The lower respiratory tract is essentially sterile because epithelium lining is the respiratory tract that covers the bottom respiratory tract sterile. It basically prevented the mucus accumulation in lungs. The macrophages is the immune system part that can digest or inhaled any harmful substances.
plants that are shorter and need little to no soil are most efficient. Lichens, which are part fungus and usually part algae, don't need extensive root or water-transportation system
