Notes for B3.1.8 Distribution of tissues in a leaf - IB | RevisionDojo
B3.1.8 Distribution of tissues in a leaf Notes
Written by official IB examiners
Drawing a Plan Diagram of a Dicotyledonous Leaf
A plan diagram is a simplified representation of a leaf’s transverse section, focusing on the arrangement of tissues rather than individual cells.
To create a plan diagram:
Outline the Leaf: Draw a rectangle to represent the transverse section.
Label the Layers: Divide the rectangle into sections for the upper epidermis, palisade mesophyll, spongy mesophyll, vascular bundles, and lower epidermis.
Add Key Features:
Represent the waxy cuticle as a thin line at the top.
Draw stomata as small ovals or circles in the lower epidermis.
Place vascular bundles within the spongy mesophyll, labeling the xylem and phloem.
Tip
Use a ruler for straight lines and label each layer clearly. Remember, plan diagrams emphasize tissue distribution, not cellular details.
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What is a plan diagram?
Lesson
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9 minute activity
A dicot leaf is organized in layers. In a transverse section (a cut straight across the leaf), you can see where each tissue sits and link that position to its function. This layout helps the leaf capture light efficiently, exchange gases for photosynthesis, and control water loss.
Key tissues you should recognize in a dicot leaf cross-section:
Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll (with air spaces)
Vascular bundles (xylem + phloem)
Lower epidermis (with stomata and guard cells)
Definitiontransverse sectionA cross-section made by cutting across an organ at right angles to its long axis.
Analogy
A leaf is like a factory building: the roof (cuticle/upper epidermis) protects, the main work floor (palisade) captures light, open corridors (spongy mesophyll air spaces) move gases, and pipes (xylem/phloem) deliver supplies and take products away.
Common Mistake
Mixing up where most stomata are found: in many dicot leaves they are mainly in the lower epidermis (reduces water loss).
