The atmosphere is a closed system.
False
Endotherms, such as birds and mammals, use metabolic heat to maintain a stable internal temperature, often one different from the environment. Ectotherms, like lizards and snakes, do not use metabolic heat to maintain their body temperature but take on the temperature of the environment.
The responses observed in type IV hypersensitivities result from the action of T cells and phagocytes.
Hypersensitivity IV type, also called delayed-type hypersensitivity (DTH), involves T cell-antigen interactions that cause activation and secretion of cytokines. This type of hypersensitivity requires sensitized lymphocytes that respond 24–48 hours after exposure to soluble antigens. A type IV hypersensitivity reaction is a cell-mediated reaction that can occur in response to contact with certain allergens, resulting in what is called contact dermatitis, or in response to certain diagnostic procedures such as the tuberculin skin test. Certain allergens need to be avoided to treat this condition. Type IV hypersensitivity response is observed results from the action of T cells and macrophages while other types are mediated by antibodies. This reaction occurs at least 1–3 days after the initial exposure. Type IV hypersensitivity is the mechanism of many autoimmune disorders.
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Scientific theory definition, a coherent group of propositions formulated to explain a group of facts or phenomena in the natural world and repeatedly confirmed through experiment or observation: the scientific theory of evolution.
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