Besides transpiration what else do plants do

Im in year 12 and for my Biology assignment we have to do and EEI but it has to be on ecolgy. I need some suggestions that can be done in 4 week.
Cheers

photosynthesis
grow
produce the products we use from plants
reproduce
give us oxygen
respiration
tropisms

Respiration is always occuring in plants, this process will release CO2 and will be dominant over photosynthesis at night time. When the sun rises photosynthesis rate will increase and this process will use CO2. Plants are not the "lungs" of the earth as they both consme and release O2 and CO2, however they do act as a resevoir for carbon.