Sarah performs an experiment to determine the effect of nitrogen on plants. she studies the effect of nitrogen on the growth of the root of hair, height of the plants, and nodule formation. which factor is an independent variable ?

Nitrogen

Explanation:

An independent variable can be changed, altered or manipulated by the experimenter so as to observe the result of such manipulation on the test variable or experimental variable or dependent variable.

Here, nitrogen is the independent variable. The effect of which can be observed on growth of the roots of hair, height of the plants and nodule formation all these factors are the examples of the dependent variables.        

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.