Which type of hormones must bind to particular receptors within the cell membrane due to being water soluble?

Non-steroidal hormones are water-soluble and cannot easily cross the lipid bilayer of the cell membrane. Therefore, they must bind to specific receptors located on the cell membrane. This binding triggers a cascade of intracellular events, often involving second messengers like cyclic AMP, which then mediate the hormone's effects on the target cell.

In contrast, steroidal hormones are lipid-soluble and can pass through the cell membrane, allowing them to bind to receptors inside the cell. Thyroid hormones, while they have some characteristics of both steroid and peptide hormones, can also pass through the membrane due to their lipid-soluble nature. Peptide hormones, which are a subset of non-steroidal hormones, also follow the same mechanism as non-steroidal hormones in binding to cell membrane receptors. However, since the question specifically focuses on the broader category of non-steroidal hormones, this is the most appropriate classification.