Watch the video, then describe what is happening using the terms from class: hypertonic, isotonic, hypotonic, solute concentration OR concentration gradient, diffusion/osmosis, plasmolysis, flaccid, and turgid/turgor pressure.
Red Onion Cell Video
Advertisement
The onion cell in this movie goes from being flaccid to turgid. When the saline solution (or the solution that caused plasmolysis) appeared in the environment of the cell, the cell’s cytoplasm retracted from the cell wall because it had to give up water from its reserves to balance out the concentrations. When the distilled water was added to the environment, the cells were hypertonic to this solution, causing the water molecules to move from the outside of the cell towards the inside of the cell, ultimately causing the cell to become turgid, which is very great for the cell. Before any of the solutions were added to the environment of the cell, I assume that it was isotonic, the concentration of water was equal on both sides of the cell wall. Water moved into and out of the cell in both circumstances due through a process called osmosis, or the diffusion of water molecules. This is what happens in every cell, except in animal cells, water flows through a membrane, not through a cell wall.
By: Krishan on 10/16/2009
at 4:04 pm
Water and other substances are always passing through the plasma membrane in order to become isotonic (water always flows from a high to a low concentration). Plant cells have cell walls which do not let them explode when too much water is absorbed; also when there is little water iniside such cells they get into a state of distention or become turgid. Shrinking from the cytoplasm away from the wall also occurs in plant cells due to the osmotic flow of water (plasmolysis). All of this states appear in the video.
By: Ingrid Z on 10/17/2009
at 4:19 pm
onions are plants, so they have water in them. when you put the onion into salt water, you are creating a hypertonic environment for it – there is more water in the onion than in the salt water, therefore there is a concentration gradient. so, water will move out of the onion by osmosis in order to establish an equilibrium – the water concentrations must be equal, or the water will travel from an area of high concentration to an area of low concentration, in order to balance the concentration gradient. when the cell shrivals it is plasmolysis
By: Andrew on 10/18/2009
at 10:54 am
When the the onion cells were in their plasmolysis state a hypertonic solution was poured onto them and caused there membreane to shrink and come together. You can see the nucleus which is really cool becuase you saw it while it was coming together. However a hypertonic solution was added when the onion cells popped back into their original shape.Before anything was added to the onion cell the cell was in a isotonic soilution and the concentration gradient was equal.
By: ashley S on 10/18/2009
at 3:05 pm
At about 13 seconds i notice the cells are taken out of what appears to be an isotonic environment into an environment in which the fluid is hypertonic to the cell; I can tell the solution change becasue the cells appear to shrivel. I also noticed a similar reaction at about 30 seconds and the solution seems to be a more drastic hypertonic solution than the previous becasue of the more drastic shrivel change. At about 50 seconds the cell seems to have went from having hypotonic, turgor pressure to being hypertonic yet again. towards the end at 1:10, the cell appeares to have gone from a hypertonic solution to a hypotonic solution because of the swell of the cell.
By: Iyabo on 10/18/2009
at 4:04 pm
In the video the cell is at a state equiliburium which is also known as isotonic. Then as the video continues the cells start to shrink and seen to lose their shape which is called plasmolysis which literally means cells shrinks. This is caused becuase the solution on the outside of the cell is greater than the solution inside the cell also known as a hypertonic sloution causing the cell top lose water. Then the cells fill back up and seem as if they were swollon from there intial state. This process is known as turgor pressure when the cell swells uo and bursts. This is because the solution on the outside is lower than that of the inside sloution which is known as a hypotonic solution allowing the cell to gain water.
By: Antonishia on 10/19/2009
at 4:51 pm
In the video the cell is at a state equiliburium which is also known as isotonic. Then as the video continues the cells start to shrink and seems to lose their shape which is called plasmolysis which literally means cells shrinks. This is caused becuase the solution on the outside of the cell is greater than the solution inside the cell also known as a hypertonic sloution causing the cell to lose water. Then the cells fill back up and seem as if they were swollon from there intial state. This process is known as turgor pressure which is when the cell swells up and bursts. This is because the solution on the outside is lower than that of the inside sloution which is known as a hypotonic solution allowing the cell to gain water.
By: Antonishia Mcray on 10/19/2009
at 4:53 pm
At first, the onion cells are isotonic and flaccid because the solution surrounding them have the same solute concentration. Later in the video, the onion cells begin to plasmolysis because they are in a new hypertonic solution. Later, a new hypotonic solution surrounds the onion cells and cells become turgid. All of this is caused by osmosis, the flow of water from a high concentration to a lower concentration.
By: Lajoura on 10/20/2009
at 7:06 pm
Onion/plant cells love and are normally hypotonic to their environment. When the salt water is poured on the onion cells, the water in the cell(hypotonic environment) moves down its concentration gradient to the extracellular environment which is the salt water that is hypertonic. As the cell loses water, the cell membrane pulls in & away from the cell wall in a process called plasmolysis. When the normal water was added back the extracellular environment was hypotonic to the cells which were hypertonic. The water moved into the cell, down its concentration gradient by osmosis. The cell then returns to either returns to hypotonic or isotonic.
By: Brandon on 10/21/2009
at 4:40 pm
. What is most likely happening in this video, is the onion cells begins to become in a hypertonic enviornment which means there is too much salt. the ratio of water to sodium is uneven, so the cell begins to shrink as shown. If it was in an isotonic enviornment then there would be an even distribution of water inside and outside the cell and it would appear as the cell stays constant instead of it showing like it is shrinking.
By: Denise p.3 on 10/21/2009
at 7:07 pm
Extra- Credit:
Mansi 7th Period AP Bio
When the video first begins, the red onion cells are in an isotonic solution; they do not undergo any changes because the solute concentration inside and outside of the cell is the same. Since the solute concentration is equal, water moves in and out of the cells but since the cells are in an isotonic solution they make the onion flaccid and flimsy. Now a hypertonic solution was added, and in just a few minutes the cells begin to shrivel up and the cell membrane recedes from the cell wall, this process is called plasmolysis. In plasmolysis, the inside of cell has a lesser solute concentration then the outside of the cell; thus causing the cell to expel out all its water making it shrivel. In this state, usually a plant just ends up dying. Near the end of the video a hypotonic solution is added, and soon the shriveled up cells begin to puff back out and the cell membrane begins to make contact with the cell wall, this is called turgor pressure. During turgor pressure, the solute concentration is greater inside the cell than the outside of the cell, this causes the cell to suck up more water which makes the cell puff and inflate. This puts pressure on the cell wall, but plants like this type of solution because this is how a plant becomes so leafy and healthy. Even though in all three solutions the end result is different, the process is quite the same. When plant cells are placed in any of these solutions they all undergo osmosis, the movement of water from high concentration to low concentration through a semi-permeable membrane. Whether the water goes inside of the cell, outside of the cell, or flows in both directions equally, it is still osmosis.
By: Mansi on 10/21/2009
at 7:19 pm