2.20 describe experiments to investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll

2.20 •test for starch: •boil the leaf to kill and stop chemical reactions

                                 •put the leaf in a boiling tube with ethanol and heat in a water bath, killing the chlorophyll. It should turn white

                                 •rinse the leaf in cold water, add a few drops of iodine solution. If starch is present, it will turn blue-black

        •testing the need for chlorophyll: •take a variegated leaf and record the green and white parts

                                                            •test for starch (green will turn blue-black, white goes brown)

        •testing the need for carbon dioxide: •you need a sealed bell jar, soda lime, light and a plant

                                                                   •the soda lime will absorb the CO2 in the air of the jar

                                                                   •leave for a while and then test the leaf for starch

                                                                              •it won’t turn blue black, proving CO2 is needed

        •testing the need for light: •grow a plant in the dark, and then test for starch

                                                            •it won’t turn blue-black, showing light is needed

        •oxygen production in photosynthesis: •light is set at a specific distance

                                                                      •pondweed is left to photosynthesise for a set time

                                                                                •as it photosynthesises, the oxygen released

                                                                                 collects in the capillary tube  

                                                                      •at the end, the syringe is used to draw the gas bubble

                                                                        in the tube and the gas bubble tube is measured

                                                                                •this is proportional to the volume of O2 made

                                                                       •the experiment is repeated with the light source

                                                                        placed at different distances

                                                                                •the apparatus can be altered to measure the

                                                                                 effect of temperature and carbon dioxide