Babies born slightly under 1,500 grams (3 pounds 5 ounces) are considered:

prokaryotic cells do not have a nucleus in which the dna is stored in, it floats freely inside the cell.

eukaryote cells do have a nucleus in which the dna is stored in.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.