During the light dependent stage of photosynthesis, hydrogen ions and electrons are released by the photoactivation of chlorophyll and the photolysis of water. These are added to the carrier molecule, NADP, changing it from an oxidised state to a reduced state, as shown in Fig. 1.1. 2H⁺ + 2e⁻ + oxidised NADP → reduced NADP [Figure 1.1] DCPIP is a blue dye which becomes colourless when reduced by hydrogen ions and electrons, as shown in Fig. 1.2. oxidised DCPIP (blue) → reduced DCPIP (colourless) [Figure 1.2] A student used DCPIP to determine if the reactions in the light dependent stage had occurred in a suspension of chloroplasts. • The suspension of chloroplasts was prepared by grinding, filtering and centrifuging a sample of leaves with ice-cold extraction medium. • Four tubes covered in foil were set up containing the mixtures shown in Table 1.1. [Table 1.1] • The tubes were illuminated through a thin glass tank filled with water as shown in Fig. 1.3. [Figure 1.3] • The foil was removed from tubes 1, 2 and 3, but left on tube 4. • A timer was started immediately. • After 10 minutes the colour in each tube was observed and recorded. Table 1.2 shows the student's results. [Table 1.2]