20
1. what does the term carrying capacity describe?
a) the maximum number of birth rates for a population.
b) the ability of a population to accept new immigrants.
c) the population size that the environment can sustain.
d) the ratio of birth rates to death rates in a population.
2. which factor is a density-dependent limiting factor on the population of a species?
a) predation
b) unusual weather
c) natural disasters
d) seasonal variation
3. which nutrient cycle is most affected by the over-use of ammonia fertilizers on commercial farms, as well as by the accumulation of waste on cattle farms and feed lots?
a) water
b) carbon
c) nitrogen
d) phosphorus

A3.37-mg sample of protein was chemically digested to convert its nitrogen into ammonia and then diluted to 100.0 ml. then 10.0 ml of this solution was placed in a 50-ml volumetric flask and treated with 5 ml of phenol solution plus 2 ml of sodium hypochlorite solution. the sample was diluted to 50.0 ml, and the absorbance at 625 nm was measured in a 1.00-cm cuvette and found to be 0.486. for reference, a standard solution was prepared from 10.0 mg of nh4cl (molar mass = 53.49 grams/mole) dissolved in 1.00 l of water. then 10.0 ml of this standard was placed in a 50-ml volumetric flask, treated in the same manner as the unknown, and the absorbance found to be 0.323. finally, a reagent blank was prepared using distilled water in place of unknown, it was treated in the same manner as the unknown, and the absorbance found to be 0.076. calculate the weight percent of nitrogen in the protein.