Which of the following is the most immediate source of energy for making most of the ATP in your cells?
a. The transfer of from intermediate substrates to ADP
b. The movement of H⁺ across a membrane down its concentration gradient
c. The splitting of glucose into two molecules of pyruvate
d. Electrons moving through the electron transport chain

Verified step by step guidance

1. Understand the context of ATP production in cells: ATP is primarily synthesized during cellular respiration, which includes glycolysis, the citric acid cycle, and oxidative phosphorylation.
2. Recall that oxidative phosphorylation is the stage where most ATP is produced. This process involves the electron transport chain and chemiosmosis.
3. Recognize that the electron transport chain creates a proton (H⁺) gradient across the inner mitochondrial membrane by pumping H⁺ ions into the intermembrane space.
4. Understand that the movement of H⁺ ions back across the membrane, down their concentration gradient, through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate (Pi).
5. Match the correct option to the explanation: The movement of H⁺ ions across a membrane down their concentration gradient (option b) is the most immediate source of energy for making most of the ATP in cells.

Key Concepts

ATP Synthesis

ATP (adenosine triphosphate) is the primary energy carrier in cells. It is produced through various metabolic pathways, with the most significant being oxidative phosphorylation, where ATP is generated as electrons are transferred through the electron transport chain, ultimately leading to the phosphorylation of ADP.

Proton Gradient

A proton gradient is created when protons (H+) are pumped across a membrane, establishing a difference in concentration. This gradient is crucial for ATP synthesis, as protons flow back across the membrane through ATP synthase, driving the conversion of ADP to ATP, a process known as chemiosmosis.

Glycolysis

Glycolysis is the metabolic pathway that breaks down glucose into pyruvate, producing a small amount of ATP and NADH in the process. While it is an important step in cellular respiration, it is not the most immediate source of ATP compared to the processes that utilize the proton gradient.