The LD 50 is a number scientists use in research to determine the dose of a toxin required to kill 50% of a population of organisms. Biologists in Louisiana have become concerned about cadmium levels in the water near New Orleans, and the chance that frogs will die out.

Scientists have performed an experiment on bullfrog tadpoles In Louisiana and the results are presented in the graph. The LD 50 for bullfrogs is reached

A) at about 6 mg per gallon per day.
B) at about 60% of surviving tadpoles.
C) somewhere around 11 mg per gallon per day.
D) somewhere between 2 mg and 3 mg per gallon per d

economic impact of malaria is estimated to cost africa $12 billion every year. this figure factors in costs of health care, absenteeism, days lost in education, decreased productivity due to brain damage from cerebral malaria, and loss of investment and tourism.

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.