Surface ocean waters undergoing high rates of photosynthesis also exhibit (a) da
ID: 487411 • Letter: S
Question
Surface ocean waters undergoing high rates of photosynthesis also exhibit (a) daily increases and nightly decreases in pH. (b) daily decreases and nightly increases in pH. (c) constant pH values from day to night. (d) typically lower pH value than deep ocean water.
What happened on Earth in response to the Great Oxygen Event (circle all that apply) (a) Iron oxides precipitated from solution (b) Superoxide dismutase was created (c) Anaerobes became extinct (d) Mitochondria came into existence.
The proton motive force is used to drive (a) transfer of electrons along the electron transport chain. (b) ADP production using ATP synthase (c) ATP production via substrate level phosphorylation (d) ATP production using ATP synthase.
Explanation / Answer
Ans. 1. Correct option. B. Daily decrease (becomes less acidic or more basic) and nightly increase in pH.
Dissolve CO2 in ocean water form carbonic acid (H2CO3) which further donates a proton to the aqueous medium and increases its pH (makes more acidic).
H2O + CO2 ---------> H2CO3 ----------> H+ + HCO3-
During day time, photoautotroph consume dissolve CO2 through photosynthesis. It causes lowering of CO2 concentration and decrease of pH subsequently, too.
During night time, the photoautotrophs carry out cellular respiration and release CO2 as byproduct, therefore, increase in [CO2] also increase pH in night.
Option. C. Incorrect- pH changes during day and night time.
Option. D. Incorrect. The ocean surface exhibiting photosynthesis reduces [CO2] in water. So photosynthesis makes the pH higher (more alkaline) ; but does not lowers (does not makes more acidic) pH.
Ans. 2. Great oxygen event (GOE) introduced large amount of free O2 into the atmosphere because of photosynthesis by cyanobacteria. Availability of free O2 in atmosphere further led to the evolution of mitochondria- that could carry our aerobic respiration with more efficient energy harvesting pathways.
Option. A. Incorrect. Precipitation of iron oxides did not cause the event. Most of iron ores still often in form of oxides, i.e. do not release free oxygen to atmosphere easily.
B. The enzyme appeared much later after evolution of mitochondria. Moreover, it appeared in certain organisms that evolved for cellular respiration. The word ‘creation’ is not true for evolution of this enzyme after GOE.
Option. C. Anaerobes di not extinct. There are numerous anaerobes still present in the environment.
Ans. 3. D.
Proton motive force generates ATP when H+ flow back into the matrix from inter-membrane space.
Option. A- Incorrect- Proton motive force (PMF) does NOT drive electron transport through ETC. However, the reverse of its is true, i.e. flow of electrons through ETC establishes proton motive force.
Option. B. Incorrect. PMF produces ATP from ADP and Pi. It does not produces ADP.
Option. C. Incorrect. ATP production during glycolysis and TCA is called substrate level phosphorylation because substrate hydrolysis results ATP directly. Substrate level phosphorylation does not requires PMF.
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