The conversion of \(\mathrm{CO}_{2}\) into carbohydrates by plants via photosynthesis can be represented by the reaction $$6 \mathrm{CO}_{2}(\mathrm{g})+6 \mathrm{H}_{2} \mathrm{O} \stackrel{\text { light }}{\longrightarrow} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{O}_{2}(\mathrm{g}).$$ To study the mechanism of photosynthesis, algae were grown in water containing \(^{18}\) O, that is, \(\mathrm{H}_{2}^{18} \mathrm{O}\) The oxygen evolved contained oxygen-18 in the same ratio to the other oxygen isotopes as the water in which the reaction was carried out. In another experiment, algae were grown in water containing only \(^{16} \mathrm{O}\),but with oxygen-18 present in the \(\mathrm{CO}_{2}\). The oxygen evolved in this experiment contained no oxygen-18. What conclusion can you draw about the mechanism of photosynthesis from these experiments?

Step by step solution

01

Understanding the problem

The question presents two different experiments, both involving the photosynthesis process using algae. In the first experiment, algae were grown in water containing oxygen-18, and the result was that the oxygen product also contained oxygen-18. In the second experiment, the water contained only oxygen-16, but the carbon dioxide contained oxygen-18. The oxygen produced from this experiment had no traces of oxygen-18.

02

Analyzing the first experiment

In the first experiment, both the reactants - water (H_2^{18}O) and carbon dioxide (CO_{2}) - had the possibility of contributing the oxygen-18 to the product. However, it clearly stated that the ratio of oxygen-18 to the other oxygen isotopes in the product was the same as the ratio in the water used for the reaction. This implies that, in this first experiment, the oxygen-18 in the product came from the water.

03

Analyzing the second experiment

In the second experiment, the water contained only oxygen-16, but carbon dioxide contained oxygen-18. Yet, it was stated that the oxygen produed during this experiment contained no traces of oxygen-18. This means that the oxygen-18 present in the carbon dioxide did not contribute to the oxygen in the final product.

04

Drawing conclusion

The results of these two experiments indicate that the oxygen released during photosynthesis comes from water (H_{2}O) and not from carbon dioxide (CO_{2}). This conclusion is consistent with experimental evidence showing that the oxygen in carbon dioxide is incorporated into glucose (C_{6}H_{12}O_{6}), the other product of photosynthesis, and not released as oxygen gas.

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!