正确

错误

正确

错误

对峙反应

基元反应

平行反应

连续反应

冲突域

广播域

管理域

控制域

平行反应的总反应

对峙反应的总反应

连串反应的总反应

基元反应

定性分析

定量分析

结构分析

化学分析

The length of time a cell takes to respond to an extracellular signal can vary greatly, depending on what needs to happen once the message has been received.

Some extracellular signals act swiftly: acetylcholine can stimulate a skeletal muscle cell to contract within milliseconds and a salivary gland cell to secrete within a minute or so. Such rapid responses are possible because, in each case, the signal affects the activity of proteins that are already present inside the target cell, awaiting their marching orders.

Other responses take more time. Cell growth and cell division, when triggered by the appropriate signal molecules, can take many hours to execute.

This is because the response to these extracellular signals requires changes in gene expression and the production of new proteins.