OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is the first step of diffusion?

1. Particles move from lower to higher concentration

2. Particles move in a linear fashion

3. Particles move randomly from higher to lower concentration

4. Particles only move in specific directions

The correct answer is: Particles move randomly from higher to lower concentration

The first step of diffusion involves particles moving randomly from areas of higher concentration to areas of lower concentration. This process occurs as a result of the natural kinetic energy of particles, causing them to move and collide with one another. When there is a concentration gradient, where one area has a higher concentration of particles than another, the particles will spontaneously spread out to achieve equilibrium. This movement continues until the concentration of particles is uniform throughout the space. Understanding this fundamental concept is essential, as it explains how substances such as gases and nutrients move across cell membranes and within various environments. The other choices do not accurately represent the process of diffusion. Movement from lower to higher concentration contradicts the natural tendency of particles to spread out. Additionally, indicating that particles move in a linear fashion or only in specific directions does not capture the random nature of their motion.