Each miner can determine whether there is no transaction in a block. The number of transactions in a single block is not the same as the higher level of computational power required to solve the block.
After receiving a new transaction information, a node must verify it; Especially the transaction has to be sure that no input has been spent before. Then, the nodes needed to access the blockchain are also to be checked. If a user can not rely on the neighbors of his network, then he must keep a full copy of the blockchain, as any input can be verified.
As the white paper in Nakamatu is written - it is possible to verify Bitcoin payment (which is called simplified payment verification) without a full network node. In this process, a user's longest chain block headers require only a copy - to find network nodes until they get the longest chain. The mercklays branch is then connected to the fixed block by linking it. In relation to linking the transaction in the chain, it is understood that the network node has accepted it, and the added blocks further guarantee it.
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