barrier function

例句：

1. 1. The cell membraneis a natural barrier that protects thecell from external threats.
   细胞膜是一个天然的屏障，保护细胞免受外部威胁。
2. 2. Theimmune system has a barrier function to preventpathogens from entering the body.
   免疫系统具有屏障功能，以防止病原体进入身体。
3. 3. The barrierfunction of the skin helps to keep outharmful substances and microorganisms.
   皮肤的屏障功能有助于防止有害物质和微生物进入体内。