Final answer:
The alveolar sac is the structure within the respiratory system that looks like a bunch of grapes. Each sac contains multiple alveoli, which are the actual sites where gas exchange occurs with the bloodstream.
Step-by-step explanation:
The structure similar to a "bunch of grapes" in the respiratory system is the alveolar sac. Terminal bronchioles connect to respiratory bronchioles, which then subdivide into several alveolar ducts. These ducts open into clusters of alveoli, which together form alveolar sacs. An alveolar sac resembles a bunch of grapes and is tethered to the end of the bronchioles.
Each alveolar sac contains 20 to 30 spherical alveoli and facilitates gas exchange with the blood through capillaries. The alveoli are the site of critical oxygen and carbon dioxide exchange in the lungs. Alveoli are minuscule, thin-walled structures that are directly in contact with the capillary's thin, one-cell thick walls, allowing for efficient gas transfer.