The difference between pinocytosis and receptor-mediated endocytosis is that:

• A. pinocytosis transports large solid particles, whereas receptor-mediated endocytosis transports only gases.
• B. receptor-mediated endocytosis only occurs in plant cells, while pinocytosis occurs in animal cells.
• C. pinocytosis engulfs extracellular fluid nonspecifically, while receptor-mediated endocytosis involves the selective uptake of specific molecules via cell surface receptors.
• D. pinocytosis requires energy, but receptor-mediated endocytosis does not.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the two processes being compared: Pinocytosis and Receptor-Mediated Endocytosis. Both are forms of endocytosis, a process where cells engulf substances from their external environment into vesicles for internal use.
2. Step 2: Pinocytosis is often referred to as 'cell drinking.' It involves the nonspecific uptake of extracellular fluid and dissolved solutes into small vesicles. This process does not target specific molecules but rather engulfs whatever is in the surrounding fluid.
3. Step 3: Receptor-mediated endocytosis, on the other hand, is a highly selective process. It involves the use of specific cell surface receptors that bind to particular molecules (ligands) such as hormones, nutrients, or proteins. Once the receptors bind to their target molecules, the cell membrane invaginates to form a vesicle containing the bound molecules.
4. Step 4: Both processes require energy in the form of ATP, as they involve active transport mechanisms. This means that the statement 'pinocytosis requires energy, but receptor-mediated endocytosis does not' is incorrect.
5. Step 5: The correct distinction is that pinocytosis is nonspecific and engulfs extracellular fluid, while receptor-mediated endocytosis is selective and involves specific receptors for targeted molecule uptake. This aligns with the correct answer provided in the problem.