Chapter 7 Osmosis lab

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Materials

• red onion • forceps • metric ruler• Scissors• paper towel• iodine solution

• microscope slide • coverslip• dissecting probe

• microscope

• 10% salt solution

• distilled water

Procedure

1. Use your fingers to separate one of the curved layers from the onion. Bend the layer until the shiny surface cracks. Look for a thin, clear layer of tissue at the place where the surface cracked. Use forceps to peel away some of the tissue. Use a scissors to cut away the tissue, if necessary.

Procedure

• 2. Place a drop of iodine stain in the center of a clean glass slide. Use the forceps to place the onion sample in the drop of iodine on the slide and to gently flatten the tissue so that no air bubbles are trapped underneath the tissue.

• 3. Place a cover slip at an angle so that one edge touches the drop of iodine solution. Use a probe to slowly lower the cover slip over the onion tissue.

Procedure

• 4. Use the space to draw the onion cells you see in the field of view. Choose one cell and label the cell wall, nucleus, and cytoplasm. The cytoplasm will be yellow. Note whether the cytoplasm completely fills the cell.

Control

• 5. Put a few drops of salt solution at one edge of the coverslip. Hold a small piece of paper towel at the other end of the coverslip to draw the salt solution underneath the coverslip.

• 6. After 3 minutes, observe the onion cells. Use the space below to draw the cells you see in the field of view. Choose one cell and label the cell wall, nucleus, and cytoplasm. Note whether there is any empty space between the cell wall and the cell membrane.

After adding salt solution

• 7. Put a few drops of distilled water at one edge of the coverslip. Hold a new piece of paper towel at the other end of the coverslip to draw the distilled water underneath the coverslip.

• 8. After 3 minutes, observe the onion cells again. Use the space below to draw the cells you see the field of view. Choose one cell and label the cell wall, nucleus, and cytoplasm. Note whether the cytoplasm completely fills the cell.

Add distilled water

• Repeat procedure using distilled water.