Answer:

20.A

21.B

22.B or C

23.C

24.A

Explanation:

20.The matrix contains the deoxyribonucleic acid (DNA) of the mitochondrial genome and the enzymes of the tricarboxylic acid (TCA) cycle (also known as the citric acid cycle, or Krebs cycle), which metabolizes nutrients into by-products the mitochondrion can use for energy production.

21.The Krebs cycle itself actually begins when acetyl-CoA combines with a four-carbon molecule called OAA (oxaloacetate) (see Figure above). This produces citric acid, which has six carbonatoms. This is why the Krebs cycle is also called the citric acid cycle

22.For every pair of electrons transported to the electron transport chain by a molecule of NADH, between 2 and 3 ATP are generated.

23.ATP synthase is the enzyme that makes ATP by chemiosmosis. It allows protons to pass through the membrane and uses the free energy difference to phosphorylate adenosine diphosphate (ADP), making ATP.

24.Work on mitochondria did not stop in the 1950s after it was named “the powerhouse of the cell.” Subsequent studies throughout the rest of the 20th century identified the mitochondria as an incredibly dynamic organelle involved in multiple cellular processes in addition to energy production