One scientist cultured Cladophora in a suspension of Azotobacter and illuminated the culture by splitting light through a prism. He observed that bacteria accumulated mainly in the region of:
Answer: (D) Blue and red light. This is Engelmann's classic action-spectrum experiment: a green alga (Cladophora) in a suspension of aerobic bacteria was illuminated with prism-split light, the bacteria serving as detectors of O2 evolution.
- A.Violet and green light
- B.Indigo and green light
- C.Orange and yellow light
- D.Blue and red light✓
Correct Answer
(D) Blue and red light
Solution & Explanation
This is Engelmann's classic action-spectrum experiment: a green alga (Cladophora) in a suspension of aerobic bacteria was illuminated with prism-split light, the bacteria serving as detectors of O2 evolution. The bacteria accumulated mainly in the blue and red regions of the spectrum, where chlorophyll absorbs most strongly and photosynthesis (O2 release) is maximal. Hence the answer is blue and red light. NCERT: Class 11 Ch 11, p.135 [135:013]: "the bacteria accumulated mainly in the region"