CIE iGCSE Biology-8.1 Xylem and phloem- Study Notes- New Syllabus
CIE iGCSE Biology-8.1 Xylem and phloem- Study Notes – New syllabus
CIE iGCSE Biology-8.1 Xylem and phloem- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- State the functions of xylem and phloem:
(a) xylem – transport of water and mineral ions, and support
(b) phloem – transport of sucrose and amino acids - Identify in diagrams and images the position of xylem and phloem as seen in sections of roots, stems and leaves of non-woody dicotyledonous plants
Supplement
- Relate the structure of xylem vessels to their function, limited to:
(a) thick walls with lignin (details of lignification are not required)
(b) no cell contents
(c) cells joined end to end with no cross walls to form a long continuous tube
Functions of Xylem and Phloem in Plants
Plants have two main types of transport tissues: xylem and phloem. They help in moving water, minerals, and food substances throughout the plant.
Xylem
📌 Function:
- Transport of Water: Carries water from roots to the leaves. Water is absorbed by root hairs and moves upward through the stem.
- Transport of Mineral Ions: Dissolved minerals like nitrates and magnesium are also transported from roots to the rest of the plant.
- Support: Xylem walls contain lignin, providing strength to support the plant upright.
🧪 Key Features:
• Made of dead cells
• Long, hollow tubes with no end walls (continuous pipes)
• One-way transport (roots → leaves)
Phloem
📌 Function:
- Transport of Sucrose: Produced in leaves by photosynthesis, then transported to growing regions and storage organs.
- Transport of Amino Acids: Essential for protein synthesis in growing parts.
🔁 Direction of Transport: Movement occurs in both directions (up and down), called translocation.
🧪 Key Features:
• Made of living cells
• Contains sieve tubes and companion cells
• Companion cells provide energy for transport
📊 Summary Table:
| Tissue | Transports | Direction | Cells Alive? | Additional Function |
|---|---|---|---|---|
| Xylem | Water & mineral ions | Upward only | Dead | Structural support |
| Phloem | Sucrose & amino acids | Both directions | Living | Feeding growing/storage parts |
Positions of Xylem and Phloem in Dicot Plants
Dicotyledonous (dicot) plants show a distinct arrangement of xylem and phloem in the root, stem, and leaf. You should be able to identify their positions in cross-section diagrams.
🌱 1. ROOT (Dicot Root – Cross Section) 
Arrangement:
- Xylem is arranged in an X-shaped pattern in the center of the root.
- Phloem is found between the arms of the ‘X’.
🧪 Identifying Tip:
• No central pith in dicot roots.
• Xylem is central and star-like.
• Phloem clusters sit in between the xylem arms.
🌿 2. STEM (Dicot Stem – Cross Section)
Arrangement:
- Xylem and phloem are arranged in vascular bundles forming a ring near the outer edge.
- Xylem is on the inner side of each bundle (toward the center).
- Phloem is on the outer side (toward the epidermis).
🧪 Identifying Tip:
• Vascular bundles arranged in a circular ring.
• May see cambium (a thin layer) between xylem and phloem.
🍃 3. LEAF (Dicot Leaf – Cross Section)
Arrangement:
- Vascular bundle (midrib) is found in the center of the leaf.
- Xylem is on the upper side (toward the upper epidermis).
- Phloem is on the lower side (toward the lower epidermis).
🧪 Identifying Tip:
• Look for the midrib/vein – xylem is usually on top, phloem below.
• Found near palisade and spongy mesophyll layers.
📊 Summary Table:
| Plant Organ | Xylem Position | Phloem Position |
|---|---|---|
| Root | Central, X-shaped | Between arms of the ‘X’ |
| Stem | Inside of vascular bundle ring | Outside of vascular bundle ring |
| Leaf | Upper part of vascular bundle | Lower part of vascular bundle |
Structure of Xylem Vessels and Their Functions
🔍 What is Xylem?
Xylem is a vascular tissue in plants that:
- Transports water and mineral ions from the roots to the leaves
- Provides structural support to the plant
🧱 Structure of Xylem Vessels and How Each Feature Helps
| Structural Feature | Description | Adaptation / Function |
|---|---|---|
| 1. Long Tubular Cells | Tube-like vessel elements joined end-to-end | Forms continuous pipelines for water flow |
| 2. No Cytoplasm or Nucleus | Mature xylem cells are dead and hollow | Less resistance, more space for water movement |
| 3. No Cross Walls | End walls are broken or missing | Allows free, upward flow of water |
| 4. Thick Cell Walls | Strengthened with lignin (woody material) | Prevents collapse under pressure |
| 5. Lignified Walls | Lignin arranged in spirals or rings | Waterproofs the vessel, adds flexibility and support |
| 6. Pits | Small pores without lignin in some cells | Allows sideways water movement to adjacent tissues |
🧪 Summary of Xylem Functions
Water Transport: Moves water and minerals from root to leaves via transpiration pull and root pressure.
One-way Flow: Water only moves upward – no backward flow.
Support: Lignified cell walls give mechanical strength to the plant.
💡 Fun Analogy
Think of xylem like old-fashioned plumbing pipes:
- Long and hollow with no blockages
- No moving parts — just smooth water flow
- Rigid walls to withstand high pressure