Bacteria, pollen, and transplanted tissue are examples of Foreign antigens.
The source of foreign antigens is external to the body. Examples include components of or compounds created by viruses, microorganisms (such as bacteria and protozoa), substances in snake venom, specific proteins in meals, pollens and serum and red blood cell components from other people.
T cells only identify foreign antigens that are present on the surfaces of the body's own cells, as opposed to immunoglobulins, which interact with infections and their harmful products in the extracellular spaces of the body.
These antigens may come from pathogens that proliferate inside of cells, such as viruses or intracellular bacteria, or they may come from pathogens or their byproducts that cells have ingested through the process of endocytosis.
Animals get thenitrogen they need by eating plants or other animals that contain nitrogen. When organisms die, their bodies decompose bringing the nitrogen into soil on land or into ocean water.
Through the process of cellular respiration, the energy in food is converted into energy that can be used by the body's cells. During cellular respiration, glucose and oxygen are converted into carbon dioxide and water, and the energy is transferred to ATP
