Apples grow on trees, tomatoes grow on vines.
Apples are hard, tomatoes are squishy.
The seeds in an apple are not eaten, whereas you barely notice the seeds in a tomato.
Tomatoes are acidic, apples are not.
The skins are quite different. Apple skins tend to be thicker, and hard to chew and digest.
Apple: Whitish flesh. Tomato: Red or green flesh.