Problem 20 - Objective Biology for NEET

Question

The first action spectrum of photosynthesis is described often as an experiment of (a) Jan Ingenhousz (b) Joseph Priestley (c) Von Sachs (d) Engelmann

Step-by-Step Solution

Answer

The correct answer is (d) Engelmann.

Step 1: Recall Historical Facts

Remember the famous experiments of photosynthesis and to whom they are attributed. The first action spectrum of photosynthesis refers to the first experiments that proved which colors (wavelengths) of light resulted in the most photosynthesis.

Step 2: Identify the Scientist

From the given options, only Engelmann is associated with the first action spectrum of photosynthesis. This experiment, conducted by Theodor Wilhelm Engelmann in the 1880s, demonstrated that the rate of photosynthesis was greater under violet-blue and red light.

Key Concepts

Engelmann's Experiment

Theodor Wilhelm Engelmann, a German botanist in the 1880s, ingeniously used a simple organism to unravel a complex process. His clever use of a filamentous alga, Spirogyra, along with aerobic bacteria, allowed him to determine which wavelengths of light were most effective for photosynthesis. Engelmann split light into its spectral components with a prism and directed it onto the algae. He then observed areas where bacteria clustered, indicating higher oxygen production and, thus, more photosynthesis.

Engelmann observed that bacteria congregated mainly around the parts of the algae exposed to red and blue light. This experiment effectively crafted the first action spectrum of photosynthesis, illustrating the different efficiencies of various wavelengths of light in driving the photosynthetic process. This key experiment laid out the foundation for understanding how plants utilize light energy, which is crucial in fields ranging from agriculture to renewable energy research today.

Photosynthesis Wavelength

Photosynthesis, the process by which plants, algae, and some bacteria convert light energy into chemical energy, is selective in its use of the electromagnetic spectrum. The photosynthesis wavelength concept emerged from research like Engelmann's. We now know that plants primarily absorb light in the blue (approximately 430-450 nm) and red (approximately 650-700 nm) ranges. This is due to the presence of chlorophyll, the pigment responsible for photosynthesis, which strongly absorbs these colors.

In the visible spectrum, chlorophyll reflects and transmits more green light, which is why plants appear green to our eyes. Understanding the wavelength dependency of photosynthesis has been critical for applications such as designing efficient artificial lighting in plant cultivation and optimizing solar cells that mimic photosynthetic processes.

Historical Experiments in Photosynthesis

The quest to understand photosynthesis has been marked by several landmark experiments throughout history. Prior to Engelmann's work, other scientists made significant contributions. They include Joseph Priestley in the 1770s, who discovered that plants release oxygen; Jan Ingenhousz, who identified light as essential for this process a few years later; and Julius von Sachs in the 19th century, who demonstrated the production of starch within leaves in the presence of light.

Each of these groundbreaking experiments paved the way for a deeper elucidation of photosynthesis. They set the stage for Engelmann's experiment, which interlinked the type of light with photosynthetic activity. Collectively, this body of work underpins modern botany, ecology, and agricultural science, highlighting the powerful role that methodical inquiries and experimental innovation have played in unveiling the intricacies of life on Earth.