Lab Report: Osmosis in Onion Cells

Abstract

In this experiment, the phenomenon of osmosis in onion cells was observed by immersing them in solutions of different salt concentrations. The objective was to investigate how varying salt concentrations influence osmosis within the onion cells. The results demonstrated that osmosis caused changes in cell size and shape, providing valuable insights into the selective permeability of cell membranes.

Introduction

The movement of water molecules through a selectively permeable membrane is known as osmosis. Osmosis involves the flow of water from an area of lower solute concentration to an area of higher solute concentration.

In this experiment, we aimed to explore the effects of different salt concentrations on osmosis in onion cells. Specifically, we wanted to answer the question: How do solutions of various salt concentrations influence osmosis in relation to an onion cell?

Hypothesis

We hypothesized that when an onion cell is placed in a saltwater solution, the cell would undergo dehydration and shrink due to the higher concentration of solutes outside the cell.

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Conversely, when the onion cell is placed in distilled water, it would absorb water, causing it to swell.

Independent Variable: Salt solution and distilled water
Dependent Variable: Changes in the size and shape of the onion cell

Materials

• Microscope
• Thin onion strip
• Glass slide
• Small plastic cover slip
• Iodine stain pipette
• Tweezer
• Paper towel strip
• Small beaker
• Salt solution

Experimental Procedure

1. Carefully remove the outer layer of cells (epidermis) from a piece of red onion.
2. Place a drop of water in the center of a clean dry slide.
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3. Using tweezers, place the onion strip in the middle of the water drop.
4. Hold the cover slip upright and carefully lower one edge of the cover slip onto the water, minimizing air bubbles underneath.
5. Examine the slide under low power and sketch a drawing of the onion cells.
6. Remove the slide from the microscope stage and place it on the desktop.
7. Add several drops of salt solution to one side of the cover slip while placing a small piece of paper towel along the opposite edge of the cover slip.
8. Observe the slide to see the effects of the saline (salt) solution on the onion cells and record your observations.
9. Replace the sodium chloride solution with distilled water in the same manner as the salt solution was added.

Results

The observations made during the experiment are summarized in the table below:

Discussion

The results of this experiment support the hypothesis that the salt solution caused the onion cells to shrink, while the distilled water led to cell expansion. This can be explained by the principles of osmosis.

When the onion cells were placed in the salt solution, which had a higher solute concentration than the cell's cytoplasm, water molecules moved out of the cells through the semi-permeable cell membrane. As a result, the cells dehydrated and shrank. This observation aligns with the concept that water moves from areas of lower solute concentration to areas of higher solute concentration.

In contrast, when the onion cells were placed in distilled water, which had a lower solute concentration than the cell's cytoplasm, water moved into the cells, causing them to swell and return to their original state. The cell membrane is selectively permeable, allowing water molecules to pass through freely but restricting the passage of larger solute molecules, such as salt.

This experiment illustrates the importance of selectively permeable membranes in biological systems and the role of osmosis in maintaining cell turgidity and homeostasis. It also highlights the practical applications of osmosis in fields such as biology and agriculture, where understanding how solute concentrations affect cellular processes is crucial.

Conclusion

In conclusion, this experiment demonstrated the effects of different salt concentrations on osmosis in onion cells. The results confirmed that osmosis causes changes in cell size and shape, with cells shrinking in a hypertonic solution (salt solution) and expanding in a hypotonic solution (distilled water). This experiment provides valuable insights into the fundamental biological process of osmosis and its relevance in maintaining cellular integrity.

Recommendations

Further investigations could explore the relationship between the concentration of salt solution and the extent of cell shrinkage or expansion. Additionally, studying the impact of osmosis on various types of plant cells could yield valuable information for agricultural practices and understanding plant physiology.