Which of the following statement is true?
a. the nitrogen cycle is the most important cycle for life.
b. the oxygen cycle is the least important cycle for life.
c. life can be sustained without any of the cycles for life present.
d. all the cycles of the matter are equally important for life to be sustained

How many variables are altered in a good experiment? a.1 b.0 c.2 d.3

Contrast how pollination is different among gymnosperms and angiosperms.

Juan and carol were studying invertebrates in biology. they knew that segmented or earth worms preferred a dark, moist habitat. during this lab, they would be investigating the responses of organisms called planaria or dugesia tigrina. these were simple flatworms that still had a one-way digestive system and a very simple nervous system. juan and carol placed the planaria in a petri dish containing cool, distilled water that was partially covered with black paper. they shined a light on the dish. next, they removed the paper and placed a small amount of chicken liver at one end of the dish. they added a few large salt crystals to the water. finally, they added drops of hot water to the cool water in the petri dish. their results can be seen in the data table. according to their experiment, all but one conclusion is valid.