Examkin

Question

Difficulty: EasyEvolution and Adaptation

Which of the following best explains how desert cacti evolved spines instead of broad leaves over many generations?

  1. A
    Individual cacti actively transformed their leaves into sharp needles during drought periods to prevent water loss.
  2. Ancestral plants with narrower, spine-like leaf variations conserved water better and reproduced more successfully in arid environments.Answer
  3. C
    The spine trait is genetically dominant, which automatically caused it to become the most common trait in the population regardless of environmental conditions.
  4. D
    Individual plants hardened their leaves through frequent sun exposure during their lifetime and passed those hardened leaves to their offspring.

Answer

Ancestral plants with narrower, spine-like leaf variations conserved water better and reproduced more successfully in arid environments.
Natural selection operates on preexisting genetic variations within a population. Ancestral desert plants that possessed smaller, spine-like leaves experienced less water loss through transpiration compared to broad-leafed plants. As a result, these individuals survived droughts more effectively and passed their heritable traits to subsequent generations, leading to the prevalence of spines.

Step-by-Step Solution

1
Identify the environmental pressure and adaptation mechanism
Arid desert conditions create intense selective pressure to conserve moisture, favoring structures that minimize surface area and transpiration.
Evolution by natural selection requires an environmental pressure acting on preexisting genetic variations.
2
Differentiate between population-level natural selection and individual acquired changes
Populations evolve over generations because individuals possessing advantageous heritable variations survive and produce more offspring.
Individual organisms do not consciously adapt or pass down non-genetic acquired characteristics.

Key Concept

Natural Selection and Structural Adaptations
Estimated Time:45s
Rate this question

Topics

Evolution and Adaptation

More questions from this topic