Question

The ______ is a vital organ, and its functioning is essential to life.

Answer 1

The heart is a vital organ, and its functioning is essential to life.
All your other organs may fail, and you will still be alive. Even if your brain stops working, and your heart is healthy, you will be alive in the vegetative state where you won't be conscious at all. However, once your heart stops working, you die, which means it is the most important organ in your body.