Cooperation of the two photosystems of the chloroplast is absolutely required for

The cooperation of two photosystems is required for the upward electron transport from water to ${\mathrm{NADP}}^{+}$ through the two photosystems. Photosystem I is more directly associated with the reduction of ${\mathrm{NADP}}^{+}$, whereas the photosystem II is more closely associated with the  extraction of electrons from water.