<span>Variation among individuals in a species is real and important.</span>
The answer is C. solid iron and nickel
DNA We can change how cells interact
The nervous system communicates through electrical impulses and the communication is very fast. It works in a relay fashion, from point to point comparable to the way the old telephones systems used to work.
The endocrine system communicates by chemical signals via the bloodstream. Hormones are secreted into the blood and extra cellular fluids, then transported to target cells, which must bear a receptor to be able to bind to a specific hormone, and respond.
Hormones are chemical messengers secreted into blood or extracellular fluid that affect the function of other cells.
Endocrine communication is not quite as fast as the nervous system communication
Answer: we can make observations directly by seeing, feeling, hearing, and smelling, but we can also extend and refine our basic senses with tools: thermometers, microscopes, telescopes, radar, radiation sensors, X-ray crystallography, mass spectroscopy, etc. And these tools do a better job of observing than we can!
