Assertion (A) is correct because FSH, or follicle-stimulating hormone, is a peptide hormone that does not enter the target cell. Instead, it interacts with membrane-bound receptors on the surface of the target cell. This is a common feature of peptide hormones, as they are too large and hydrophilic to pass through the cell membrane.

Reason (R) is also correct. When FSH binds to its receptor, it triggers a cascade of intracellular events, including the production of second messengers like cyclic AMP (cAMP). The second messengers then go on to activate various biochemical and physiological responses within the target cell, such as cell growth and hormone production. This is a typical process for signal transduction initiated by the binding of a hormone to its cell surface receptor.

However, (R) is not the correct explanation of (A) because it doesn't directly address why FSH doesn't enter the target cell. The reason FSH does not enter the target cell is that it is a peptide hormone, which cannot cross the cell membrane. Instead, it interacts with cell surface receptors to initiate a signaling cascade. The generation of second messengers, like cAMP, is a part of the signaling process that takes place after FSH binds to its receptor, but it is not the reason why FSH doesn't enter the cell.