Which term refers to rhythms that are determined by external environmental factors?

The term that accurately describes rhythms determined by external environmental factors is exogenous rhythm. These rhythms are influenced by various external cues, such as light, temperature, and seasonal changes, rather than being generated internally by the organism itself.

In contrast, circadian rhythms are a specific type of biological rhythm that typically cycle approximately every 24 hours, and while they can be influenced by environmental factors such as light-dark cycles, they are fundamentally based on an organism's internal clock. Endogenous rhythms, on the other hand, are those arising from internal biological processes and are intrinsically controlled by the organism, independent of external stimuli. Vernalisation refers specifically to the process whereby exposure to a prolonged period of cold is required for certain plants to flower, but it does not encompass the broader concept of rhythms governed by external factors.