Teperature
Ph level
Substrate concentration
Not sure if these are physical but hope it helped.
The Parasite harms host
The parasite must adapt to beat host's defenses <span />
Answer:
nitrogen fixation is the answer
Stem cell therapies are not new. Doctors have been performing bone marrow stem cell transplants for decades. But when scientists learned how to remove stem cells from human embryos in 1998, both excitement and controversy ensued.
The excitement was due to the huge potential these cells have in curing human disease. The controversy centered on the moral implications of destroying human embryos. Political leaders began to debate over how to regulate and fund research involving human embryonic stem (hES) cells.
Newer breakthroughs may bring this debate to an end. In 2006 scientists learned how to stimulate a patient's own cells to behave like embryonic stem cells. These cells are reducing the need for human embryos in research and opening up exciting new possibilities for stem cell therapies.
The answer is D
Explanation:
I apologise for the late answer, but D would be the best one, as it does not discuss morality or anything differing from person to person. The effect it has on birds however, can be readily studied using the scientific method.
