The answer for this question would be Integument, digestive, respiratory and urogenital.
The largest system that contact with the external environment would be integument and digestive. That makes two system has normal flora of microbes and not sterile like the other systems. Normal flora of microbes will prevent the pathogen microbe grows so it gives some benefit.
It has two phosppholipid layers that are either hydrophobic and hydrophillic the function is to protect thing from coming in and out
Answer:
Hormones
Explanation:
Hormones travel through the body
Sand and glass have different chemical formulas, so that means that the atoms are rearranged and this is a chemical reaction.
