The terminal electron acceptor in respiration may be 1) oxygen. 2) nitrate. 3) NAD. 4) an inorganic molecule. 5) oxygen, nitrate AND an inorganic molecule.
The correct answer and explanation is:
The correct answer is 5) oxygen, nitrate AND an inorganic molecule.
In cellular respiration, the terminal electron acceptor is a molecule that accepts electrons at the end of the electron transport chain (ETC). The role of the terminal electron acceptor is crucial for the continuation of the electron transport process, as it helps to prevent the accumulation of electrons, which would halt the entire respiratory process.
- Oxygen is the most common terminal electron acceptor in aerobic respiration. In this process, oxygen combines with electrons and protons to form water. This reaction is highly efficient and is a characteristic feature of aerobic organisms. Oxygen’s high electronegativity allows it to efficiently accept electrons and drive the production of ATP.
- Nitrate can act as a terminal electron acceptor in some microorganisms, particularly in anaerobic conditions. This process is known as nitrate respiration or denitrification. Certain bacteria and archaea that cannot use oxygen as a terminal electron acceptor instead use nitrate (NO₃⁻), reducing it to nitrite (NO₂⁻) or even nitrogen gas (N₂). This allows them to survive in environments with little or no oxygen.
- NAD (Nicotinamide adenine dinucleotide) is not a terminal electron acceptor in respiration. Instead, NAD⁺ functions as an electron carrier. During glycolysis and the citric acid cycle, NAD⁺ accepts electrons and becomes NADH. This NADH is then used in the electron transport chain to donate electrons, rather than accepting them at the terminal end.
- An inorganic molecule other than oxygen or nitrate can also serve as a terminal electron acceptor in certain anaerobic environments. Examples include sulfate (SO₄²⁻) and carbon dioxide (CO₂), which can be reduced to hydrogen sulfide (H₂S) or methane (CH₄), respectively, in processes like sulfate reduction or methanogenesis.
Thus, oxygen, nitrate, and other inorganic molecules can all serve as terminal electron acceptors in various types of respiration, depending on the organism and the environmental conditions.