The Diffusion & Osmosis of Plants in Salt Water
Diffusion is the movement of particles across a concentration gradient from an area of higher concentration to an area of lower concentration. Osmosis is the diffusion of a substance through a semipermeable membrane from a dilute solution to a more concentrated solution. Both diffusion and osmosis are types of passive transport; they don't need outside energy to move the particles.
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Salt "Sucks"
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Salt is a solute, meaning it is a component of a solution that is dissolved. For example, when you add sugar to water, sugar is the solute and water is the solvent. When salt is concentrated on either side of the cell, it draws or sucks the water in its direction. This is why you become thirsty after consuming a salty food.
Isotonic
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If a plant is in regular salt water with an equal amount of salt and water in the solution, then the diffusion and osmosis that occurs results in an equal amount of the solute (water) on either side of the membrane. This is called isotonic. A plant cell in this type of solution neither gains nor loses water.
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Hypertonic
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However, if the plant is in a very salty water, then the plant cells experience being in a hypertonic solution. Cells in this type of solution lose water and therefore shrink and shrivel, and they eventually die. However, plants that are typically found in salt water environments undergo plasmolysis. According to Dr. Michael Gregory, biology professor at Clinton Community College in New York, plasmolysis is "a condition where the plasma membrane pulls away from the cell wall as the cell shrinks." The cell wall becomes rigid and prevents itself from shrinking. Subsequently, the plant cell doesn't die from being in a hypertonic solution.
Hypotonic
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Typically, when a cell is placed in a hypotonic solution, it swells and possibly bursts due to the overwhelming amount of water it gains. This can happen in animal cells, but the contractile vacuoles can pump water out of the cell to prevent that from occurring, thus maintaining an equilibrium. In plant cells, the cell wall itself prevents the plant from bursting because the central vacuole fills, making the plant rigid.
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