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Difficulty: HardMorphological and Physiological Adaptations to Environments

Desert succulents and submerged aquatic plants experience vastly different environmental pressures regarding water availability and gaseous exchange. Which of the following processes represents a physiological adaptation in desert succulents that minimizes transpirational water loss during carbon fixation?

  1. Fixing carbon dioxide at night into malic acid via Crassulacean Acid Metabolism so stomata remain closed during the dayAnswer
  2. B
    Absorbing atmospheric water vapor through non-vascular rhizoid structures instead of internal vascular root tissues
  3. C
    Translocating manufactured organic solutes upward through xylem vessels to leaf tissues during peak sunlight hours
  4. D
    Releasing oxygen gas as a byproduct during dark reaction pathways to maintain internal turgor pressure

Answer

Fixing carbon dioxide at night into malic acid via Crassulacean Acid Metabolism so stomata remain closed during the day
Fixing carbon dioxide at night into malic acid via Crassulacean Acid Metabolism allows desert succulents to open stomata during cooler night hours, significantly reducing transpirational water loss compared to daytime stomatal opening.

Step-by-Step Solution

1
Identify the primary physiological challenge faced by desert succulents
Desert succulents must fix carbon dioxide for photosynthesis while limiting water loss through transpiration in high daytime temperatures.
Stomatal opening during the day causes severe water loss due to high transpiration rates.
2
Evaluate the metabolic mechanism of Crassulacean Acid Metabolism (CAM)
CAM plants open stomata at night when temperatures are lower, taking up CO2CO_2 and storing it as malic acid in vacuole storage, then closing stomata during the day.
This temporal separation of initial carbon fixation and the Calvin cycle conserves significant amounts of water.
3
Distinguish between physiological adaptations and morphological or non-applicable plant features
CAM is a biochemical/physiological process, distinguishing it from structural features or incorrect tissue mechanisms described in other options.
Rhizoids are non-vascular structures in bryophytes, xylem conducts water (not sugars), and photolysis generates O2O_2 in light reactions.

Key Concept

Crassulacean Acid Metabolism (CAM) as a physiological adaptation to arid environments
Estimated Time:1m 30s
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Topics

Morphological and Physiological Adaptations to Environments

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