Mass flow is distinguished from diffusion because mass flow is driven by:

1. Both processes move substances, but the driving force differs. 2. Mass flow is bulk movement of substances from one region to another because of a pressure difference. 3. Diffusion is driven instead by a concentration gradient, from high to low. 4. Osmosis is the case requiring a semi-permeable membrane. 5. Responding to a stimulus is irritability, which is a property of living things rather than a transport mechanism. _Source: NECTA CSEE 2022 Biology 033, Question 1: Multiple Choice Items, item (vii)_