P15 OSMOSIS IN THE ONION

OBJECTIVE 

The aim of this practice is to observe the process of osmosis in the onion, as well as to see the plasmolysis and the turgor  of the plant cell in each case using salt and distilled water.

MATERIAL 

• Optical microscope 
• A slide and a cover slide
• Forceps
• A dropper  
• An onion 
• A knife 
• Distilled water
• Salt
• A  100mL beaker

PROCEDURE 

Peel the onion and cut two small pieces of the inside.

Prepare two optical microscopes.

Prepare a beaker with water and salt.

Make a sample with one of the pieces and add a few drops of salt water with the help of a dropper.

Cover it with the slide and coverslip, and watch it. In this case it is not necessary to dye it.

Then prepare another sample but this time adding drops of distilled water.

Cover and observe under a microscope.

RESULTS

The sample with salt is called hypertonic solution, so the cells are going to lose water and became smaller and tighter.

The sample with distilled water is an isotonic solution, so the cells are going to absorb water and became bigger and fatter. 

QUESTIONS 

   1. When the salt solution was added to the onion cells where was the greater concentration of water? The higher concentration of water will be outside of the cell, because of the hypertonic solution, the water will go outside to equal the concentration.

   2. Which kind of transport does water follow across the membrane? Active transport by simple diffusion.