On Monday the class set up two bunged boiling tubes of hydrogencarbonate indicator, one with a sprig of pondweed and one without, in front of an LED lamp on a plug-in timer that switches on and off every twelve hours. A school tablet on a stand records the tubes in time-lapse for 48 hours, with a dim green bulb, far too weak for the pondweed to photosynthesise faster than it respires, so the camera can see through the dark hours. On Wednesday the teacher plays the two days back in under two minutes: the class watches the pondweed tube turn from orange-red to purple under the lamp, drift back through red to yellow overnight and turn purple again when the lamp comes on, while the tube without pondweed stays orange-red. The teacher replays each switch of the lamp and asks what the colour says about carbon dioxide in the tube, and students fill in a strip in their books showing the colour every six hours, with a sentence on photosynthesis and respiration for each.
Tools: Built-in camera (slow motion and time-lapse) Nine ideas for your own version in Generate
This page is one of a growing set of PICRAT examples by cell, subject and grade. Page maintained by Andy Perryer.