Read the text.

The flying beetle known as the firefly or lightning bug is named for its most noticeable feature: its nighttime bioluminescence, or glow. The firefly's light-producing organ contains calcium, the pigment luciferin, the light-producing enzyme luciferase, and the chemical adenosine triphosphate (ATP). When oxygen is added to this mix, it creates light, and the insect glows. Scientists don't fully understand how the firefly makes its light blink, but one theory is that the firefly turns the light on and off by controlling the input of oxygen into the light-producing organ.
Which organizational structure does this text primarily use?

This text primarily uses a cause and effect organizational structure. It presents information about the firefly's bioluminescence and then explains how the addition of oxygen creates light. The text also discusses a theory about how the firefly controls the blinking of its light by controlling the input of oxygen.