High central plateaus sandwiched between tall mountains
Answer:
antigen-MHC protein complexes
Explanation:
Helper T-cells recognise antigens that are complexed with MHC proteins and interact with target cells. Antibodies can be produced against a single antigen in a variety of ways. Toxic shock syndrome is a relatively mild condition that resembles other minor allergy responses. Antigen-presenting cells break down superantigens.
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Answer:
The nitrogen cycle could not exist without the presence of nitrogen-fixing microorganisms.
Explanation:
As part of the biogeochemical cycles that occur in nature, the nitrogen cycle involves all the organic and non-organic processes that allow the incorporation of this element into the organism of living beings.
Although nitrogen is abundant in nature, in gaseous form, living beings cannot take advantage of it, because they lack the ability to convert this gas into organic nitrogen. Nitrogen-fixing microorganisms -such as bacteria in the soil- turn inorganic nitrogen into organic, that incorporates plants.
Nitrogen-fixing bacteria exist in both soil and plant roots. They are responsible for the conversion of atmospheric nitrogen and ammonium, the product of the degradation of organic matter, into nitrites and nitrates that assimilate the plants. Herbivorous animals obtain this nitrogen from vegetables, and carnivores from them.
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