Edexcel A Level (IAL) Biology -4.6 Core Practical 7: Identifying Tissue Types Within Stems- Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -4.6 Core Practical 7: Identifying Tissue Types Within Stems- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -4.6 Core Practical 7: Identifying Tissue Types Within Stems- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
- 4.6 Use a light microscope to:
(i) make observations, draw and label plan diagrams of transverse sections of roots, stems and leaves
(ii) make observations, draw and label cells of plant tissues
(iii) identify sclerenchyma fibres, phloem, sieve tubes and xylem vessels and their location.
Core Practical 7: Identifying Tissue Types Within Stems
🌱 Aim:
To use a light microscope to:
- Observe and draw plan diagrams of transverse sections (T.S.) of roots, stems, and leaves.
- Observe and draw individual cells from plant tissues.
- Identify and label sclerenchyma fibres, phloem, sieve tubes, and xylem vessels, noting their positions in each organ.
🔬 Apparatus & Materials:
- Light microscope
- Prepared T.S. slides of root, stem, and leaf
- Mounted needle, forceps, coverslip
- Microscope graticule (for measurements, if needed)
- Drawing instruments
🧩 (i) Plan Diagrams – Transverse Sections (T.S.)
1. Root (T.S.) 
Observation:
- Circular arrangement of tissues.
- Xylem forms a central star-shaped pattern with phloem between arms.
- Endodermis forms a ring around vascular bundle.
- Cortex surrounds the endodermis.
Key Labels: Xylem (center star), Phloem (between xylem arms), Endodermis, Cortex, Epidermis
🧠 Tip: Root xylem → “X” shape (X for Xylem → Root)
2. Stem (T.S.)
Observation:
- Epidermis forms outer boundary.
- Vascular bundles arranged in a ring around the central pith.
- Each vascular bundle has: Xylem (inner side), Phloem (outer side), and Sclerenchyma cap (outermost).
- Cortex lies between epidermis and vascular ring.
Key Labels: Xylem vessels, Phloem tissue, Sclerenchyma cap, Cortex, Epidermis, Pith
🧠 Tip: From inside → out = Xylem → Phloem → Sclerenchyma
3. Leaf (T.S.)
Observation:
- Upper & lower epidermis with a waxy cuticle.
Mesophyll divided into:- Palisade layer (densely packed cells → photosynthesis)
- Spongy layer (loose cells with air spaces)
- Vascular bundle (vein): Xylem on top, Phloem below.
- Stomata on lower surface.
Key Labels: Upper & lower epidermis, Palisade mesophyll, Spongy mesophyll, Xylem (above), Phloem (below), Stomata
🧠 Tip: “Xy up, Phlo down” in leaf veins (Xylem above Phloem)
🧫 (ii) Observation of Individual Cells in Plant Tissues
| Tissue | Cell Features Under Microscope | Notes |
|---|---|---|
| Parenchyma | Thin walls, living cells, large vacuoles | Storage & support |
| Collenchyma | Uneven thickening at corners | Flexible support (especially in young stems) |
| Sclerenchyma | Thick, lignified walls, no cytoplasm | Dead, mechanical support |
| Xylem vessels | Empty, thick walls, circular or polygonal | Water transport |
| Phloem sieve tubes | Living cells, sieve plates visible | Transport of sugars |
🧬 (iii) Identification of Major Tissues
| Tissue | Appearance Under Microscope | Position in Organ | Function |
|---|---|---|---|
| Sclerenchyma fibres | Long, narrow, thick lignified walls | Around vascular bundles (outermost) | Mechanical support |
| Phloem (sieve tubes + companion cells) | Thin-walled, living, often greenish | Just outside xylem | Translocation of sugars |
| Xylem vessels | Large, empty circles or ovals, thick lignified walls | Innermost part of vascular bundle | Water & mineral transport |
| Parenchyma | Thin walls, large vacuole | Cortex or pith | Storage, support, photosynthesis |
⚡ Quick Recap
Sclerenchyma → Dead, lignified → support
Xylem → Dead, lignified → water & mineral transport + support
Phloem → Living → sugar transport
Position (in stem): Xylem inside → Phloem → Sclerenchyma outside
In leaf vein: Xylem above, Phloem below
In root: Xylem star shape at center