The cell membrane is a highly selective barrier that controls the movement of substances in and out of the cell. in fact, polar molecules are unable to go across unless a. they are broken down into smaller pieces. b. they are enclosed in water-filled vesicles. c. they pass through channels in the cell membrane. d. they react with other substances to become nonpolar.

Approximately what portion of the foods that we eat have been genetically modified in some way? a.fewer than 10% b.about 50% c.nearly 100%

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.

How energy flows through each level in this energy pyramid. is all the matter and energy from one level transferred to the next level?