the buffer letters (-y in this case) is only used if the word ends with a vowel, ekmek doesn't end with a vowel, so you don't need -y
because of the vowel harmony you need to use i, not ı
words ending with p ç t k mutate to b c d g
so there are a lot of reasons :) please read https://www.duolingo.com/comment/7738396
I eat bread: Ben ekmek yerim.
I eat the bread: Ben ekmeği yerim.
The suffix type determines the tense of the word.
In this case we are specifically talking about 'the bread' (on the table, for example) rather than generic bread (for example simply saying that in general, I eat the bread).