Osmosis in Onion Epidermis

Preparing a wet mount slide opens up a world of possibilities. Here, onion epidermis cells show the process of osmosis in action. Osmosis, or the net movement of water molecules from an area of high water potential to an area of low water potential, is integral to many life processes. 

The circle in each cell is the nucleus, which contains the cell DNA. 

These cells are isotonic; they are in a solution that has the same solute concentration as the inside of the cell. There is no net movement of water. 

Now, the onion epidermis has been sprinkled with salt. So, there is a greater solute concentration outside the cell compared to inside the cell. In order for the cells to achieve the same ratio of water to salt as their exterior, water leaves the cell. These causes the cells to shrivel up and become hypertonic. 

Objective: 4x (previous 4 photos)

Sometimes, water droplets look like vinyl records when making wet mounts. 

Objective: 10x (previous 4 photos)

Objective: 40x (previous photo)