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

What happens to red blood cells when they become turgid?

1. They become more flexible

2. They burst due to increased pressure

3. They shrink in size

4. They strengthen their membrane

The correct answer is: They burst due to increased pressure

When red blood cells become turgid, they are subjected to an influx of water, resulting in increased internal pressure. This condition arises when the cells are in a hypotonic environment, meaning that the concentration of solutes outside the cell is lower than that inside. Consequently, water moves into the cells by osmosis. As the cell takes in more water, the pressure builds up within it. If this pressure becomes excessive, the cell membrane can no longer withstand it, leading to the rupture or bursting of the cell. This phenomenon explains why the correct answer is that the cells burst due to increased pressure. Understanding this process also highlights the importance of maintaining osmotic balance in red blood cells. If placed in a hypertonic solution, the opposite occurs — water would move out of the cell, causing it to shrink. The nature and structure of the red blood cell membrane, while flexible, cannot endure unlimited expansion without compromising their integrity, which is pivotal for their function in transporting oxygen throughout the body.