Which statement best describes an individual ecosystem?
a. an closed system with regard to energy, but an open system with respect to matter.
b. an open system with regard to energy, but an open system with respect to matter.
c. a closed system with regard to both energy and matter
d. a open system with regard to both energy and matter.

Why is the theory of evolution important? it disproves all other theories about how life began. it provides a topic for debate. it is a unifying concept in biology. it explains how life began. i know for sure, it is not "it is a unifying concept in biology."

Hormones are chemical molecules produced by endocrine glands. one such endocrine gland is the thyroid gland, which synthesizes the thyroid hormone, which in turn affects the heart muscles. which two statements describe the probable reason for the function of the hormone? the cells in the heart have specific receptors that allow for the intake of hormones. the heart and the endocrine glands have the exact same types of cells. all cells make the same types of hormones. thyroid hormones show their effect on the heart by means of specialized cells. thyroid cells and cardiac cells have different dna.

_tissues respond quickly to outside stimuli a) epithelia b)nervous c)muscular d)muscular and nervous