PTE Academic Reading Test 5

For centuries, the precise mechanism behind the brilliant colours of butterfly wings puzzled naturalists. It was long assumed that these vivid hues were produced solely by pigments, much like the dyes used in fabrics. However, advances in microscopy revealed a more intricate explanation. Many of the most striking colours, particularly the iridescent blues and greens, are not the result of pigment at all. Instead, they arise from microscopic structures on the surface of the wing scales. These structures are arranged in regular, repeating patterns that interact with light in a phenomenon known as structural colouration. When light strikes these patterns, certain wavelengths are reflected and amplified while others are cancelled out. The specific colour we perceive depends on the spacing and arrangement of the microscopic ridges. Because the effect relies on the angle of incoming light, structurally coloured wings often appear to shift in hue as the butterfly moves. This explains why such colours seem to shimmer in a way that pigment-based colours cannot. Researchers have taken great interest in this natural engineering, hoping to mimic it in the design of new materials. Potential applications range from fade-resistant paints to advanced optical sensors. By studying how butterflies manipulate light, scientists believe they may unlock more sustainable ways to produce colour, free from chemical dyes that can harm the environment.

What is the main reason that the iridescent colours of butterfly wings appear to shift?

1. A.The wings contain unusually concentrated pigments.
2. B.The colours depend on the angle at which light strikes the wing structures.
3. C.The butterfly changes the chemical composition of its scales while moving.
4. D.The wings reflect every wavelength of light equally.

The correct answer is shown in your review when you finish the test.