Which is broken down during cellular respiration to release energy?
A. ADP
B. Food Molecules
C. Water
The correct answer and explanation is :
The correct answer is B. Food Molecules.
Explanation:
Cellular respiration is a crucial biochemical process that takes place in cells to convert nutrients into usable energy in the form of adenosine triphosphate (ATP). The primary purpose of cellular respiration is to break down food molecules, particularly glucose, and extract energy that is stored within their chemical bonds. This energy is then used by the cell to carry out various functions, including growth, repair, and maintenance.
Food molecules, particularly carbohydrates like glucose, fats, and proteins, are broken down during cellular respiration. The process can be divided into several stages:
- Glycolysis – This is the first stage of cellular respiration and occurs in the cytoplasm. One molecule of glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (three carbon each), producing a small amount of ATP and NADH in the process. Glycolysis does not require oxygen and is considered anaerobic.
- Pyruvate Decarboxylation and Citric Acid Cycle (Krebs Cycle) – The pyruvate molecules from glycolysis are transported into the mitochondria, where they are converted into Acetyl-CoA. This molecule enters the Krebs cycle, where it undergoes a series of reactions, generating NADH, FADH2, and a small amount of ATP, while releasing carbon dioxide as a waste product.
- Electron Transport Chain (ETC) – The NADH and FADH2 produced in the previous stages carry high-energy electrons to the electron transport chain, located in the inner mitochondrial membrane. This is where the majority of ATP is produced. As electrons move through the chain, they help pump protons (H+) across the membrane, creating a proton gradient. The protons then flow back through ATP synthase, driving the production of ATP. Oxygen acts as the final electron acceptor, combining with electrons and protons to form water.
Thus, food molecules such as glucose are the primary source of energy in cellular respiration, and breaking them down releases the energy needed for ATP production. ADP (Adenosine Diphosphate) and water are involved in the process but are not the main substances broken down to release energy.