The big idea: In a dicot root all the vascular tissue is in one central stele: a star of xylem with phloem between its arms, inside a wide cortex.
| Tissue | Where | Main function |
|---|---|---|
| Epidermis | Outer layer, with root hairs | Absorbs water and mineral ions |
| Cortex | Wide band inside the epidermis | Storage; water passes through it |
| Xylem | Star shape in the centre | Carries water and minerals up; lignified |
| Phloem | Between the arms of the xylem | Carries sugars (translocation of sap) |
The points to remember
- Root: vascular tissue in the centre; stem: vascular bundles in a ring.
- Lignin is found in the xylem, at the centre of the root.
- The tissue adapted for translocation of sap is the phloem.
Remember it as: Root: star in the middle. Stem: ring of bundles.
Real example: the buttercup root. Buttercup (Ranunculus) roots are the standard school slide: a wide cortex packed with starch and a small central stele with a clear star of xylem.
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Drawing it: Draw the root as outlines, in proportion: a thin epidermis, a wide cortex, a small central stele.
Two traps: Do not draw a ring of bundles: that is a stem. In a root the vascular tissue is in the centre.
The stele is small: keep the cortex much wider than the stele.
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How it is asked: Expect a root micrograph with letters: which tissue has lignin, which carries water, which carries sap.
IB-style questionIdentify[1 mark]
The drawing shows a buttercup root in transverse section, with four tissues labelled A to D. Where is lignin found?
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See the answer broken into clear points, with guidance on how each point earns marks.