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Difficulty: Very hardBiomes and Aquatic/Terrestrial Habitats

An ecologist analyzes plant anatomical and physiological adaptations along a south-to-north gradient across three distinct Nigerian biomes:

1. Zone I: Characterized by anaerobic muddy soil, high salinity, and regular tidal fluctuations.
2. Zone II: Characterized by heavy annual rainfall (>2,500 mm>2,500\text{ mm}), multi-layered dense canopy, high atmospheric humidity, and leached acidic topsoil.
3. Zone III: Characterized by prolonged dry seasons, high seasonal wildfire incidence, coarse sandy soil, and intense solar radiation.

Which set of structural adaptations correctly matches the dominant flora of Zone I, Zone II, and Zone III, respectively?

  1. Zone I: Pneumatophores and prop roots; Zone II: Buttress roots and drip-tip leaves; Zone III: Thick corky fire-resistant bark and underground rootstocks (lignotubers)Answer
  2. B
    Zone I: Deep taproot systems and reduced needle-like leaves; Zone II: Succulent stems and sunken stomata; Zone III: Broad papery leaves and epiphytic roots
  3. C
    Zone I: Buttress roots and broad drip-tip leaves; Zone II: Pneumatophores and salt-excreting glands; Zone III: Air bladders and floating leaf lamina
  4. D
    Zone I: Thick corky bark and lignotubers; Zone II: Deep taproots and needle-like spines; Zone III: Buttress roots and prop roots

Answer

Zone I: Pneumatophores and prop roots; Zone II: Buttress roots and drip-tip leaves; Zone III: Thick corky fire-resistant bark and underground rootstocks (lignotubers)
The correct selection accurately pairs each vegetation zone along Nigeria's south-to-north ecological gradient with its key structural adaptations: Mangrove Swamps (Zone I) feature pneumatophores and prop roots for aeration and stability; Tropical Rainforests (Zone II) feature buttress roots for structural support in leached soil and drip-tips to drain excess rainwater; Savannas (Zone III) feature fire-resistant corky bark and subterranean lignotubers for survival during seasonal droughts and bushfires.

Step-by-Step Solution

1
Identify environmental stressors for Zone I
Zone I represents the Mangrove Swamp Forest (coastal wetland), requiring specialized adaptations for anaerobic soil and salt water such as negative geotropic respiratory roots (pneumatophores), lenticels, and supportive prop roots.
Anaerobic, waterlogged mud prevents roots from obtaining oxygen for respiration unless specialized aerial root structures exist.
2
Identify environmental stressors for Zone II
Zone II represents the Tropical Rainforest biome, requiring adaptations to cope with shallow leached topsoil (buttress roots for mechanical support) and excessive rainfall (drip-tip leaves to shed water efficiently).
Dense canopy trees grow extremely tall to compete for light, requiring wide buttress bases to stabilize in thin upper soil layers.
3
Identify environmental stressors for Zone III
Zone III represents the Guinea/Sudan Savanna biome, requiring pyrophytic and xeromorphic adaptations such as thick insulating corky bark, deciduous leaf-shedding habits, and subterranean lignotubers/rootstocks.
Periodic grass fires destroy above-ground biomass; insulating bark and underground storage organs allow rapid post-fire regeneration.

Key Concept

Structural and physiological plant adaptations across aquatic, forest, and savanna biomes
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Topics

Biomes and Aquatic/Terrestrial Habitats

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