the effect on shrubs growing in one area if they are treated with a compound that blocks electron flow through the electron transport chains of chloroplasts. Provide reasoning to justify your prediction.

Blocking electron flow prevents the generation of a proton (H+) gradient required for ATP synthesis, and this ATP is in turn exploited by photosynthetic cells to produce organic molecules. In consequence, the blockage of this process would have critical implications for the survival and growth of the shrubs.  

Explanation:

In plant photosynthetic reactions, photons from sunlight excite (energize) electrons from chlorophyll molecules located in the thylakoid sacs of the chloroplast. Subsequently, the high-energy electrons move across the electron transport chain that pumps protons (H+) to generate a gradient across the thylakoid membrane. This proton gradient is then exploited by plant cells to synthesize ATP, which is in turn used to create energy-rich organic molecules (e.g., sugar). In consequence, blockage of the electron flow would be critical for the survival and growth of the shrubs.