A Level Biology Practice Exam 2026 – 400 Free Practice Questions to Pass the Exam

The correct answer highlights the fundamental nature of passive transport in cellular biology. Passive transport is the movement of substances across a cell membrane without the need for energy input from ATP. This process occurs down a concentration gradient, meaning substances move from areas of higher concentration to areas of lower concentration until equilibrium is reached.

During passive transport, molecules such as oxygen, carbon dioxide, and certain ions can freely diffuse through the lipid bilayer or pass through channel proteins. This mechanism is crucial for maintaining homeostasis within the cell, as it allows essential nutrients to enter and waste products to exit effectively without expending cellular energy.

Other options misinterpret the function and consequences of passive transport. It does not increase the cell's energy reserves as it does not require energy; nor is it involved in actively exchanging ions, which characterizes active transport. Additionally, passive transport is not directly linked to cell death; instead, it plays a vital role in sustaining life by regulating the internal environment of the cell.