Both my biology and AP Environmental Science classes have several important terms and concepts throughout each unit. Without a basic understanding of these terms, it's not possible for students to answer deeper level questions that require making connections, application, and problem solving.
One of the tools that I like to use for vocabulary is Quizlet. Quizlet is free, although a $24.99/year teacher account offers some more powerful features that I would argue are worth the money. It is available both on a web browser and on the iPad. Similar to flash cards, Quizlet offers several ways for students to practice their understanding of key terms in more interactive ways.
After making an account, students can join a class that you have set up on Quizlet and can study from "sets" or groups of vocabulary words that you have prepared. Words in a set can be studied as traditional flash cards or students can play a variety of games to help master a set of words.
This feedback allows me to target specific terms and concepts that my students are struggling with in warm-ups and closers. It is also very easy for a student or teacher to "star" and isolate specific terms to study that might need more attention. Quizlet itself can also be great just as a warm up or closer.
Quizlet has a huge amount of shared sets that can be used as well, so creation form the ground up may not be necessary. For instance, sets for the APES textbook we use are readily available from other teachers and can be transferred to your classes.
While Quizlet is just one of several apps that help with vocabulary, I find it to be one that gives me feedback that can help me modify my instruction to help students reach mastery of key terms and vocab.