In the ecological pyramid organism A represents

photosynthetic organisms

Explanation:

These are autotrophs organisms that use carbon dioxide and water, and with the help of solar energy, they produce nutritive material and release oxygen.

This is known as the process of photosynthesis and it is done in the organs of the plants that contain chloroplasts.

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.