When is "the" required before nouns?
I was presented with the phrase "Turtles do not run." I translated it to "Tortugas no corren." This was marked wrong, the correct answer being "Las tortugas no corren." Another example is "Ella va a la cama." which I translated to "She goes to the bed." This too was marked wrong with the correct translation stated as "She goes to bed." What if it was "Ella va a el perro." You wouldn't say "She goes to dog". So confusing. Is "the" always required before a noun in spanish? Does it matter if the noun is proper or improper?
Your first answer was actually wrong. When you say "Turtles do not run", you are referring to turtles in general. English does not use a definite article when talking about fundamental properties of an entire class of things, people or animals, but Spanish does. The definite article "las" in "Las tortugas no corren" is not optional, just like it would mean something different in English if you said "The turtles don't run."
"Ella va a la cama." without additional context clearly means that she goes to bed. I guess in some specific contexts it may also mean that she goes (i.e. walks) to a specific bed. Maybe one can say: "Ella va a la mesa. Después, ella va a la cama." But my Spanish is not good enough to know whether that is correct, as there are other words for "go" in Spanish and it may not be correct to use "va" ("ir") in such a context.
In general, I feel that there is too much second-guessing involved in responding to questions. Sometimes we are expected to get nuances right, and sometimes we are expected to give totally wrong translations such as the infamous "you all" in order to demonstrate we have understood a detail of grammar. That's inconsistent.