A Level Biology Practice Exam

What is bulk transport in cellular biology?

1. A passive process of moving small molecules across membranes

2. A form of active transport for large molecules or cells

3. A method for transporting oxygen in the bloodstream

4. A cellular process for nutrient absorption

The correct answer is: A form of active transport for large molecules or cells

Bulk transport in cellular biology refers to the mechanism by which large molecules, particles, or even cells are moved across a cell membrane. This process is distinct from simpler forms of transport such as diffusion or facilitated diffusion, which primarily handle smaller molecules. In bulk transport, energy is required to move substances against their concentration gradient, which classifies it as an active transport process. There are two main types of bulk transport: endocytosis, which involves the cell membrane engulfing material to bring it into the cell, and exocytosis, which releases material from the cell. This is essential for various cellular functions, such as the uptake of nutrients that are too large to enter by conventional means and the removal of cellular waste. The other options describe processes that do not encapsulate the definition of bulk transport accurately. Small molecules typically move through passive processes like diffusion, while transporting oxygen is a physiological process that occurs mainly through red blood cells rather than via bulk transport mechanisms. Nutrient absorption usually happens at the molecular level and does not rely on bulk transport for smaller nutrient molecules.