[Campbell Biology P.820] A fossil leaf found in a region that experienced intermittently ver... | Practice Question

A fossil leaf found in a region that experienced intermittently very dry and very swampy conditions in the geological past has stomata found only on its upper epidermis. Based on the principles of leaf anatomy and adaptation discussed, was this leaf more likely from a desert plant or a floating aquatic plant? Explain why.

  • A: Desert plant, because stomata on the upper surface would maximize water retention in dry conditions.
  • B: Floating aquatic plant, because stomata on the upper surface would facilitate gas exchange with the atmosphere while the lower surface is submerged.
  • C: Desert plant, because the upper epidermis is more exposed to sunlight, aiding photosynthesis in dry conditions.
  • D: Floating aquatic plant, because stomata on the upper surface would help in expelling excess water from the swampy environment.

Explanation

The text mentions stomata as 'major avenues for the evaporative loss of water' and for 'exchange of CO2 and O2'. For a floating aquatic plant, the lower surface of the leaf is submerged in water, making stomata on the upper epidermis essential for gas exchange with the atmosphere. In contrast, desert plants typically reduce water loss by having stomata on the lower epidermis, in crypts, or fewer stomata overall, to minimize direct exposure to intense sunlight and dry air.