Plasmolysis in Onion Cells

Author(s): Afrodita Fuentes
Microscopy - Teacher's Guide
SED 695B

Microscopy Equipment


Topics addressed

  • cellular structure
  • plasmolysis
  • Hypertonic solution
  • preparation of wet-mount slides
  • microscopy
  • technology

Description of Investigation

A simple microscope allows the observation of cells and many microscopic organisms and their behaviors in different environments. In this investigation, the process of plasmolysis is observed in onion cells. A hypertonic solution (salty water) to the onion tissue is placed onto it, thus forcing the water out of the cell. As the water comes out of the cell, the cell membrane detaches from the the cell wall. Other

Note: using a microscope camera is very efficient in showing students what they need to see when using their own microscope. Recording and saving images can be even more efficient, but a lot of technique is necessary.



  • red/purple onion
  • Scalpel & forceps
  • water
  • 10%-15% salty solution
  • microscope slides and microscope slips
  • microscope
  • microscope camera & software
  • computer

Study Guide:



Questions: included in study guide


Preparing a wet-mount slide of onion cells

For microscopic observation,why is it necessary to use only the thin skin of the onion cell?

Why use red/purple onion cells and not white onions?

2 Prepared wet-mount slides of onion cells

What cell parts should be identifiable under the microscope?

Osmotically Balanced Onion Cells under the Microscope

Notice the cell at the end of the pointer, its membrane is detaching from the cell wall. What could be causing this?

Osmotically Unbalanced Onion Cells under the Microscope

Plasmolysis in Onion cells. The onion cells have been exposed to a hypertonic solution (salty water). Explain what is happening at the cellular level.

References & Links: - for pond water organism identification