A compound formed in all living cells and play a key role in energy transformations is known as:

Question

Accepted Answer

The correct option is (3):
Adenosine triphosphate (ATP) is accurately known as the universal energy currency of all living cells—both prokaryotic and eukaryotic. It is a nucleoside triphosphate that is central to bioenergetics, acting as the primary molecule for storing and transferring energy to power nearly all cellular processes. The fundamental energy transformation involves the hydrolysis of ATP, where the bond connecting the outermost phosphate group is cleaved. This reaction converts ATP into Adenosine diphosphate (ADP) and an inorganic phosphate group, and simultaneously releases a large, usable amount of energy. The cell uses this released energy to drive essential functions such as muscle contraction, active transport across membranes, and the synthesis of proteins and nucleic acids, confirming its key role in metabolic energy transformations.

The incorrect option is (1):
Granum is a structural term that refers to a stack of thylakoid discs found within the chloroplasts of photosynthetic cells. It is not a compound and is not present in all living cells, as it is absent in animal cells, fungi, and most bacteria. While the granum is the site where the initial light-dependent energy conversion takes place during photosynthesis (producing some ATP), it is an anatomical feature, not the final, mobile chemical compound that distributes and directly transfers energy for universal cellular work.

The incorrect option is (2):
Adenosine diphosphate (ADP) is a precursor to ATP and a product of ATP's energy release. When ATP powers a reaction and loses a phosphate group, it becomes ADP. Therefore, while ADP is critically involved in the energy cycle, it represents the lower-energy form, or the "discharged battery," that must be re-phosphorylated back into ATP to carry the energy again. It is the ATP molecule, with its high-energy bond, that is the primary compound *known* for playing the key role in *transferring* the energy.

The incorrect option is (4):
Chlorophyll is a green pigment essential for photosynthesis, and its primary function is to capture light energy. It is only found in photosynthetic organisms like plants, algae, and certain bacteria, meaning it is not present in all living cells. Since its role is light absorption and initiating the energy conversion chain, and it is not universally present, it does not fit the description of the compound that is "formed in all living cells" and plays the key role in the final energy transfer steps.