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

What is the function of the cell membrane in animal and plant cells?

1. Supports the cell structure

2. Controls the movement of substances in and out of the cell

3. Acts as a site for photosynthesis

4. Contains the genetic material of the cell

The correct answer is: Controls the movement of substances in and out of the cell

The cell membrane plays a crucial role in maintaining the integrity of both animal and plant cells by acting as a selective barrier. This means its primary function is to control what enters and exits the cell, thereby regulating the internal environment, a process known as homeostasis. The membrane is composed of a lipid bilayer with embedded proteins that facilitate the transport of substances, such as nutrients, ions, and waste products. This selective permeability is vital for processes such as nutrient uptake and waste removal, allowing cells to function optimally. The other options describe functions that are important to cellular structure and activity but do not pertain specifically to the function of the cell membrane. For instance, while the cell wall in plants provides structural support, the cell membrane itself does not perform this role. Similarly, photosynthesis occurs in chloroplasts, not within the cell membrane, and genetic material is housed in the nucleus, making those options inaccurate concerning the cell membrane's function.