2.5.1 Passive transport involves diffusion

1 molecules may move randomly

a lot of molecules move directionally → dynamic equilibrium动态平衡

Passive transport: diffusion of a substance across a biological membrane

Passive transport is classified into 2 types: (both follows the concentration gradient)

1. Simple diffusion: free
2. Facilitated diffusion协助扩散: with the help of channel protein/carrier protein

Channel proteins let specific molecules to pass (not so specified) eg. Aqua porins水通道蛋白

Carrier proteins bind with molecules and shuttle them across the membrane (specified)

2.5.2 Active transport requires energy

Moves from low concentration to high concentration, consumes ATP

1. Primary active transport uses the chemical energy stored in ATP

初级主动运输 eg. Sodium potassium pump, proton pump

1. Secondary active transport uses the energy stored in an electrochemical gradient(电化学梯度)

次级主动运输 用初级主动运输产生的电化学梯度进行运输

conduct in same direction is symport, different direction is anti port

1. Co-transport 协同转运

2.5.3 Endocytosis & exocytosis move large molecules into/out of a cell