Answer:
b. They express the appropriate receptor.
Explanation:
The signal transductions are extraordinarily specific and sensitive. Specificity is achieved by a <u>precise molecular complementarity between the signal molecules and the recepto</u>r. For example, the thyrotropin-releasing hormone produces a response in cells of the adenohypophysis, but not in hepatocytes, which lack the receptors to this hormone.
Answer:
In order to be useful in treating human infections, antibiotics must selectively target bacteria for eradication and not the cells of its human host. Indeed, modern antibiotics act either on processes that are unique to bacteria--such as the synthesis of cell walls or folic acid--or on bacterium-specific targets within processes that are common to both bacterium and human cells, including protein or DNA replication. Following are some examples.
Most bacteria produce a cell wall that is composed partly of a macromolecule called peptidoglycan, itself made up of amino sugars and short peptides. Human cells do not make or need peptidoglycan. Penicillin, one of the first antibiotics to be used widely, prevents the final cross-linking step, or transpeptidation, in assembly of this macromolecule. The result is a very fragile cell wall that bursts, killing the bacterium. No harm comes to the human host because penicillin does not inhibit any biochemical process that goes on within us.
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Explanation:
Answer:
The correct answer is A. a rotating cloud of dust and gas.
Explanation:
Nebulae are regions of the interstellar medium (clouds) made up of gases (mainly hydrogen and helium) and dust. In other words, nebulae are concentrations of gas in which we find hydrogen, helium and stardust in greater quantities. They are structures that are actually very important for the universe, this because inside it is the place where stars are born, which arise due to the condensation and aggregation of matter. The nebular theory states that the Solar System reached the form current from a solar nebula (a gas cloud), more than 4.5 billion years ago. The large cloud of molecular gas was affected by a certain phenomenon that would have taken place in the vicinity. Like the explosion of a supernova or the passage of a star that would produce a strong gravitational impact. The result of this event made the matter agglomerate in different places. The high concentration of matter caused the nebula to collapse. Becoming a protostar, (bodies whose characteristic is to be surrounded by clouds and contain preplanetary matter inside), that is, gaseous matter in the outermost part and solid inward. At the core of this structure, the temperature is so dominant that nuclear reactions take place to compensate for the gravitational force. This leads to a hydrostatic equilibrium and the formation of a fundamental star: the Sun. The rest of the mass flattened, forming a protoplanetary disk where the protoplanets were being formed, which would evolve to become the current planets, their satellites and the others bodies of the solar system.
Energy flow is the amount of energy that moves through a food chain
chemical cycling is the flow of elements and compounds between living organisms and the physical environment
