CK12 Life Science

Table 4.2:An Overview of the Citric Acid Cycle

Inputs Outputs

2 two-carbon molecules 4 CO 2

6 NAD+ 6 NADH (electron carrier)

2 FAD+ 2 FADH 2 (electron carrier)

2 ADP 2 ATP (energy)

Figure 4.13: During electron transport, electrons from glucose (carried by NADH and
FADH 2 ) are passed along until they are finally combined with oxygen, which with the ad-
dition of hydrogen ions, becomes water. Meanwhile, hydrogen ions are pumped across the
cristae of the mitochondria, forming a gradient, and ATP synthase uses the energy of the
movement of hydrogen ions back across the membrane, from high to low concentration, to
make ATP. ( 8 )

Fermentation

Sometimes cellular respiration isanaerobic, occurring in the absence of oxygen. In the
process offermentation,the NAD+is recycled so that is can be reused in the glycolysis
process. No additional ATP is produced during fermentation, so the organism only obtains
the two net ATP molecules per glucose from glycolysis.

Yeasts (single-celled eukaryotic organisms) carry onalcoholic fermentationin the absence
of oxygen, making ethyl alcohol (drinking alcohol) and carbon dioxide. Alcoholic fermenta-