Which of the following transport processes across a cell membrane does not require energy (ATP) from the cell?

Introduction / Context:
Cells must move water, ions, gases, and nutrients across their membranes to stay alive. Some of these movements require direct energy expenditure in the form of ATP, while others occur passively due to natural concentration differences. Distinguishing between passive and active transport processes is a core concept in cell biology and physiology. This question focuses on which processes do not require energy from the cell and therefore are classified as passive transport.

Given Data / Assumptions:
• The processes listed are osmosis, diffusion, both together, and active transport mechanisms. • Energy refers to direct usage of cellular ATP. • Normal biological conditions and definitions are assumed.

Concept / Approach:
Diffusion is the passive movement of particles from a region of higher concentration to a region of lower concentration. Osmosis is a special case of diffusion that involves the movement of water through a selectively permeable membrane from lower solute concentration to higher solute concentration. Both processes occur due to the kinetic energy of molecules and do not require ATP from the cell. In contrast, active transport moves substances against their concentration gradient and always requires ATP. Therefore, both osmosis and diffusion fall into the category of energy independent, passive processes.

Step-by-Step Solution:
Step 1: Define diffusion as passive movement down a concentration gradient. Step 2: Define osmosis as diffusion of water through a selectively permeable membrane. Step 3: Note that neither process uses ATP; they are driven by natural particle motion and concentration differences. Step 4: Recall that active transport is the movement of substances against their gradient and requires ATP. Step 5: Choose the option that groups osmosis and diffusion together as processes that do not require cellular energy.

Verification / Alternative check:
In daily life and in laboratory demonstrations, diffusion and osmosis occur spontaneously without any external energy input. For example, perfume spreading in a room or water entering plant root hairs by osmosis are natural passive processes. On the other hand, the sodium potassium pump in nerve cells uses ATP with each cycle, clearly representing active transport. These examples confirm that both simple diffusion and osmosis are passive and do not require direct ATP use by the cell.

Why Other Options Are Wrong:
Option A (Osmosis only) is incomplete because diffusion of solutes is also a passive, energy independent process. Option B (Diffusion only) is incomplete because water movement by osmosis is also passive and energy free. Option D (Active transport processes) is incorrect because active transport by definition requires ATP to move substances against their concentration gradients.

Common Pitfalls:
Students sometimes think that any movement across a membrane must require ATP, which is not true. Another error is to treat osmosis as a completely different category unrelated to diffusion, even though it is simply diffusion of water. Remember that passive processes like diffusion and osmosis rely on the inherent kinetic energy of molecules and do not consume cellular ATP, whereas active transport does.

Final Answer:
The transport processes that do not require cellular energy are both osmosis and diffusion.