aperture

1. We could relate aperture to the pupil because our eyes can either expand or shrink depending on what we are looking at. Which with aperture you can shrink and enlarge it just like you can with your pupils. That's why I believe the pupil can closely relate to the aperture.

2. The smaller the aperture, less light. The higher the aperture, more light or exposure.

3. It affects the depth because the smaller the number aperture the blurrier the background.