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Mitosis Practical Using Root Tips

May 22, 2025

Biology Lecture: Mitosis Root Tip Squash Practical

Overview

  • Practical involves preparing a stained squash of cells to work out the mitotic index.
  • Topics covered include equipment, method, risk assessment, calculation of mitotic index, and exam questions.

Equipment

  • Hydrochloric Acid: Used to soften root tissues.
  • Stain (Acetic Orcein): Stains chromosomes for visibility under a microscope.
  • Mounted Needle: Used to gently lower cover slip to avoid air bubbles.
  • Root Tip: Use onion or garlic root tip (last 5mm) as it is the growing region where cells are dividing (mitosis).

Method

  1. Preparation of Root Tips
    • Grow garlic/onion on water for three days to develop roots.
  2. Cutting the Root Tips
    • Use a scalpel to cut the last 5mm.
    • Ensure safety by cutting away from the body.
  3. Soften Root Tissues
    • Place root tip in hydrochloric acid and water bath at 60°C for 10 minutes.
    • Rinse with distilled water after pouring off acid.
  4. Staining and Mounting
    • Transfer root to microscope slide.
    • Add two drops of acetic orcein stain.
    • Use mounted needle to lower cover slip gently.
  5. Squashing the Slide
    • Place filter paper on top and gently press down.
    • Ensure a thin layer for light passage without breaking the cover slip.

Risk Assessment

  • Scalpel: Risk of cuts—use a white tile and cut away from body.
  • Hydrochloric Acid: Irritant or corrosive—wear goggles and wash hands if contacted.
  • Mounted Needle: Handle carefully to avoid injury.

Observations

  • Examine slides under a microscope for cells in mitosis stages like anaphase and metaphase.
  • Often few cells are clearly visible in stages of mitosis.

Calculating Mitotic Index

  • Formula: (Number of cells in mitosis / Total number of cells) Ă— 100
  • Example Calculation: If 3 out of 32 cells are in mitosis, mitotic index is 9.38%.

Exam Questions

  1. Why only use the first 5mm of root tip?
    • Region of active cell division (mitosis).
  2. Why press down firmly?
    • To create a thin layer for light passage.
  3. Why use a stain?
    • To make chromosomes visible.

Tips for Accurate Counting

  • Examine multiple fields of view to ensure representative sampling.
  • Average the mitotic index from at least 10 different fields of view.

This practical experiment is essential for understanding cell division and is a common exam topic. Ensure to follow safety guidelines and practice careful handling of equipment.

Full transcript