In the sentences below, can I use a singular noun or must the nouns of the sentences be plural, and if so why?
He likes hamburgers.
She likes lions.
Are these sentences wrong?
He likes hamburger.
She likes lion.
Commentors have noted that "hamburger" and animal names in the singular can be used as uncountable nouns. Let me assume for a moment, though, that this is not what you meant. Let's use an example that does not have this ambiguity:
Right: He likes cars.
Wrong: He likes car.
In general in English, a singular noun must have an article in front of it, or an adjective indicating one or none. So you could say:
He likes the car.
But this means something very different from the first sentence above. "He likes cars" means that he likes cars in general. It probably means that he enjoys the sensation of driving, or that he likes to do auto mechanics as a hobby, or perhaps that he collects cars as a hobby. Or in context it might mean that he prefers driving or riding in a car to taking a bus or riding a horse or whatever alternatives are available. But "He likes the car" means that he prefers one particular car, like he prefers a Ford Mustang over a Chevy Cavalier.