Which term describes organisms that are active during the day?

The term that describes organisms that are active during the day is "diurnal." This term specifically refers to species that have adapted their behavior to be primarily active in daylight hours. Examples of diurnal organisms include humans, many species of birds, and a variety of insects that take advantage of sunlight for foraging, mating, and other activities.

In contrast, nocturnal organisms are adapted to being active at night, utilizing lower light levels for their activities, which often helps them avoid predators and hunt for food in the dark. Crepuscular organisms are active during dawn and dusk, capitalizing on the transitional periods of light that can provide advantages in hunting or avoiding predation. Arrhythmic does not refer to a specific activity pattern related to time of day but rather suggests an irregular rhythm in behaviors or activities. Therefore, diurnal is the appropriate choice for describing organisms that are actively engaged in activities during the day.