(DDT) is a chemical that was used widely to control pests in agricultural crops. DDT was banned in many countries in the 1970's when many predatory birds were experiencing thinning of their egg shells. The thinning led to low birth rates and low infant survival, which threatened some populations. The birds' habitat was too far from the crops for the birds to have been exposed directly to the DDT. The most likely explanation for DDT exposure in these birds, despite their distance from the source is

Select one:
a. the birds sometimes used the treated grain in building their nests, with the DDT leaching into the egg shells
b. that DDT remained in the tissue of plants, which were eaten by primary consumers and then the birds (at each tropic level, the concentration of DDT increased and caused the most harm to predatory birds)
c. the DDT remained in the air and was carried to the bird nests by wind and rain
d. that some other toxic chemical was harming the egg shells

Astudent from one of the research labs is having trouble preparing a slide for examination and photographing. the bacterial slide that he has brought to you was prepared using a commercially purchased stain. he has asked for your in determining what he is doing wrong so that he can change the lab protocols and continue on with his project. after examining the slide under oil immersion, you determine that no bacteria are present even though the student is able to show you the culture he used to make that slide that has visible growth in the liquid medium. which of the following statements does not explain the fact that there are no bacteria present on the student’s slide? by not allowing a glass slide to completely air dry before heat fixation, the flame will cause the surrounding water to boil and this will damage the bacterial cell. overheating during the fixation step boiled the water within the bacterial cells and resulted in the cells bursting. insufficient heating of the slide did not drive out the thin layer of water and this resulted in minimal bonding between the bacteria and the glass slide. rinsing with alcohol during the washing step stripped the bacteria off the glass slide. rinsing with alcohol during the washing step stripped the bacteria off the glass slide.