A portal of entry<span> is the site through which micro-organisms enter the susceptible host and cause disease/infection. Infectious agents enter the body through various </span>portals<span>, including the mucous membranes, the skin, the respiratory and the gastrointestinal tracts.</span>
They are composed of actin, troponin, tropomyosin, and myosin
The simple microscopic organisms the only life forms on earth was 560 million years.
