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Difficulty: MediumVertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

An adult toad (*Bufo regularis*) and a rainbow lizard (*Agama agama*) are both poikilothermic vertebrates, yet the lizard is significantly better adapted to surviving and reproducing in arid terrestrial habitats. Which set of anatomical features primarily accounts for the lizard's independence from aquatic environments?

  1. Dry keratinized epidermal scales and an amniotic egg with a protective shellAnswer
  2. B
    A four-chambered heart that completely separates oxygenated and deoxygenated blood
  3. C
    Smooth glandular skin used for cutaneous respiration alongside a two-chambered heart
  4. D
    Classification under *Agama Agama* with external fertilization in open water

Answer

Dry keratinized epidermal scales and an amniotic egg with a protective shell
Reptiles are fully terrestrial poikilotherms because their dry, keratinized epidermal scales prevent evaporative water loss and their shelled amniotic eggs enclose fluid-filled membranes that protect developing embryos from drying out.

Step-by-Step Solution

1
Analyze the structural differences between Class Amphibia (toad) and Class Reptilia (lizard) regarding water conservation.
Amphibians have moist, permeable skin prone to water loss, whereas reptiles possess dry, keratinized epidermal scales that prevent desiccation.
Epidermal covering determines physiological tolerance to dry terrestrial air.
2
Evaluate the reproductive adaptations of both poikilothermic classes.
Amphibians rely on water or moist surroundings to lay non-cleidoic eggs, while reptiles lay shelled amniotic eggs that retain moisture on dry land.
Amniotic eggs eliminate the necessity of returning to open water bodies for larval development.

Key Concept

Adaptive structural features distinguishing Amphibia and Reptilia in terrestrial environments
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Topics

Vertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

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