Question

List the observations which you make when you view an onion peel

Answer 1

Observations

• There are a large number of regularly shaped cells lying side by side and each cell has a distinct cell wall.
• A distinct nucleus is present on the periphery of each cell.
• Lightly stained cytoplasm is observed in each cell.
• A large vacuole is present at the centre of each cell, and is surrounded by the cytoplasm.

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Answer 2

Large, rectangular interlocking cells,

Clearly visible distinct cell walls surrounding the cells,

Dark stained nucleus,

Large vacuoles at the center,

Small granules may be observed inside the cells (within the cytoplasm)

The layers of an onion contain simple sugars (carbohydrates) some of which are stored as starch (starch granules). Given that iodine tends to bind to starch, it stains the starch granules when the two come in to contact making them visible.

Although onions may not have as much starch as potato and other plants, the stain (iodine) allows for the little starch molecules to be visible under the microscope. Although onions are plants, students will not see any chloroplasts in their slides.

This is because of the fact that the chloroplast necessary for photosynthesis is largely present in the leafy part of the onion, which is exposed to the sun and absent in the bulb which is below ground and away from sunlight.

Unlike animal cells, students will also notice that the plant cells have a more regular shape. This is because they have a cell wall made up of cellulose which maintains its shape.