This compare and contrast map, with the key included, can be used to introduce plankton, or be used for remediation, or be used to summarize an activity related to plankton or energy flow in an ecosystem. The document can easily be made into a PDF document for annotation in Preview, or Adobe.
Do this together as whole-group, or have the kids work on it in small groups. Maybe do a word sort before hand to practice the vocabulary such as photosynthesis, carbon cycle, holoplankton, or meroplankton. (I try to spiral my curriculum, so I try and make what we are learning currently relevant to what we've learned in the past, as well as get my kids ready for what we are learning in the future.) If that's an issue, this can easily be modified.