3.2.7Unit 3: Practical Skills in Biology I
Core Practical 6: Observing the Stages of Mitosis — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 21 of 27 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4Why Root Tips
Plants grow only at specific regions called meristems, which contain many dividing cells.
Why Root Tips
Root tip meristem
- Root tip meristem Located just behind the protective root cap, this zone of cell division contains many cells in mitosis at any moment.
Suitable material
- Suitable material Garlic or onion roots are commonly used because the bulbs can be encouraged to grow roots over water in a week or two.
Squash technique
- Squash technique Staining and gently squashing the tip spreads the cells into a thin layer so single cells can be seen clearly.
Pre-prepared slides
- Pre-prepared slides Ready-made slides of root tips can be used instead when time is limited or fresh material is unavailable.
Section 2 of 4Method
Follow the steps in order and keep the acid handling safe.
1
Warm a boiling tube of 1 M hydrochloric acid in a water bath at about 60 °C for several minutes before use.
2
Cut roughly 1 cm from the root tips and leave them in the warm acid for about 5 minutes to separate and soften the cells.
3
Rinse the tips in cold water, blot them dry, and cut about 2 mm from the very end onto a microscope slide.
4
Add a drop of stain such as acetic orcein, which stains chromosomes a deep purple, and lower on a cover slip.
5
Gently squash the root tip under the cover slip, using a blunt tool or a rolling pressure, without sliding the cover slip sideways.
6
Examine the slide under the microscope, starting at low power, and draw cells showing different stages with labelled annotations.
Section 3 of 4Results and Safety
Prophase cells
- Prophase cells Chromosomes appear as dark condensed threads or rods scattered through the cell, with no clear nuclear outline.
Metaphase cells
- Metaphase cells Chromosomes form a dark line across the middle of the cell, along the equator.
Anaphase cells
- Anaphase cells Two sets of chromatids are seen moving apart towards opposite ends of the cell, often V-shaped.
Safety
- Safety Hydrochloric acid and stains are hazardous, so wear eye protection and gloves, and keep warm acid away from skin.
Section 4 of 4Exam Checklist & Tips
3.2.7 – Key Points for the Exam
- Meristem A region of plant tissue where cells divide by mitosis and growth occurs.
- Squash A preparation in which stained tissue is pressed flat to form a single layer of cells.
- Acetic orcein A stain that colours chromosomes deep purple or red.
- Root cap A layer of cells protecting the growing tip of a root.
Common Mistakes
- Taking the sample from the root cap or from far behind the tip, where very few cells are dividing.
- Sliding the cover slip sideways when squashing, which smears and damages the cells.
- Drawing cells with shaded areas or without labels, when drawings should be clear line drawings with annotations.
- Skipping the acid step, which means the cells do not separate and the squash stays thick.
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