Formal and informal writing.
Formal writing is a type of writing which is mostly used in professional or other academic writings. Informal writing on the other hand is a type of writing which is mostly used while having a casual conversation.
The sentence ‘Carnivorous plants use an unorthodox method of obtaining nutrients’ is a formal sentence. If we have to rewrite it as informal one, it would be something like this ‘Carnivorous plants are insectivorous plants and they prefer unorthodox method to obtain nutrients.’
The sentence ‘They trap insects specially constructed plant structures, which then secrete digestive juices’ is an informal one. To make it as a formal sentence, we have to avoid using pronoun. So it would be, ‘Carnivorous plants trap insects by constructing plant structures, followed by secreting digestive juices.’