Onion Root Tip Mitosis

This experiment demonstrates mitosis by preparing and observing stained onion root tip cells under a compound microscope. Students identify the stages of mitosis while understanding why onion root tips are suitable for studying active cell division.

1. Grow onion bulbs in water until new root tips develop (4–6 days).
2. Collect about 3 cm of young root tips and place them in aceto-alcohol fixative (3:1 ethanol and glacial acetic acid) for 24 hours.
3. Transfer a root tip to a clean slide and add 0.1N HCl followed by acetocarmine stain.
4. Gently heat over a burner without drying the stain.
5. Trim off less-stained portions and retain the well-stained root tip.
6. Add a drop of water and mount a coverslip.
7. Tap the coverslip gently to squash the tissue into a thin layer.
8. Place the slide under the compound microscope and observe the stages of mitosis.

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• Use prepared slides of onion root tips if time or equipment is limited.
• Compare mitosis in onion root cells with mitosis in animal cells (e.g., whitefish blastula).
• Extend the study to include meiosis for comparison.

• Handle sharp blades and scalpels carefully.
• Use stains (acetocarmine, HCl, aceto-alcohol) cautiously; they can damage skin, clothing, and surfaces.
• Heat slides gently to avoid boiling or cracking.
• Follow all lab safety rules, including wearing gloves and protective eyewear if required.

• Why is mitosis called equational division? (Daughter cells have the same chromosome number as the parent cell.)
• Why are onion root tips commonly used to study mitosis? (They have actively dividing meristematic cells and large, visible chromosomes.)
• Which stage of mitosis shows the chromosomes most distinctly? (Metaphase, because chromosomes are thick, condensed, and aligned at the equator.)
• How can colchicine affect mitosis? (It prevents spindle fiber formation, stopping cells in metaphase.)
• How do plant and animal cells differ in spindle fiber origin? (Plant cells form spindle fibers from the cytoplasm; animal cells form them from centrioles.)