The difference between pinocytosis and receptor-mediated endocytosis is that ________.

• A. Pinocytosis brings only water molecules into the cell, receptor-mediated endocytosis brings in other molecules also
• B. Pinocytosis increases the surface area of the plasma membrane, receptor-mediated endocytosis decreases it
• C. Pinocytosis is nonselective, receptor-mediated endocytosis offers more selectivity
• D. Pinocytosis can concentrate substances from the extracellular fluid, receptor-mediated endocytosis cannot

Answer: (C)

Verified step by step guidance

1. Understand the basic definitions: Pinocytosis is a type of endocytosis where the cell ingests extracellular fluid and its dissolved solutes. Receptor-mediated endocytosis is a more specific form of endocytosis where cells absorb metabolites, hormones, proteins – and in some cases viruses – by the inward budding of the plasma membrane vesicles containing proteins with receptor sites specific to the molecules being absorbed.
2. Identify the key difference: Pinocytosis is often referred to as 'cell drinking' and is nonselective, meaning it does not target specific molecules but rather engulfs whatever solutes are present in the extracellular fluid. In contrast, receptor-mediated endocytosis is selective because it involves the binding of specific molecules to receptors on the cell surface before being internalized.
3. Consider the selectivity aspect: Since pinocytosis is nonselective, it does not differentiate between different types of molecules in the extracellular fluid. Receptor-mediated endocytosis, however, is highly selective due to the presence of specific receptors that bind to particular molecules, allowing the cell to concentrate and internalize specific substances.
4. Evaluate the options given: The correct answer should reflect the selectivity difference between the two processes. Pinocytosis being nonselective and receptor-mediated endocytosis offering more selectivity aligns with the definitions and characteristics of these processes.
5. Conclude with the correct choice: Based on the understanding of the processes, the correct answer is that pinocytosis is nonselective, while receptor-mediated endocytosis offers more selectivity, as it involves specific receptors for molecule uptake.