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

What is osmosis?

1. The movement of nutrients into the cell

2. The movement of water from low to high concentration

3. The movement of water from high to low concentration

4. The movement of dissolved gases across a membrane

The correct answer is: The movement of water from high to low concentration

Osmosis is defined as the movement of water molecules across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration. This process occurs in order to balance solute concentrations on both sides of the membrane. When there is a higher concentration of solutes in one area, there will be a correspondingly lower concentration of water. Water will naturally move towards the area of higher solute concentration, which equates to lower water concentration, until equilibrium is reached. Understanding this process is crucial in biological systems as it helps maintain cell turgor, facilitates nutrient absorption, and plays a role in various physiological functions. For example, when plant cells are in a hypotonic solution (where the external environment has a lower concentration of solutes than inside the cell), water enters the cell, making it turgid and providing structural integrity to the plant.