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

The tasmanian devil, a marsupial carnivore, is facing extinction due to devil facial tumor disease (dftd) which causes bulging cancerous lumps and lesions to erupt around the face and neck — often causing enough deformation to make seeing or eating difficult. dftd has evolved into a contagious cancer, a trait that is unique among cancers. devil mating behavior involves biting around the head and neck, allowing cells from one individual — especially cells from the crumbly dftd tumors — to be transferred to the wounds or face of a new individual. this marsupial was once found across australia, but sea levels rose, isolating the tasmanian population, while the australian population went extinct. what would be an outcome of genetic isolation that is likely to have impacted the spread of dftd? a) reduced territory puts diseased individuals in greater contact with non-diseased ones. b) inbreeding results in less variation in facial features so the cancer is generally fatal. c) genetic isolation has made it difficult for scientists to develop a vaccine against dftd. d) the lack of genetic variation in the immune system of tasmanian devils minimizes resistance to the disease.

Which of the following is not a symptom of desertification? a) decrease in salt content of the soil b) lowering of the water table c) reduced surface water d) increased soil erosion e) loss of native vegetation

Consider the skeleton. which skeletal system is represented by the shaded portion of the skeleton? spongy skeleton compact skeleton axial skeleton appendicular skeleton