This takes place when molecules diffuse across the cell membrane by travelling through specific transport proteins. It occurs down a concentration gradient - molecules move from an area of high to ...

Transport of molecules within a cell and out of the cell requires a complex endomembrane system. Endocytosis occurs when the cell membrane engulfs particles (dark blue) outside the cell ...

Transport across membranes All cells are enclosed by a cell membrane, which is selectively permeable. Molecules can move into or out of cells by diffusion and active transport. Cells can gain or ...