In order to assist with developing content comprehension and vocabulary, your students can become experts in a particular field and then publish their own definition in a class dictionary.
When you come across a difficult term in Science, allocate a student to be an expert on that particular concept. They need to research the term, take a page from the class Science Definition Dictionary and then write their own definition for the class to refer to. They also draw the concept in anyway that they feel depicts the idea.
They are then known as the class expert for that concept and if students need any further clarification, they need to see the author of that definition. Collate the dictionary together with split pins or in a folder with plastic sleeves so concepts and terms can be continuously added.