Table of Contents
1.1 Defining the problem
Have you ever accidentally cooked a solanum tuberosum (potato) in high sodium chloride (salt) concentrated water? What was the result? This experiment is to consider how salinity influences osmosis in potato cells. By changing the concentration of salt (0%, 0.2%, 0.4%, 0.6%, 0.8%) within the water, the weight of the potato cube will be lighter or heavier than its original weight because water will exit or enter the cell due to osmosis.
The hypothesis for this experiment is that as the concentration of the salt increases, the mass of the potato decreases. According to the osmosis theory, when a plant cell is placed in a high concentrated salt solution, the mass will decrease because the potato is less concentrated than the salt solution and the water will move through the membrane of the cell and into the stronger solution. But my prediction is that for the control experiment, the mass of the potato will increase as the pure water has a weaker concentration than the potatoes and thus the water molecules will enter the cell making it heavier.
As explained earlier, osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. (1997 – 2000, Purchon)A semi-permeable membrane refers to a very thin layer of material, also known as a membrane, which allows some substances through its membrane but doesn’t allow other substances. (May 2009, Biology-online)The substances which can’t go through the membrane are molecules such as sucrose and protein. This is because they are just too large to fit through the membrane. (1997 – 2000, Purchon)A high water concentration can also be called a low chemical concentration. This means that it is a very dilute solution. A low water concentration refers to the opposite, it is a concentrated solution. (1999 – 2010, Wisc-online)
When a plant cell is put into salt water, one of three things will occur. If the medium is hypotonic, the cell will gain water through osmosis. This occurs when the solution surrounding the cell has a high water concentration. (2010, Wikipedia) The second scenario is if the medium is isotonic. This is when the solution has the same water concentration as the cell. As a result, the cell will not gain or lose water. (1999, Brown)But if the medium is hypertonic, the cell will lose water through osmosis. This happens when the water concentration surrounding the cell is low. This effect causes the cell to lose all its water resulting in the whole organism’s death. (2006, McGraw-Hill Higher Education)
Effect of Salinity on Potato Cells
High salinity causes plants to lose water through osmosis. (November 2009, Wikibooks)A potato is a plant meaning that it is made up of plant cells. A plant cell has a strong cell wall keeping the shape of the plant rigid. When the cell takes in water through osmosis, they start to swell, but the cell wall prevents them from bursting. (2010, Kimball)When potato cells are put in high water concentration, it becomes turgid. This term means swollen and hard. Inside the cell, the pressure rises and eventually the pressure reaches its limit and no more water can enter the cell. A plant must be turgid in order to be strong and healthy. (2001, Thinkquest)When potato cells, and other plant cells, are placed in concentrated salt solutions, they will lose water by osmosis, and eventually become flaccid. This term means dehydrated and soft, thus the opposite of turgid. When osmosis is viewed under a microscope, when the cell is flaccid the contents of the cells have shrunk and pulled and pulled away from the cell wall. The opposite was viewed when the cell was turgid. (Montessori Muddle, 2010)