cell membranes restrict diffusion of highly charged molecules, such as ions, and large molecules, such as sugars and amino acids. The passage of these molecules relies on specific transport ...

This takes place when molecules diffuse across the cell membrane by travelling through specific transport proteins ... require a supply of energy because diffusion is a spontaneous process.

In both single-celled organisms like prokaryotic bacteria and eukaryotic algae, oxygen and carbon dioxide molecules move by diffusion through cell membranes. Larger multi-cellular organisms such ...