Turgescência e plasmólise

Summary

This experiment involves observing onion cells under a microscope in various solutions. Initially placed in distilled water, a hypotonic solution, the cells become turgid as water enters and fills the vacuole. When the medium is changed to a hypertonic saline solution, plasmolysis occurs as water leaves the cells, causing them to shrink. Switching back to distilled water restores turgidity as water re-enters the cells. This process highlights osmosis, the movement of water from areas of low to high solute concentration, and the role of the rigid cell wall in preventing cell lysis.

Takeaways

• 😀 The experiment involved preparing red onion epithelium in distilled water and observing it under 400x magnification.
• 😀 The distilled water acted as a hypotonic solution, causing water to enter the cells.
• 😀 As water entered the cells, the vacuoles filled up, pushing the organelles toward the cell wall, making the cells turgid.
• 😀 The turgidity of the cells was due to the water entering from the hypotonic solution into the hypertonic cell environment.
• 😀 After the cells were turgid, the mounting medium was replaced with a hypertonic saline solution.
• 😀 The hypertonic saline caused water to leave the vacuoles, leading to plasmolysis as the cell content contracted away from the cell wall.
• 😀 Plasmolysis occurred when the water left the vacuoles and the cell content shrank.
• 😀 The next step involved replacing the hypertonic solution with a hypotonic one (distilled water).
• 😀 Once again, water from the outside moved into the cell, causing the vacuoles to fill up and restore turgidity.
• 😀 The process showed that cells cannot undergo lysis due to the rigid cell wall preventing over-expansion of the vacuoles.

Q & A

What is the purpose of the experiment described in the transcript?

The purpose of the experiment is to observe how onion cells react to different tonicities of solutions, specifically focusing on the effects of distilled water (hypotonic solution) and saline solution (hypertonic solution) on cell structure and function.

What happens to onion cells when they are placed in distilled water?

When onion cells are placed in distilled water, they become turgid. This occurs because distilled water is hypotonic, causing water to enter the cell, filling the vacuoles and pushing the organelles against the cell wall.

Why do the onion cells become turgid in distilled water?

The onion cells become turgid in distilled water because the water is hypotonic, meaning it has a lower concentration of solutes than the cell's interior. Water moves into the cell by osmosis, filling the vacuole and pushing the organelles towards the cell wall.

What is plasmolysis, and how does it occur in onion cells?

Plasmolysis is the process where the cell membrane pulls away from the cell wall due to the loss of water from the vacuoles. It occurs when onion cells are placed in a hypertonic solution, like saline, which causes water to leave the cell, resulting in the shrinking of the vacuole and the retreat of the cell contents.

What happens to the onion cells when placed in a saline (hypertonic) solution?

When placed in a saline solution, which is hypertonic relative to the cell's content, water leaves the onion cells. This causes the vacuoles to shrink, and the contents of the cell pull away from the cell wall, leading to plasmolysis.

How does a hypertonic solution affect the vacuole in onion cells?

In a hypertonic solution, the vacuole shrinks as water moves out of the cell into the surrounding solution, causing the cell's contents to contract and potentially pull away from the cell wall.

What happens when the medium is changed from a hypertonic to a hypotonic solution?

When the medium is changed from a hypertonic to a hypotonic solution, such as distilled water, the water re-enters the cell, causing the vacuole to fill again, and the cell becomes turgid once more.

What role does the cell wall play in preventing cell lysis?

The cell wall plays a critical role in preventing cell lysis by providing structural support. While the vacuole fills with water in a hypotonic solution, the rigid cell wall prevents the cell from bursting, thus maintaining cell integrity.

Why doesn't the onion cell continue to expand after becoming turgid in distilled water?

The onion cell doesn't continue to expand after becoming turgid because the cell wall acts as a rigid barrier, preventing further expansion and ensuring the cell does not undergo lysis despite the increased internal pressure.

What does the experiment illustrate about osmosis in plant cells?

The experiment illustrates the principles of osmosis in plant cells, showing how water moves between the cell and its environment depending on the tonicity of the surrounding solution. It demonstrates how cells respond to hypotonic and hypertonic conditions through processes like turgor and plasmolysis.