Hey sophomore, hope this helps

Well what the number one thing one needs to know about diffusion is that diffusion is the spreading of something more widely. In other words diffusion is the movement from high to low concentration. To get into the roots of diffusion I am going to start out with passive diffusion. There are two passive diffusion; simple and facilitated diffusion and both do not need energy. Simple diffusion is when a small non-polar molecule passes through a lipid bi-layer. Also i does not involve a protein and one example is osmosis, osmosis is the movement of water. Facilitated on the other hand is diffusion through protein channels. A channels move specific molecules across cell membrane and yet again uses no energy. Lastly there is active transport to talk about.What active transport is the movement of molecules against concentration gradient in other words change transports solute from one side of the membrane to the other; a protein "pump". To do this is uses ATP (a form of energy).

My advice to you sophomore to help you remember is brake it down and remember the main points (found in yellow) also i hope my overall list helps....

Diffusion  = movement from high to low concentration

Passive Diffusion

• Simple and Facilitated Diffusion  
• No need energy

Simple Diffusion 

• small non-polar molecule passes through a lipid bi-layer 
• No protein
• Example Osmosis 

Osmosis

• Movement of water

Facilitated 

•  diffusion through protein channels 
•  specific molecules across cell membrane 

Active Transport 

• movement of molecules against concentration gradient 
• change transports solute from one side of the membrane to the other
•  a protein "pump"
•   uses ATP (energy).

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