Nursing Entrance Exam (NEX) Practice Exam

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What substance is primarily responsible for carrying energy within cells?

Glucose
ATP
Lactic acid
Actin

The correct answer is: ATP

The substance primarily responsible for carrying energy within cells is ATP, or adenosine triphosphate. ATP acts as the primary energy carrier in all living organisms, providing the energy necessary for various cellular processes. When ATP is hydrolyzed, it releases energy that can be utilized for muscle contraction, active transport, biosynthesis, and other critical cellular functions. Glucose, while an important energy source, undergoes conversion to ATP through metabolic processes like glycolysis and cellular respiration before it can be utilized by the cell. Lactic acid is a byproduct of anaerobic respiration and does not serve as an energy carrier; rather, it indicates the lack of oxygen during energy production. Actin is a protein that plays a role in muscle contraction and cellular structure but does not carry energy itself. Overall, ATP is central to energy transfer in biological systems, making it the correct answer.