Marie and calvin dissolved 10 grams of kno3 in 100 grams of water at 25oc. next they added 5 grams more. calvin told marie that they could continue to add solute until they reached 40 grams because the solution was still

Hello!

Calvin told Marie that they could continue to add solute until the reached 40 grams because the solution was still unsaturated.

Unsaturated solutions are those in which the solvent (in this case water) can still dissolve more solute (in this case KNO₃) at the given pressure and temperature. This can be seen visually when adding more solute doesn't result in the presence of grains of solids that settle in the bottom of the flask. That happens because the rate of dissolving is higher than the rate of crystallization. 

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The succinate dehydrogenase catalyses the oxidation of succinate into fumarate in the Krebs cycle  derived electrons being fed to the respiratory chain complex III to reduce oxygen and form water