Hemoglobin protein is produced by red blood cells, but liver cells from the same organism do not produce hemoglobin protein. Why?

A. The gene for hemoglobin is missing in liver cells
B. the gene for hemoglobin is turned off in liver cells
C. The gene for hemoglobin has mutated in liver cells
D. The gene for hemoglobin is activated in liver cells

Epinephrine is a hormone released from the adrenal gland of the body, most often in a stressful situation. it is known as the "fight-or-flight" hormone. one way that it causes a response in the body is to activate receptors on muscle cells. where are these cellular receptors located? a. on the cell membrane b. in the nucleus c. on the cell wall d. around the mitochondria

When does the circulatory system work with the respiratory system? a. during blood cell formation b. during cellular respiration c. during intestinal digestion d. during a viral infection

Match the pollutants. 1. a chlorofluorocarbon smoke 2. a biodegradable organophosphate insecticide freon 3. particle pollution paint 4. hazardous waste monoxide 5. carbon is completely burned malathion 6. carbon is incompletely burned dioxide