What is: an organ that no longer functions in an organism and which is homologous to a functioning organ in another organism

I think the answer is Vestigial structures

Vestigial structures

Explanation:

Vestigial structures are anatomical structures of organisms in a species which are considered to have lost much or all of their original function through evolution. ... Vestigial structures are often referred to as vestigial organs, though not all of them are actually organs.

the answer is 1. photosynthesis. glad to

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.