Observing Osmosis with Plant and Salted Water

When plant cells absorb or lose water, the water undergoes the process called osmosis. Osmosis is the type of diffusion describing the movement of water from a hypotonic (low solute concentration) environment to a hypertonic (high solute concentration) one.

The term water potential refers to the likelihood of water molecules transporting to another environment. A more dilute solution would have less water potential than that with a high solute concentration.

Water molecules move from high to low water potential. Through this process, the water molecules can transport with them the solutes in forms of molecules or ion.

In AP biology, we conducted an experiment where green beans were soaked in solutions with different salinities and the effect of osmosis on the vegetable was observed.

Three bean samples, for soaking in fresh water and salted water

By soaking the beans in different solutions, there were some physical, textural and taste changes to the beans. In the freshwater, the bean became fresher, with a little lighter skin color and slightly thicker skin. It also became a little more crunchy (however less flexible), less sweet and more watery in term of texture and taste. This might be due to the access of more water in the bean. The bean in 20g/L saltwater became darker with some lighter-colored spots. It was softer and more flexible than the one in freshwater. There was no sweetness in the beans, and it became slightly salty and a little less watery. The bean in the 40g/L saltwater has a similar quality to the one in the 20g/L saltwater solution, except it was more flexible and less watery.

As mentioned, water movement is dependent on the solute of an environment. This means that the water molecule would move to the environment with more solute. In this case, the tissue cell of the green beans contain more solute than the freshwater solution, therefore, causing the water to move into the plant cells. On the other hand, the saltwater has more solute than in the plant tissue so the water from the plant would move to the more solute environment. This instance is similar to how some organisms became dehydrated in seawater because seawater is more solute than their body.

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