Question

Some modern eukaryotes, such as giardia intestinalis, lack mitochondria but still retain some of the genes for mitochondrial proteins. what logical conclusion can be drawn about these organisms?

Answer 1

because proteins are necessary for our body to function that's why they retain them.

Answer 2

In the given question, it suggests that at one point at the time of evolution, Giardia intestinalis contained mitochondria.  

The existence of genes for mitochondrial proteins indicates that these genes are a remnant of the time when these bacteria comprised mitochondria. With time and various mutations, the bacteria may have lost the mitochondria, however, didn't essentially eliminated each gene associated with mitochondria.