What is the relationship between $CO_2$ concentration and the rate of respiration?

The three boxes in this diagram represent the three major biosynthetic pathways in aerobic respiration. Arrows represent net reactants or products. Arrows numbered $4, 8$ and $12$ can all be

......... is the result of respiration.

Select the correct option to complete the following statements:
$(1)$ The $TCA$ cycle begins with the condensation of $OAA$ and water with $Acetyl-CoA$ to yield $Citric$ $acid$.
$(2)$ In fermentation,yeast converts glucose into ethanol under $Anaerobic$ conditions.

Select the correct option:
$(1)$ Fermentation / Aerobic respiration does not have an electron transport system.
$(2)$ Combustion / Respiration is a biochemical process.

How many $ATP$ molecules are produced via substrate-level phosphorylation during the complete oxidation of one glucose molecule in aerobic respiration?