5. The simplest form of the summary equation for photosynthesis is: CO2 + H2O ?
ID: 274425 • Letter: 5
Question
5. The simplest form of the summary equation for photosynthesis is: CO2 + H2O ? CH2O + O2 What is the advantage of writing the equation in this form? 6. In the 1930s C. B. van Niel hypothesized that the oxygen released during photosynthesis originated from water and not carbon dioxide. Nearly 20 years later scientists tested his hypothesis by performing two experiments. In the first experiment scientists labe water with dioxide with the heavy oxygen. led heavy oxygen (18o). In the second experiment the scientists labeled carbon co, + 2 H2O ? CH20 + 02 + H2O If the oxygen does originate from water, in what products would the heavy oxygen from experiment 1 appear? If the oxygen does originate from water, in what products would the heavy oxygen from experiment 2 appear?Explanation / Answer
5. CH2O is the general form of sugar. This carbohydrate is the building block of long chain molecule such as starch. Thus, the advantage of showing the generalized equation is that it indicates that carbon dioxide and water is converted to carbohydrate and oxygen is liberated. It does not identify what the carbohydrate is. A number of conclusions can be made from this equation:
a) Photosynthesis is a redox reaction, wherein CO2 is reduced to a carbohydrate (CH2O) and water is oxidized to oxygen.
b) The electrons required for the reduction of CO2 is provided by water. In this process, oxygen is released as a byproduct.
The simplest form also does not require any balancing of C, H, and O atoms. In the equation wherein the CH2O is substituted by chemical formula for glucose, the equation needs to be balanced for the number of C, H, and O atoms.
2. The hypothesis of Cornelius van Neil that oxygen in photosynthesis originated from water, was proven by Samuel Ruben, Martin Kaman, and James Logan-Hyde. The van Niel hypothesis was based on the production of sulfur from hydrogen sulfite by purple bacteria that do not release oxygen during photosynthesis.
Ruben et al used heavy isotope of oxygen (18O) for their experiments.
a) In experiment 1, plants were fed with Water labeled with heavy oxygen and carbon dioxide that was unlabelled. It was observed that oxygen that was released by the plants was labeled with 18O.
Right answer: Oxygen released by the plant.
b) In experiment 2, plants were fed with carbon dioxide with labeled oxygen and unlabeled water. However, the oxygen liberated did not have 18O. The carbohydrate formed (glucose) and water formed as products would be labeled with 18O.
Right answer: Carbohydrate (CH2O) and water (H2O) produced by the plant.
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