Discussion
In the history of photosynthetic research, the empirical reaction of photosynthesis was first proposed for green plants (equation 1), followed by another reaction for purple sulfur bacteria (equation 2), leading to a generalized equation for photosynthesis (equation 3)
CO2 + H2O \(\xrightarrow{\text{light}}\) (CH2O) + O2 (equation 1)
CO2 + 2H2S \(\xrightarrow{\text{light}}\) (CH2O) + H2O + 2S (equation 2)
CO2 + 2H2A \(\xrightarrow{\text{light}}\) (CH2O) + H2O + 2A (equation 3)
where H2A in equation 3 is a generalized electron donor.
Which one of the following statements is DISPROVEN by equation 3?
Answer: A
The statement disproven is The source of oxygen produced in photosynthesis in green plants is CO2.
Van Niel's comparison is the point of the question. Purple sulfur bacteria use H2S and release sulfur, not oxygen, while green plants use H2O and release oxygen. Writing both as one general reaction, with H2A as the electron donor and 2A as its oxidised product, places the released element (S or O) in the donor, not in CO2. For green plants A is oxygen, so the O2 must come from water, a conclusion later confirmed with 18O-labelled water.
That supports, rather than disproves, the statement that the oxygen comes from H2O. Every equation includes light, so the light statement is consistent with them. The equations write the product as the generic (CH2O) and say nothing either way about glucose.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development