A Level Biology Practice Exam

What is a defining characteristic of a mass transport system?

1. Transport of substances through diffusion

2. A transport system that moves substances individually

3. A transport system where substances are transported in a mass of fluid

4. Transport of gases only

The correct answer is: A transport system where substances are transported in a mass of fluid

A defining characteristic of a mass transport system is that substances are transported in a mass of fluid. This means that the movement of materials occurs collectively within a fluid medium, facilitating the efficient distribution of nutrients, gases, and waste products throughout an organism. In mass transport systems, such as the circulatory system in animals or the xylem and phloem in plants, the fluid carries various substances simultaneously. This contrasts with transport mechanisms like diffusion, where substances move independently down their concentration gradient, which is less efficient for large distances or larger volumes. Additionally, mass transport systems enable the rapid movement of substances, supporting the metabolic needs of the organism more effectively than individual transport alone. Furthermore, the scope of mass transport systems is not limited to gases only; they also transport nutrients and waste, illustrating their broader functional role in biological systems. Therefore, the correct answer highlights the collective transportation aspect inherent to mass transport mechanisms.