Class 11 Biology - Cell: The Unit of Life

Activities

Activity 8.1: Observing Onion Peel Cells

Aim/Objective: To observe the basic structure of plant cells using an onion peel.

Materials Required:

• Onion
• Forceps
• Glass slide and cover slip
• Safranin or Methylene blue stain
• Water
• Microscope
• Needle

Procedure:

1. Peel a small fleshy scale from an onion.
2. Use forceps to pull a thin, transparent layer (peel) from the inner surface.
3. Place the peel in a drop of water on a glass slide. Ensure it is flat.
4. Add a drop of Safranin or Methylene blue stain to the peel.
5. Carefully place a cover slip over the peel using a needle to avoid air bubbles.
6. Observe the slide under the low power and then high power of a microscope.

Observation:

• Rectangular or brick-like cells are seen arranged in a regular pattern.
• Each cell has a distinct cell wall, a large central vacuole, and a nucleus pushed to one side.

Explanation:

• Onion peel cells are typical plant cells. The cell wall provides a rigid structure. The staining allows us to see the nucleus and the cytoplasm clearly. The regular arrangement is characteristic of epidermal tissues in plants.

Conclusion:

• Plant cells have a defined cell wall and a structured arrangement.

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Activity 8.2: Observing Human Cheek Cells

Aim/Objective: To observe the basic structure of animal cells using human cheek cells.

Materials Required:

• Clean toothpick or spatula
• Glass slide and cover slip
• Methylene blue stain
• Water
• Microscope

Procedure:

1. Gently scrape the inner side of your cheek with a clean toothpick.
2. Place the scrapings in a drop of water on a glass slide.
3. Add a drop of Methylene blue stain.
4. Place a cover slip over the slide.
5. Observe under the microscope.

Observation:

• Irregularly shaped cells are seen scattered on the slide.
• These cells have a thin cell membrane (no cell wall), a central nucleus, and cytoplasm, but no large vacuoles.

Explanation:

• Cheek cells are animal cells. Unlike plant cells, they lack a cell wall and large vacuoles, which explains their flexible, irregular shape. Methylene blue specifically stains the nucleus, making it easy to identify.

Conclusion:

• Animal cells are distinguishable from plant cells by the absence of a cell wall and their irregular shape.