Which one among the following is the source of energy in cells ?  

The correct answer is ATP

Explanation:

• Cells require energy to perform various functions, and this energy is derived from the molecule called Adenosine Triphosphate (ATP).
• ATP serves as the primary energy carrier in cells, providing the necessary power for cellular processes such as muscle contraction, nerve impulse propagation, and chemical synthesis.
• ATP is produced during cellular respiration and photosynthesis and is used by cells to store and transfer energy.
• ATP (Adenosine Triphosphate) is the primary energy carrier in cells. It releases energy when its phosphate bonds are hydrolyzed. This energy is used for various cellular activities. ATP is often referred to as the "energy currency" of the cell because it is readily used to fuel biochemical reactions.

Other Options:

• ADP (Adenosine Diphosphate): This molecule is a lower-energy form of ATP. It is converted to ATP by the addition of a phosphate group during cellular respiration or photosynthesis, thus it is not the direct source of energy but rather a precursor.
• AMP (Adenosine Monophosphate): This molecule contains only one phosphate group and is an even lower-energy form than ADP. It is involved in cellular processes but is not a primary source of energy.
• NAD (Nicotinamide Adenine Dinucleotide): This is a coenzyme involved in redox reactions, carrying electrons from one reaction to another. While it plays a crucial role in energy production pathways like glycolysis and the citric acid cycle, it is not the direct source of energy itself.