4.1.6Unit 4: Energy, Environment, Microbiology and Immunity
Core Practical 7: Identifying Tissue Types Within Stems — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 13 of 28 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 4Preparing the Slide
A permanent slide can be used, or a stem section can be cut and stained.
1
Use a scalpel to cut a very thin cross-section of the stem, since thick sections block light and hide the tissues.
2
Transfer the sections into a dish of stain such as toluidine blue O and leave them for about a minute.
3
In toluidine blue O, xylem and sclerenchyma fibres stain blue-green and phloem appears pinkish purple.
4
Rinse the sections in water and mount one on a slide with forceps and a dissecting needle.
5
Lower a cover slip slowly from one side so no air bubbles are trapped, as bubbles can be mistaken for tissue.
6
View under the microscope, adjust the focus for a clear image, and make a labelled drawing of the tissue positions.
Section 2 of 4Plan Diagrams
A plan diagram shows the arrangement of tissues, not individual cells.
Size and lines
- Size and lines Draw a large diagram with a sharp pencil, clear continuous lines and no shading or sketching.
Low power
- Low power Do not draw individual cells;
- show the outlines of tissues in correct proportions and include the magnification.
High power
- High power Draw only a few cells, include the cell walls, and state the magnification used.
Proportions
- Proportions An eyepiece graticule can help keep the relative sizes of tissues accurate.
Section 3 of 4Labelling and Safety
Labelling and Safety
Label lines
- Label lines Use a ruler, make each line end exactly on the structure, avoid arrows and do not let lines cross.
Tissues to label
- Tissues to label Label xylem vessels, phloem sieve tubes and sclerenchyma fibres, and any other structures the question asks for.
Safety
- Safety Scalpels are sharp, so cut away from the body onto a tile and wear gloves when handling the stain.
Expected pattern
- Expected pattern In a stem the xylem lies inside each bundle and the phloem outside it, with sclerenchyma nearby.
Section 4 of 4Exam Checklist & Tips
4.1.6 – Key Points for the Exam
- Cross-section A thin slice cut at right angles to the length of the stem.
- Plan diagram A drawing showing the arrangement of tissues without individual cells.
- Toluidine blue O A stain that colours xylem and sclerenchyma blue-green and phloem pinkish purple.
- Graticule A scale in the eyepiece used to measure or compare sizes.
Common Mistakes
- Cutting thick sections, which are too opaque for the light microscope to show detail.
- Drawing individual cells in a low-power plan diagram, when only tissue boundaries are needed.
- Shading areas or using sketchy lines instead of clear continuous lines.
- Using arrowheads or crossing label lines, and not making the label line end exactly on the structure.
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