option 2 seems appropriate for me!
The answer for the first question is B. mucus sweat and tears, all of those are defenses that the body uses when attacked. Now for the second option is A the answer because the first filter that a virus or a desease must pass is indeed the skin. Hope is good for you
Answer:
The ligand has only one receptor that it is able to bind to
Explanation:
The shape of the ligand and its corresponding receptor allow there to be specificity. For example, receptors for ligand A would be found on the target immune system cells and not on cardiac muscle cells or skin epithelial cells. Therfore, even though the cardiac muscle cells or the skin epithelial cells would be exposed to ligand A, they would not be able to bind to it and therefore could not react because of the specificity of the receptor of ligand A at that moment
Answer: Cells typically receive signals in chemical form via various signaling molecules.
I believe it is seminal fluid.
Hope this helps :)
