*Question*
Answer the following question given this paragraph: Today in many countries, death rates have gone down but birth rates remain high. This means that the population is growing. Figure below shows the growth rates of human populations all over the world. Q: Which veins return oxygen-rich blood from the lungs to the heart? Choices: - jugular - varicose - respiratory - pulmonary A:
**Answer**
pulmonary

*Question*
Answer the following question given this paragraph: Complexing agents that tie up metal ions are also used as drugs. British Anti-Lewisite (BAL), HSCH2CH(SH)CH2OH, is a drug developed during World War I as an antidote for the arsenic-based war gas Lewisite. BAL is now used to treat poisoning by heavy metals, such as arsenic, mercury, thallium, and chromium. The drug is a ligand and functions by making a water-soluble chelate of the metal; the kidneys eliminate this metal chelate (Figure 19.31). Another polydentate ligand, enterobactin, which is isolated from certain bacteria, is used to form complexes of iron and thereby to control the severe iron buildup found in patients suffering from blood diseases such as Cooley's anemia, who require frequent transfusions. As the transfused blood breaks down, the usual metabolic processes that remove iron are overloaded, and excess iron can build up to fatal levels. Enterobactin forms a watersoluble complex with excess iron, and the body can safely eliminate this complex. Q: How does consuming enterobactin help our body? Choices: - builds excess iron - eliminates excess fat - eliminates excess oxygen - eliminates excess iron A:
**Answer**
eliminates excess iron

*Question*
Answer the following question given this paragraph: produced in cells located in the stomach wall. When food enters the stomach after a period of fasting, pepsinogen is converted to its active formpepsinin a series of steps initiated by the drop in pH. Pepsin catalyzes the hydrolysis of peptide linkages within protein molecules. It has a fairly broad specificity but acts preferentially on linkages involving the aromatic amino acids tryptophan, tyrosine, and phenylalanine, as well as methionine and leucine. Protein digestion is completed in the small intestine. Pancreatic juice, carried from the pancreas via the pancreatic duct, contains inactive enzymes such as trypsinogen and chymotrypsinogen. They are activated in the small intestine as follows (Figure 20.7 "Activation of Some Pancreatic Enzymes in the Small Intestine"): The intestinal mucosal cells secrete the proteolytic enzyme enteropeptidase, which converts trypsinogen to trypsin; trypsin then activates chymotrypsinogen to chymotrypsin (and also completes the activation of trypsinogen). Both of these active enzymes catalyze the hydrolysis of peptide bonds in protein chains. Chymotrypsin preferentially attacks peptide bonds involving the carboxyl groups of the aromatic amino acids (phenylalanine, tryptophan, and tyrosine). Trypsin attacks peptide bonds involving the carboxyl groups of the basic amino acids (lysine and arginine). Pancreatic juice also contains procarboxypeptidase, which is cleaved by trypsin to carboxypeptidase. The latter is an enzyme that catalyzes the hydrolysis of peptide linkages at the free carboxyl end of the peptide chain, resulting in the stepwise liberation of free amino acids from the carboxyl end of the polypeptide. Figure 20.7 Activation of Some Pancreatic Enzymes in the Small Intestine. Q: When food enters the stomach after a period of fasting, a drop in what initiates the conversion of pepsinogen to pepsin? Choices: - calcium - white blood cells - acid - ph A:
**Answer**
ph

*Question*
Answer the following question given this paragraph: Streams often start in mountains, where the land is very steep. You can see an example in Figure below . A mountain stream flows very quickly because of the steep slope. This causes a lot of erosion and very little deposition. The rapidly falling water digs down into the stream bed and makes it deeper. It carves a narrow, V-shaped channel. Q: Where do streams often start? Choices: - valleys - oceans - plains - mountains A:
**Answer**
mountains