Which of the following is most likely to have a much higher breathing rate?

The mechanism of the human body which facilitates the exchange of respiratory gases is called:

“All plants give out oxygen during day and carbon dioxide during night”. Do you agree with this statement? Give reason.

After a vigorous exercise,you may experience cramps in your leg muscles. Why does this happen?

In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by a set of reactions where pyruvic acid is converted to $CO_2$ and ethanol. The enzymes, pyruvic acid decarboxylase and alcohol dehydrogenase, catalyse these reactions. Answer the following questions:
$(i)$ Write the chemical equation for alcoholic fermentation.
(ii) $A$ test tube containing molasses solution and yeast is kept in a warm place overnight. What gas is collected from the mixture?
(iii) How does ethyl alcohol fermentation occur?
(iv) What is pyruvic acid?

Why must the respiratory surface of animals always be moist?