Turgid Cells
Osmosis makes plant cells swell up, if they are surrounded by weak (hypotonic) solutions. This is because the cell sap in the vacuole of the plant cell is of a high sugar concentration (low water concentration) therefore the water molecules move from the hypotonic solution into the vacuole by osmosis. Water is passing IN to the cell which makes the vacuole expand push against the cell wall. Eventually the cell will contain as much water as it can hold and becomes TURGID. The plant cell is prevented from bursting by the strong cellulose cell wall which resists over expansion due to excess entry of water from dilute solutions. If a plant cell is turgid it provides support for the plant, and is useful in the opening of stomatal guard cells during the process of transpiration.
Flaccid Cells
If a plant does not get enough water either because the plant is losing more water through transpiration than it is taking in through osmosis, or because the plant is losing water through osmosis, then the plant will begin to wilt. This stage is when the plant becomes FLACCID. If a plant cell is placed in a strong solution (low water concentration) then the water molecules will move from the cell vacuole which has a higher water concentration into the surrounding solution. The water is therefore passing OUT of the cell which makes the vacuole shrink. This leaves the cell limp and is known as being flaccid. However if a plant contains flaccid cells is wilting, it does not mean it is dead.
Plasmolysis
This is an extreme state when plant cells are placed in very strong sugar or salt solutions. Water passes out of the cells by osmosis, as the vacuole containing the cell sap in the cell, is of a higher water concentration than the surrounding solution. The water passes OUT of the cell and the sap vacuole shrinks, making the cell flaccid. If the plant does not take in any more water, then the process continues, with more water leaving the cell. The cytoplasm begins to peel away from the cell wall and the cell becomes PLASMOLYSED. In nature, this is a rare occurrence, but is a common feature during experiments. Usually it results in the death of the cell.
Potato Tissue
Potatoes are made up of a bulky tissue structure. Similar to other plants, potato plants make glucose by the process of photosynthesis. This glucose is stored as starch in the stems and leaves, so it can be used when photosynthesis is not occurring. Glucose is stored as starch, as it does not bloat the storage cells as glucose would do due to osmosis. In particular the potato plant stores a large quantity of starch in its roots during the winter so that the plant can grow from the stored starch the following year. Humans eat this swollen root, and it is the root that we shall be using in our experiment.
Sources I used:
- The Revision Guide
- Biology for You
The Usbourne Illustrated Dictionary of Science
