Experiments or observational studies in which only one variable is manipulated are described as

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.

High blood pressure occurs when there is too much blood flowing through the blood vessels at one time. by changing the amount of water in the blood, blood pressure can change. the excretory system can to lower blood pressure. which would most likely occur in the kidney? a)more water would be transferred from the nephron. b)less water would be absorbed into the nephron. c)the amount of water in the bladder would decrease. d)the amount of water in the blood would increase.

10 15 20 time (minutes) using the graph of data from this experiment, at which point was the light source most likely removed? ob