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2.7.7Inquiry Process

Drawing Root and Stem Structure- Skills — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 79 of 160

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Part 1 of 4Dicot Stem

2.7.7 Drawing Root and Stem Structure- Skills

Plan diagrams show tissue layers and not individual cells.

Epidermis
  • The outer protective layer of the stem, often covered by a cuticle that reduces water loss.
Cortex
  • A layer of cells between the epidermis and the vascular tissue that gives support and stores food.
Vascular bundles
  • Bundles arranged in a ring, each with xylem on the inner side and phloem on the outer side.
Cambium
  • A thin layer of dividing cells between xylem and phloem in each bundle that produces new vascular tissue.
Pith
  • Parenchyma cells at the centre of the stem that store food.

Part 2 of 4Dicot Root

Epidermis with root hairs
  • The outer layer bears extensions that increase the area for absorbing water and minerals.
Cortex
  • Wide layer of storage cells with air spaces that water passes through on its way inwards.
Endodermis
  • A ring of cells around the vascular tissue that regulates which substances enter the xylem.
Central vascular tissue
  • Xylem forms a solid star or X shape, with phloem lying between its arms.
FeatureStemRoot
Xylem positionInner part of each bundleCentral star shape
BundlesRing near edgeCentral core
PithPresentUsually absent

Part 3 of 4Drawing Method

1
Examine the section at low power and decide the outline and the proportion of each tissue.
2
Draw the outline with a sharp pencil using continuous lines and no shading.
3
Draw the boundaries between tissues without drawing individual cells.
4
Add label lines with a ruler, from the structure to the side of the page.
5
Add a title and, if possible, the magnification or a scale bar to show size.

Part 4 of 4Exam Checklist & Tips

2.7.7 – Key Points for the Exam

  • Vascular bundle A strand of xylem and phloem running through the plant.
  • Cambium A tissue of dividing cells that produces new xylem and phloem.
  • Endodermis The inner layer of the root cortex surrounding the vascular tissue.
  • Cortex The tissue between the epidermis and the vascular tissue.

Common Mistakes

  • Drawing individual cells in a plan diagram.
  • Placing the phloem inside the xylem in a stem bundle; phloem is on the outside.
  • Giving the root a pith; dicot roots have a solid central xylem instead.
  • Forgetting to label the cambium between xylem and phloem.

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