If I read his request correctly he needs something by tomorrow.
So maybe the plant idea is not suited, unless he only needs to submit his idea by tomorrow.
Light sensitivity might not be so bad though, but maybe use a light sensitive bug. Put it in a petridish and describe how it reacts under different light conditions. No covering, petridish covered, semi-covered.
Can throw in cooling too. Put Icecube in one side. Note what it does.
Might try heating too, but don't light a fire underneath a petridish...that is just cruel.
Just need to find light sensitive bug, petridish and an icecube.
You won't get an A though.