Answer:
- Physical and chemical barriers
- non-specific innate responses
- specific adaptive responses
The differences are...
The first barrier is the physical and chemical barrier. It is the first line of defense when in contact with outside sources, this can be through the skin, earwax, nose-hair, etc.
The second barrier, the non-specific innate response, is after these outside sources have somehow managed to pass through the first barrier. They come into contact with cells and enzymes that help to defeat them.
The third barrier, the specific adaptive response, is the body's way of dealing with pathogens that the body has encountered before. (B cells activate)