broad application with respect to both the level of students targeted and the courses in which it can be utilized, and it is flexible enough to personalize for each situation. © 2021 by The Regents of the University of California 2021 You do not currently have access to this content. Sign inClient AccountYou could not be signed in. Please check your email address / username and password and try again. Email address / Username ? Password IntroductionIn physiology, osmosis (Greek for push) is the net movement of water across a semipermeable membrane.[1][2] Across this membrane, water will tend to move from an area of high concentration to an area of low concentration. It is important to emphasize that ideal osmosis requires only the movement of pure water across the membrane without any movement of solute particles across the semipermeable membrane. Osmosis can still occur with some permeability of solute particles, but the osmotic effect becomes reduced with greater solute permeability across the semipermeable membrane. It is also true that, at a specific moment in time, water molecules can move towards either the higher or lower concentration solutions, but the net movement of water will be towards the higher solute concentration. The compartment with the highest solute and lowest water concentration has the greatest osmotic pressure. Osmotic pressure can be calculated with the van 't Hoff equation, which states that osmotic pressure depends on the number of solute particles, temperature, and how well a solute particle can move across a membrane. Its measured osmolality can describe the osmotic pressure of a solution. The osmolality of a solution describes how many particles are dissolved in the solution. The reflection coefficient of a semipermeable membrane describes how well solutes permeate the membrane. This coefficient ranges from 0 to 1. A reflection coefficient of 1 means a solute is impermeable. A reflection coefficient of 0 means a solute can freely permeable, and the solute can no generate osmotic pressure across the membrane.[2] The compartment with the greatest osmotic pressure will pull water in and tend to equalize the solute concentration difference between the compartments. The physical driving force of osmosis is the increase in entropy generated by the movement of free water molecules. There is also thought that the interaction of solute particles with membrane pores is involved in generating a negative pressure, which is the osmotic pressure driving the flow of water.[3] Reverse osmosis occurs when water is forced to flow in the opposite direction. In reverse osmosis, water flows into the compartment with lower osmotic pressure and higher water concentration. This flow is only possible with the application of an external force to the system. Reverse osmosis is commonly used to purify drinking water and requires the input of energy. [4] The concept of osmosis should not be confused with diffusion. Diffusion is the net movement of particles from an area of high to low concentration. One can think of osmosis as a specific type of diffusion. Both osmosis and diffusion are passive processes and involve the movement of particles from an area of high to low concentration.[2][5] CellularThe rate of osmosis always depends on the concentration of solute. The process is illustrated by comparing an environmental or external solution to the internal concentration found in the body. A hypertonic solution is any external solution that has a high solute concentration and low water concentration compared to body fluids. In a hypertonic solution, the net movement of water will be out of the body and into the solution. A cell placed into a hypertonic solution will shrivel and die by a process known as plasmolysis. An isotonic solution is any external solution that has the same solute concentration and water concentration compared to body fluids. In an isotonic solution, no net movement of water will take place. A hypotonic tonic solution is any external solution that has a low solute concentration and high water concentration compared to body fluids. In hypotonic solutions, there is a net movement of water from the solution into the body. A cell placed into a hypotonic solution will swell and expand until it eventually burst through a process known as cytolysis. These three examples of different solute concentrations provide an illustration of the spectrum of water movement based on solute concentration through the process of osmosis. The body, therefore, must regulate solute concentrations to prevent cell damage and control the movement of water where needed. Summary of Red Blood Cell Placed into Hypertonic, Isotonic, and Hypotonic Solutions Hypertonic A hypertonic solution has a higher solute concentration compared to the intracellular solute concentration. When placing a red blood cell in any hypertonic solution, there will be a movement of free water out of the cell and into the solution. This movement occurs through osmosis because the cell has more free water than the solution. After the solutions are allowed to equilibrate, the result will be a cell with a lower overall volume. The remaining volume inside the cell will have a higher solute concentration, and the cell will appear shriveled under the microscope. The solution will be more dilute than originally. The overall process is known as plasmolysis. Isotonic An isotonic solution has the same solute concentration compared to the intracellular solute concentration. When a red blood cell is placed in an isotonic solution, there will be no net movement of water. Both the concentration of solute and water are equal both intracellularly and extracellularly; therefore, there will be no net movement of water towards the solution or the cell. The cell and the environment around it are in equilibrium, and the cell should remain unchanged under the microscope. Hypotonic A hypotonic solution has a lower solute concentration compared to the intracellular solute concentration. When a red blood cell is placed in a hypotonic solution, there will be a net movement of free water into the cell. This situation will result in an increased intracellular volume with a lower intracellular solute concentration. The solution will end up with a higher overall solute concentration. Under the microscope, the cell may appear engorged, and the cell membrane may eventually rupture. This overall process is known as cytolysis. Note that osmosis is a dynamic equilibrium, so at any given moment, water molecular can momentarily flow toward any direction across the semipermeable membrane, but the overall net movement of all water molecules will be from an area of high free water concentration to an area of low free water concentration.[5][6] Clinical SignificanceWater is known as the "universal solvent," and almost all known life depends on it for survival. Therefore, the principle of osmosis, though seemingly simple, plays a large role in almost all physiological processes. Osmosis is specifically important in maintaining homeostasis, which is the tendency of systems toward a relatively stable dynamic equilibrium. Biological membranes act as semipermeable barriers and allow for the process of osmosis to occur. Osmosis underlies almost all major processes in the body, including digestion, kidney function, nerve conduction, etc. It allows for water and nutrient concentrations to be at equilibrium in all of the cells of the body. It is the underlying physical process that regulates solute concentration in and out of cells, and aids in excreting excess water out of the body.[2][7][8][9][10][11]  FigureThe image shows the process of osmosis. Contributed from Cornell, B. 2016. Referencing. [ONLINE] Available at: http://ib.bioninja.com.au/standard-level/topic-1-cell-biology/14-membrane-transport/osmosis.html References1.Chen JS, Sabir S, Al Khalili Y. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): May 9, 2021. Physiology, Osmoregulation and Excretion. [PubMed: 31082152] 2.Marbach S, Bocquet L. Osmosis, from molecular insights to large-scale applications. Chem Soc Rev. 2019 Jun 04;48(11):3102-3144. [PubMed: 31114820] 3.Kiil F. Molecular mechanisms of osmosis. Am J Physiol. 1989 Apr;256(4 Pt 2):R801-8. [PubMed: 2705569] 4.Greenlee LF, Lawler DF, Freeman BD, Marrot B, Moulin P. Reverse osmosis desalination: water sources, technology, and today's challenges. Water Res. 2009 May;43(9):2317-48. [PubMed: 19371922] 5.Goodhead LK, MacMillan FM. Measuring osmosis and hemolysis of red blood cells. Adv Physiol Educ. 2017 Jun 01;41(2):298-305. [PubMed: 28526694] 6.Maldonado KA, Mohiuddin SS. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 17, 2021. Biochemistry, Hypertonicity. [PubMed: 31082139] 7.Kiil F. Mechanism of osmosis. Kidney Int. 1982 Feb;21(2):303-8. [PubMed: 7069994] 8.Meir E, Perry J, Stal D, Maruca S, Klopfer E. How effective are simulated molecular-level experiments for teaching diffusion and osmosis? Cell Biol Educ. 2005 Fall;4(3):235-48. [PMC free article: PMC1200778] [PubMed: 16220144] 9.Schultz SG. Epithelial water absorption: osmosis or cotransport? Proc Natl Acad Sci U S A. 2001 Mar 27;98(7):3628-30. [PMC free article: PMC33327] [PubMed: 11274376] 10.Ogobuiro I, Tuma F. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Jul 26, 2021. Physiology, Renal. [PubMed: 30855923] 11.Trigo D, Smith KJ. Axonal morphological changes following impulse activity in mouse peripheral nerve in vivo: the return pathway for sodium ions. J Physiol. 2015 Feb 15;593(4):987-1002. [PMC free article: PMC4398533] [PubMed: 25524071] When a cell and a solution have the same concentration of solutes that are considered?Isotonic: The solutions being compared have equal concentration of solutes. Hypertonic: The solution with the higher concentration of solutes. Hypotonic: The solution with the lower concentration of solutes.
What has the same concentration of solute and therefore water as the cell?When a red blood cell is placed in an isotonic solution, there will be no net movement of water. Both the concentration of solute and water are equal both intracellularly and extracellularly; therefore, there will be no net movement of water towards the solution or the cell.
What is a solution with equal solutes concentration and water concentration?An isotonic solution is defined as two solutions of equal concentrations of solutes and water separated by a semipermeable membrane to allow water to move freely in and out of a cell.
What do we call a solution that is the same concentration as in a cell?An isotonic solution has the same concentration of solutes both inside and outside the cell. For example, a cell with the same concentration of salt inside it as in the surrounding water/fluid would be said to be in an isotonic solution.
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When a cell is in a solution that has the same concentration of water and solute the cell is said to be in an?
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