Question

Which of the following pigments resemble the action spectrum produced on the basis of Engelmann experiment? A. Chlorophyll a B. Chlorophyll b C. Xanthophyll D. Carotenoids (a) \(\mathrm{A}\) and \(\mathrm{C}\) only (b) A and B only (c) Only A (d) \(\mathrm{C}\) and \(\mathrm{D}\) only

Short answer

The correct answer is (b) A and B only. Both Chlorophyll a and Chlorophyll b absorb light primarily in the blue and red spectrum, which matches the active regions discovered in Engelmann's experiment.

Step-by-step solution

Understand Engelmann's Experiment

Engelmann's experiment illuminates the relation between the color of light and the rate of photosynthesis. More specifically Engelmann discovered that bacteria clustering with high frequencies around the regions exposed to red and blue/violet light, thus indicating a high rate of photosynthesis at those regions. Further implying that the pigments responsible are most reactive, or absorb these colors best.

Identify the Photosynthetic Pigments

Four major pigments are found in the photosynthetic process: Chlorophyll a, Chlorophyll b, Carotenoids, and Xanthophyll. \n- Chlorophyll a, the main pigment, absorbs light primarily in the blue and red wavelengths. \n- Chlorophyll b aids in photosynthesis by extending the range of light a plant can use, absorbing light primarily in blue and orange/red wavelengths but less efficiently. \n- Carotenoids, including xanthophyll and carotenes, absorb light in the blue/violet wavelengths and dissipate excessive light energy that could damage chlorophyll. They do not contribute significantly to photosynthesis by themselves.

Match the Pigments to Engelmann's Action Spectrum

Based on Engelmann's experiment, the wavelengths promoting the most photosynthesis were in the blue/violet and the red spectra of light. Chlorophyll a would be a match as it absorbs light in the red and blue wavelengths. Chlorophyll b also absorbs light in the red and blue spectra, thus, it also matches Engelmann's action spectrum. Therefore, the correct response should be only the pigments that absorb light primarily in the blue and red spectrum, namely Chlorophyll a and Chlorophyll b.

Key concepts

Engelmann's Experiment

Engelmann's experiment is a classic study in the field of photosynthesis. It carefully explored how different wavelengths of light affect the process of photosynthesis in green algae. To do this, Engelmann shone light through a prism, creating a spectrum, and directed it onto strands of algae. He then sprinkled oxygen-loving bacteria on the algae and observed their clustering patterns. The bacteria gathered notably in areas exposed to red and blue/violet light. This pattern illustrated that photosynthesis occurs most efficiently under these wavelengths.

Engelmann's work showed that certain pigments in the plant absorb light and drive photosynthesis, especially in the red and blue light bands. This landmark experiment helped identify the pigments that are active in photosynthesis, key to understanding which colors of light plants use most effectively.

Chlorophyll a

Chlorophyll a is the most critical pigment in photosynthesis. It plays a central role as the primary light-absorbing pigment that converts photons of light into chemical energy. Chlorophyll a mainly absorbs light in the blue (around 430 nm) and red (around 660 nm) parts of the light spectrum, making it essential for photosynthesis.

Its absorption in these specific wavelengths makes it perfectly aligned with what Engelmann's experiment found: the high activity of photosynthesis within the blue and red light bands. Thanks to chlorophyll a, plants can efficiently harness light energy and use it in the conversion of carbon dioxide and water into glucose and oxygen. This pigment is fundamental in the photosynthetic process, setting the stage for energy transformation in plants.

Chlorophyll b

Chlorophyll b acts as an important accessory pigment in photosynthesis. While not as primary as chlorophyll a, it absorbs light energy and passes it to chlorophyll a, extending the range of light wavelengths that a plant can use.

Chlorophyll b absorbs light primarily at wavelengths of 450 nm (blue) and 640 nm (orange/red). This complementary role allows plants to utilize broader spectra of light, enhancing the efficiency of photosynthesis in environments where light quality may not be optimal for chlorophyll a alone. It's this very property that matches the requirements seen in Engelmann's experiment, as both pigments significantly contribute to the action spectrum by absorbing crucial wavelengths necessary for maximal photosynthesis.

Action Spectrum

The action spectrum is a graphical representation that shows the relative effectiveness of different wavelengths of light in fueling photosynthesis. Engelmann's experiment essentially mapped out an action spectrum using oxygen-loving bacteria, illustrating which parts of the spectrum are most effective at driving photosynthesis.

In the action spectrum deduced from Engelmann's findings, red and blue/violet wavelengths were shown to support the highest rates of photosynthesis. These are the wavelengths at which chlorophyll a and chlorophyll b both absorb light efficiently. An action spectrum aids in understanding which wavelengths are absorbed most effectively by the photosynthetic pigments present in a plant, thereby guiding researchers and students alike in their study of how light influences plant growth and energy storage.