IMMUNOLOGY

Detailed explanation-1: -The most basic protective function of surface epithelial cells is to provide a structural barrier. This both hinders the entry of pathogens, noxious chemicals, and physical objects into interior tissues, and prevents the egress of interstitial fluids.

Detailed explanation-2: -The skin, mucous membranes, and endothelia throughout the body serve as physical barriers that prevent microbes from reaching potential sites of infection. Tight cell junctions in these tissues prevent microbes from passing through.

Detailed explanation-3: -Natural barriers include the skin, mucous membranes, tears, earwax, mucus, and stomach acid. Also, the normal flow of urine washes out microorganisms that enter the urinary tract.

Detailed explanation-4: -Cell wall is the physical barrier which can prevent protoplast fusion. Cell wall; which is made up of cellulose and pectin is dissolved with the help of enzyme cellulase and pectinase respectively. The fusion of protoplast is then carried out by electrical and or chemical processes.