Question

the simplest body plan a sponge can have; have the least surface area for nutrient & gas exchange
the large opening at the top of a sponge that lets wastewater out
a soft, flexible protein that makes up the frame so some sponges

Explanation:

1. The first definition refers to the asconoid body plan of sponges, which is the simplest form with minimal surface area for exchange.
2. The second definition describes the osculum, the large exit opening for wastewater in sponges.
3. The third definition refers to spongin, the flexible protein that forms the skeletal framework of some sponges.

Answer:

1. Asconoid body plan
2. Osculum
3. Spongin