Final answer:
Cellular responses are complex in multicellular organisms due to the variety of cell types with different protein expressions, intricate signaling pathways, and the need for signal integration to ensure coordinated function.
Step-by-step explanation:
Cellular responses are not simple because multicellular organisms are complex and have a variety of different cell types, each with unique responses based on their protein expression. Additionally, these organisms require intricate signaling pathways that involve signal integration, where multiple signals from different cell-surface receptors can converge to activate the same cellular response. This complexity ensures that cells within an organism react appropriately to a diverse range of environmental stimuli and maintain coordinated function across various organs and systems.
In multicellular organisms, cellular responses to the same ligands can differ significantly due to distinct protein expressions in the cells. Furthermore, signaling pathways often interplay with one another, leading a single pathway to diverge towards various endpoints. This is necessary for the organism to appropriately respond to multiple external requirements before committing to a specific response.