The study of plants is interesting and amazing... and just because you may have chosen to study science online doesn't mean that you can't study plants and reap the benefits of nature as your science lab.
1)Go outdoors to study photosynthesis by looking at leaves
2) Study special plants such as - evergreens, pricly plants, climbers, and needle leaves
3) Study roots and stems by pulling up a few plants and comparing their roots.
Use online science games on the various subjects you studies to drill and review the concepts that were introduced.
Do an experiment that also examines the parts of plants that you studied this week.