Previous-year question practice database
Answer
Exam answer
ADENOSINE DIPHOSPHATE.
Explanation
ADP is adenosine with TWO phosphate groups; ATP is adenosine with THREE. The prefix names the number — DI- two, TRI- three — so the two expansions differ by one word.
THE ENERGY CYCLE in one line: ADP + inorganic phosphate + ENERGY → ATP. Adding the third phosphate STORES energy; removing it RELEASES energy for the cell to use. ATP is therefore called the energy currency of the cell.
In photosynthesis this happens in the LIGHT reaction, where light energy is used to convert ADP into ATP, and the ATP is then spent in the DARK reaction to build glucose.
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