Which is a basic unit of a sugar molecule? a)amino acid b)fatty acid c)monosaccharide d)nucleotide which nitrogen base replaces thymine (t) in rna? a)uracil (u) b)cytosine(c) c)adenine (a) d)guanine (g) which is a carbohydrate? a)nucleic acid b)polysaccharide c)amino acid d)nucleotide what kinds of lipids make up the bilayer that forms cell membranes? a)phospholipids b)saturated fats c)steroids d)unsaturated fats how does an enzyme’s active site relate to its substrate? a)one is soluble in water, and the other is insoluble. b)they are identical in chemical makeup. c)their shapes fit snugly together. d)they are both used up by a single chemical reaction.

Experiments in environmental toxicology can sometimes be manipulative experiments in which the researcher actively chooses and manipulates the independent variable. in hunt's study, for example, dosages of bpa were manipulated and the effects were measured. in manipulative studies, the researcher controls all the other variables in the experiment, so any health effects observed in the test subjects can be attributed to differences in the independent variable. in other cases, researchers use natural experiments in which the dependent variable (typically a measure of organism health) is measured under differing contexts that are not manipulated. say, for example, that an accidental chemical spill contaminates five ponds. to determine the possible effects of the toxic chemical on frogs, a researcher could compare the hatching rate of frog eggs laid in those five ponds to the hatching rate of eggs laid in five uncontaminated ponds nearby. this would be an example of a natural experiment because concentrations of the toxic chemical in the ponds were not controlled by the experimenter, but rather resulted from the chemical spill. drag type of experiment on the left to the example of experiment on the right. blood concentrations of bpa in college students are compared to their recent manipulative consumption of canned food items 2. the feeding behavior of fish in streams that receive acidic runoff from strip mines is compared to the feeding behavior of fish in unaffected streams. the deformity rate in baby birds from nests in pesticide-sprayed fields is compared to the deformity rate in birds from nests in unsprayed fields 4 tumor development is compared in mice exposed to five dosages of a known carcinogen in the laboratory foraging activity levels are compared in tadpoles exposed to four concentrations of toxic metals in the laboratory. growth of corn plants is compared in field plots sprayed with three different dosage: s of weed killer 7 bpa concentrations in the urine of people with diabetes are compared to bpa concentrations in the urine of people without diabetes - natural; manipulative

What property of water provides for appropriate sugar, salt, and amino acid levels to be present and carried in the blood of animals to be delivered to cells

How has biodiversity on earth changed over time?