Final answer:
The biological rhythm that continues in the absence of environmental cues is the free-running rhythm, and when referring to a near-24-hour cycle, it is known as the circadian rhythm. The correct option is 4) free-running rhythm.
Step-by-step explanation:
In the absence of environmental cues, the biological rhythm that persists is called a free-running rhythm. This is observed in circumstances where external time cues, known as zeitgebers (which include light, temperature, and social interactions), are absent. The most common type of free-running rhythm is the circadian rhythm, which continues to run on an approximately 24-hour cycle even without external light-dark cues. In humans, for example, the circadian rhythm governs cycles of sleep and wakefulness, body temperature, blood pressure, and other physiological processes. This rhythm is primarily controlled by the biological clock in the brain. When an organism, such as a plant, is transferred to a dark environment, its circadian rhythm will persist for some time in the absence of light, driving activities like flower opening and closing based on its internal clock.