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IB Biology HL B3.1.10 Stomatal Density Questions

Explore how stomatal counts per unit area and cobalt-chloride indicators reveal leaf-surface differences in gas exchange and water loss in IB Biology HL B3.1.10.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Compare stomatal density between upper and lower leaf epidermis using counts per unit area and leaf-adaptation evidence.
  • Use cobalt-chloride indicator patterns to identify the leaf surface with greater water loss and relate this to stomatal distribution.

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Study B3.1.10—Stomatal density conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Biology HL B3.1.10 Stomatal Density Questions question 1

[Maximum number: 1]

The stomatal density is the number of stomata per area of leaf epidermis. A study was done on the stomatal density of the lower epidermis of leaves from Protium decandrum, a tree found in the Amazon forest.

The image shows the epidermis stripped from the lower surface of a leaf.

Figure for Question IB Biology HL B3.1.10 Stomatal Density Questions question 1 — IB Biology HL

The mean stomatal density for the lower epidermis of P. decandrum was around 600 per mm2\mathrm{mm}^{2}. Predict how the stomatal density for the upper epidermis would compare.

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