Expert: Walter Hintz - 4/13/2009

Question
QUESTION: Hello! long & interesting question..I carried out an experiment to measure the rate of photosynthesis( by accumulation of O2) in a hydrilla plant using 4 beakers - 1 which had dilute HCl instead of water, another with dil H2S04, another with dil NaOH, and the last one with water. What according to you should the change in rate of photosynthesis be in the various beakers? I got the foll results: The fall in water level (rise in O2 level in test tube) in 1hr was maximum in dil. HCl, then water, then h2so4, then NaOH (least).. however, later the acidic ones died(shown by loss of greenness).. is it correct if said that HCl temporarily inc rate of photosynthesis? if so, what is d reason (is it Cl- ions?) Besides, the size of the plants were not exactly the same - could this have significantly affected the amt of O2 evolved in testtube which represents rate of photosynthesis?

ANSWER: It looks like you carried out your study  well except for the difference in the size of the plants.  If the difference in size was great the photosynthetic rate could be effected. If your result showed increased rate with HCl and if you repeat the test and get the same results then you can safely conclude that HCl was a factor.  I believe that the hydrogen ino concentration would the reason not the Cl+

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QUESTION: Thanks a lot for the answer. The diff in size of plants was not great - around 10 -15% variation max, but in the result - hcl water level fell by 4mm, water 2mm, h2so4 1mm, naoh 0.4mm. the exp was not repeated due to time constraints, but sunlight, and other factors were same for each beaker..
1. Could u tell me / link me to the cause of Hcl improving photosysntheseis temporarily - if it was H+ ions then why didnt it increases in H2SO4 which produces 2 H+ ions for every molecule? this link :  http://pubs.acs.org/doi/abs/10.1021/bi026175y talks about The Function of the Chloride Ion in Photosynthetic Oxygen Evolution, but i didnt understand whether it indicates that more Cl- ions will inc photosynthesis or not.. pls read & get back if u can
2. will this experiment, if the results are accepted, allow me to conclude a relationship between pH and rate of photosynthesis?
3. Theoretically does such a relationship exist - could u guide me to some websites/ information on this?
thanks again.. in advance

Answer
All chemical reactions including photo synthesis depend upon enzymes and enzymes operate within certain pH ranges. That is why I suggested H+ as the factor increasing the rate rather then Cl-
 Why the sulfuric acid did not cause an increase I do not know but the results show that it not.  It must have to do with the chemistry.
Apprently a lack of Cl- slows dowh O2 production but the article does not explain why as far as I can tell to