IB DP Biology- B4.1 Adaptation to environment- IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
✅ Answer: (D) Increasing the wind speed
Question
By the end of the 19th century in England, the dark form of the moth Biston betularia formed up to $98 \%$ of the total population in industrial areas. From 1970, the percentage of dark forms decreased significantly. What is an explanation for the decrease?
A. An increase in environmental pollution killed the dark forms more than the light forms.
B. Reduction of pollution resulted in greater camouflage for light forms of the moth.
C. Dark forms could no longer find mates.
D. Light forms had superior feeding mechanisms.
▶️Answer/Explanation
Answer: B. Reduction of pollution resulted in greater camouflage for light forms of the moth.
Explanation:
Biston betularia, or the peppered moth, is a classic example of natural selection in response to environmental changes. During the Industrial Revolution, dark-colored moths became more common in polluted areas because they were better camouflaged on soot-covered trees, avoiding predation. After 1970, environmental regulations reduced pollution, cleaning the trees and exposing dark moths to predators again, leading to a decline in their numbers.
Option Evaluation:
A. Incorrect – Pollution did not start killing dark moths directly. The issue was camouflage, not toxicity. The dark moths were more visible to predators after pollution decreased.
B. Correct – As pollution decreased, tree bark became lighter, making light-colored moths better camouflaged. This improved their survival and reproductive success, leading to an increase in their numbers and a decrease in dark moths.
C. Incorrect – There’s no evidence that mating issues caused the decline in dark forms. Mate choice was not a major factor here; predation and camouflage were the driving forces.
D. Incorrect – Feeding mechanisms did not change between the forms. Both moth types feed the same way; survival was determined by visibility to predators, not food acquisition.