The correct answer to the multiple-choice question is:
B. phosphate
Cellular respiration is the process by which cells break down glucose molecules to generate energy in the form of adenosine triphosphate (ATP). During cellular respiration, phosphate groups are added to adenosine diphosphate (ADP) to form ATP. This process, known as phosphorylation, occurs in the mitochondria of cells and is a key step in energy production.
Here's a breakdown of the process:
1. Glucose is broken down in the cytoplasm through a series of reactions to produce pyruvate during glycolysis.
2. Pyruvate is transported into the mitochondria where it undergoes further breakdown in the citric acid cycle to generate electron carriers (NADH and FADH2).
3. The electron carriers donate their electrons to the electron transport chain, which pumps protons across the inner mitochondrial membrane, creating a proton gradient.
4. The flow of protons back across the membrane drives the enzyme ATP synthase to phosphorylate ADP by adding phosphate groups, forming ATP.
Therefore, in the context of cellular respiration, phosphate is added to ADP to produce ATP, providing the cell with the energy it needs to carry out various functions.
