Alveoli are described as sacs shaped like:

1. Alveoli cluster at the end of the ducts. 2. Their arrangement suggests a familiar fruit. 3. An alveolus is one of the many small, grape-like sacs attached to the alveolar ducts. 4. So the answer is grapes. _Source: OpenStax 'Anatomy and Physiology 2e', Ch 22 'The Respiratory System'_