托福口语 Task 3

In biology, the concept of 'phenotypic plasticity' refers to the ability of a single genotype to produce different phenotypes in response to different environmental conditions. This means that an organism's physical or behavioral traits can vary depending on factors like temperature, food availability, or light, even if its genetic code remains unchanged. Phenotypic plasticity allows organisms to adapt to changing environments without genetic evolution, often within a single generation. It is a key mechanism for survival in dynamic habitats.

Professor: Let me give you a concrete example from a study on water fleas. Water fleas are tiny crustaceans that live in ponds. When predators like fish are present in the water, the water fleas detect chemical cues released by the fish. In response, they develop a protective helmet and spikes on their heads. These structures make them harder for fish to swallow. However, when no predators are present, the same water fleas grow smooth, rounded heads. This change is not genetic—they have the same DNA. It’s purely driven by the environment. So, in just a few days, the water fleas alter their physical appearance to match the threat level. This is a classic case of phenotypic plasticity.