Answer: Option B
Explanation: The first line of defense acts a barrier and does not allows the foreign materials to enter inside the body. It includes chemical and physical barriers that are always ready to protect the body from infection.
Example: Skin and mucous membrane.
Skin is largest organ and it acts as a barrier between pathogens and human body. It acts a waterproof material and the pathogens cannot get inside through skin unless the skin is broken.
Mucous membranes also acts as first line of defense and breaks the cell wall of many bacteria entering through the openings of the body.
So, skin and mucous membrane are the first line of defense.
EDTA inhibits the activity of DNase during DNA isolation process.
DNase is an enzyme which degrades DNA using divalent metal ions like Mg^{2+} . These metal ions act as cofactor for the proper functioning of DNase.
EDTA chelates the divalent metal ions and thus does not allow DNase to access them.
Therefore in this way DNA is prevented from degradation during its isolation.
