merkle tree – How/where is the informatioin regarding the mapping of a transaction to a particular block stored?

According to the bitcoin white paper a block contains Previous Hash, Nonce and Root Hash. The root hash is a merkle tree root node of all the transactions that have been confirmed to that particular block.

I read here in the fifth paragraph of the top answer that “a transaction that claims to have been from block #234133 we can get the transactions for that block, verify the Merkle tree, and know that the transaction is valid.”

So say a block m somewhere in the blockchain holds n transactions. Where and how is the mapping of a particular set of transaction to a particular block stored? Because the blockchain itself only contains the root hash of all transactions to save space. So are there other hidden components that haven’t been published in the white paper and are there resources to get a comprehensive idea about them?