Priestley's Experiments & Plant Gas Exchange — NEET Biology
📚 Practice ConceptJoseph Priestley (1733-1804) in 1770 performed a series of experiments that revealed the essential role of air in the growth of green plants. Priestley, you may recall, discovered oxygen in 1774. Priestley observed that a candle burning in a closed space – a bell jar, soon gets extinguished. Similarly, a mouse would soon suffocate in a closed space. He concluded that a burning candle or an animal that breathe the air, both somehow, damage the air. But when he placed a mint plant in the same bell jar, he found that the mouse stayed alive and the candle continued to burn. Priestley hypothesised as follows: Plants restore to the air whatever breathing animals and burning candles remove.
Arrange the following major discoveries in the understanding of photosynthesis in chronological order from earliest to most recent: A. Demonstration that plants restore the quality of air. B. Proof that sunlight is indispensable for oxygen release by green plant parts. C. Evidence for glucose (starch) formation in plants and location of chlorophyll. D. Description of the first action spectrum of photosynthesis using filamentous algae and bacteria. E. Proposal that oxygen evolved during photosynthesis originates from water. F. Mapping of the pathway of carbon assimilation using C14.
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Correct answer: A — A → B → C → D → E → F
Let's arrange the discoveries chronologically based on NCERT text: A. Joseph Priestley (1770) performed experiments that revealed the essential role of air and hypothesised that plants restore the air. (Page 134) B. Jan Ingenhousz (1730-1799) showed that sunlight is essential for the plant process that purifies the air and that only the green parts release oxygen. (Page 134) C. Julius von Sachs (about 1854) provided evidence for production of glucose (stored as starch) and that chlorophyll is located in special bodies within plant cells. (Page 135) D. T.W. Engelmann (mid-1800s, after Sachs) described the first action spectrum of photosynthesis using Cladophora and aerobic bacteria. (Page 135) E. Cornelius van Niel (early 1900s, after Engelmann) based on his studies of purple and green bacteria, proposed that the O2 evolved by green plants comes from H2O, not from carbon dioxide. (Page 135) F. Melvin Calvin (just after World War II, 1961 Nobel Prize) mapped the pathway of carbon assimilation using C14. (Page 133, 'Melvin Calvin' profile, and page 142) Thus, the correct chronological order is A → B → C → D → E → F.
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