biological clock
noun [ C ] uk/baɪ.əˌlɒdʒ.ɪ.kəl ˈklɒk/ us/baɪ.əˌlɑː.dʒɪ.kəl ˈklɑːk/
生物钟；生理钟
your body's natural habit of sleeping, eating, growing, etc. at particular times
Long-haul flights can seriously disrupt your biological clock. 长途飞行可能会严重扰乱你的生物钟。
Idiom
someone's biological clock is ticking idiom informal 生物钟开始滴答作响（指女人担心自己很快就会年龄太大不宜生育）
When a woman says her biological clock is ticking, she means that she is worried that she is getting too old to have a baby.