The first action spectrum was made by T.W.Engelmann, who split light into its components by the prism, and then illuminated cladophora placed in a suspension of aerobic bacteria.He found that bacteria accumulated in the region of blue and red light of the split spectrum.

Introduction:
Englemann's experiment in 1883 provided the first action spectrum of photosynthesis. Through his study, he aimed to determine the specific wavelengths of light that are most effective in driving the process of photosynthesis in plants. Englemann's experiment involved the use of a single-celled green alga called Spirogyra and a prism to separate light into its different wavelengths.

Procedure:
Englemann's experiment consisted of the following steps:

1. Selection of Spirogyra: Englemann chose Spirogyra as the test organism due to its ability to perform photosynthesis and its transparency, which allowed him to observe the distribution of oxygen bubbles.

2. Preparation of the sample: A strand of Spirogyra was placed on a microscope slide and covered with a cover slip. The slide was then placed under the microscope for observation.

3. Illumination with different colors: Englemann used a prism to separate white light into its component colors (wavelengths). He then directed each color of light onto the Spirogyra sample one at a time. This allowed him to determine the response of Spirogyra to different wavelengths of light.

4. Observation: Englemann observed the Spirogyra sample under each color of light and noted the distribution of oxygen bubbles produced by the organism. Oxygen bubbles are an indicator of photosynthetic activity.

5. Results: Englemann found that the Spirogyra sample produced the most oxygen bubbles when exposed to light in the red and blue regions of the spectrum. The green region showed the least amount of photosynthetic activity.

Analysis:
Englemann's experiment provided the first action spectrum of photosynthesis, which showed the relative effectiveness of different wavelengths of light in driving the process. The results indicated that red and blue light are the most efficient in promoting photosynthesis, while green light is the least effective.

Significance:
Englemann's experiment laid the foundation for understanding the role of different wavelengths of light in photosynthesis. It demonstrated that plants have specific pigments, such as chlorophyll, that absorb light in the red and blue regions of the spectrum. This knowledge has since been utilized in various applications, such as optimizing artificial lighting for plant growth and understanding the impact of light pollution on ecosystems.

Overall, Englemann's experiment was a crucial milestone in the study of photosynthesis, providing valuable insights into the action spectrum and the importance of light wavelength in driving this vital process in plants.