Engelmann’s experiment with Spirogyra demonstrated thatA. The full spectrum of sunlight is needed for photosynthesisB. Only red wavelengths are effective in causing photosynthesisC. Only blue wavelengths are effectiveD. Both blue and red wavelengths are effective

Engelmann's experiment with Spirogyra demonstrated that:

D. Both blue and red wavelengths are effective in causing photosynthesis.

In Engelmann's experiment, he used a prism to disperse light into different colors and directed these colors onto Spirogyra algae. He noticed that the algae produced more oxygen bubbles (indicating higher rates of photosynthesis) in the areas where blue and red light were present, suggesting that these wavelengths are the most effective for driving photosynthesis. This experiment helped to determine the action spectrum of photosynthesis and showed that chlorophyll absorbs light most efficiently in the blue and red parts of the spectrum.