Photosynthesis in plants can be represented by the following overall equation: $$6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \stackrel{\text { Light }}{\longrightarrow} C_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s)+6 \mathrm{O}_{2}(g)$$ Algae grown in water containing some \(^{18} \mathrm{O}\) (in \(\mathrm{H}_{2}^{18} \mathrm{O}\) ) evolve oxygen gas with the same isotopic composition as the oxygen in the water. When algae growing in water containing only \(^{16} \mathrm{O}\) were furnished carbon dioxide containing \(^{18} \mathrm{O},\) no \(^{18} \mathrm{O}\) was found to be evolved from the oxygen gas produced. What conclusions about photosynthesis can be drawn from these experiments?

Step by step solution

01

Review the Photosynthesis Equation

Begin by reviewing the overall equation for photosynthesis: $6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l) \stackrel{\text { Light }}{\longrightarrow} C_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s)+6 \mathrm{O}_{2}(g)$ This equation shows that 6 water molecules and 6 carbon dioxide molecules react to form one glucose molecule and 6 oxygen molecules. From this equation, we will analyze the results of the two experiments provided.

02

Analyze the First Experiment

Experiment 1 states that algae grown in water containing some \(^{18}O\) (in \(H_2^{18}O\)) evolve oxygen gas with the same isotopic composition as the oxygen in the water. This indicates that the oxygen produced during photosynthesis in this experiment comes from the water molecules.

03

Analyze the Second Experiment

Experiment 2 states that when algae growing in water containing only \(^{16}O\) were furnished carbon dioxide containing \(^{18}O\), no \(^{18}O\) was found to be evolved from the oxygen gas produced. This means that despite the presence of \(^{18}O\) in the carbon dioxide provided, the oxygen released during photosynthesis did not contain \(^{18}O\). This suggests that the oxygen produced during photosynthesis in this experiment did not come from carbon dioxide.

04

Draw Conclusions About Photosynthesis

Based on the analysis of the two experiments, we can conclude the following: The oxygen produced during photosynthesis primarily comes from the water molecules and not from the carbon dioxide molecules. This is evident from the fact that the isotopic composition of the oxygen produced in Experiment 1 matches the isotopic composition of the oxygen in the water, while in Experiment 2, the isotopic composition of the oxygen produced did not match the isotopic composition of the oxygen in the provided carbon dioxide. This indicates that the water molecules play a more significant role in contributing the oxygen released during photosynthesis.

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