Edexcel A Level (IAL) Biology -3.15 Core Practical 6: Observing the Stages of Mitosis- Study Notes- New Syllabus

CORE PRACTICAL 6 – Root Tip Squash (Observing Mitosis)

🌱 Introduction

Mitosis = division of nucleus to produce 2 genetically identical daughter cells.
Root tips (onion, garlic) are ideal → meristematic zones = actively dividing.
This practical allows observation of all mitotic stages under a light microscope.

Aim

Prepare a root tip squash and observe mitosis under a microscope.

Materials Needed

• Fresh root tips (onion, garlic)
• Microscope slides & cover slips
• Acetic acid or HCl (softening)
• Stains: Aceto-orcein or Feulgen (chromosomes)
• Forceps, scissors
• Light microscope
• Filter paper, watch glass

Method (Step-by-Step)

1. Collect root tips: Young, actively growing (~1-2 cm).
2. Fix tips: Optional ethanol/acetic acid to preserve cells.
3. Hydrolyse / soften: 1 M HCl at 60°C for 5-10 min → softens tissue.
4. Staining: Wash, then immerse in aceto-orcein (5-10 min) or Feulgen.
5. Prepare squash: Place tip on slide, cover gently, press to spread cells into single layer.
6. Observation: Low power (×10) → locate meristematic cells. High power (×40/×100) → identify mitotic stages.

Tips for Observation

• Cells at root tip divide fastest → most mitotic cells visible.
• Prophase → chromosomes condense, nuclear membrane disappears.
• Metaphase → chromosomes align at equator.
• Anaphase → sister chromatids pulled to opposite poles.
• Telophase → chromosomes decondense, nuclear membrane reforms.
• Squash gently → prevents crushing chromosomes beyond recognition.

📊 5️⃣ Summary Table of Mitotic Stages (Root Tip Cells)

⚡ Quick Recap
Root tip squash → ideal for observing mitosis.
Stains highlight chromosomes for visibility.
Stages: Prophase → Metaphase → Anaphase → Telophase.
Gentle squash preserves structure for clear observation.
Meristematic region → high proportion of dividing cells.