Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

Which structure is a thin layer surrounding the cytoplasm of a cell?

1. Golgi Apparatus

2. Cell Membrane

3. Pili

4. Nucleus

The correct answer is: Cell Membrane

The cell membrane is indeed a thin layer surrounding the cytoplasm of a cell, often referred to as the plasma membrane. It serves as an essential barrier, regulating what enters and exits the cell, thereby maintaining homeostasis. The structure of the cell membrane is primarily composed of a phospholipid bilayer, which allows for the selective permeability essential for cellular function. This membrane not only provides a physical boundary for the cell but also contains proteins that are involved in signaling and transport processes. In contrast, other options refer to different cellular structures that play distinct roles. The Golgi apparatus is involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. Pili are hair-like projections that typically help in adhesion and sometimes motility in bacterial cells, and the nucleus is the organelle that houses the genetic material (DNA) of eukaryotic cells, rather than being a boundary structure.