Question

a researcher hypothesizes that water will move out of the cell more quickly when the concentration of salt in the water outside the cell is greater. which experiment would best test this hypothesis?
a a researcher places three cells of the same type in varying concentrations of salt water. then the researcher measures the size of each cell every minute during a 5 - minute period of time.

b a researcher places three cells of the same type in the same concentration of salt water. then the researcher measures the size of each cell every minute during a 5 - minute period of time.

c a researcher places cells from three different fish in varying concentrations of salt water. then the researcher measures the size of each cell at the end of a 5 - minute period of time.

d a researcher places cells from three different fish in the same concentration of salt water. then the researcher measures the size of each cell at the end of a 5 - minute period of time.

Explanation:

The hypothesis is about how water movement (related to salt concentration difference) affects cells. To test if water moves out faster when external salt concentration is higher, we need to vary the external salt concentration (independent variable) and measure the effect on cells (dependent variable, like cell size change over time or at the end). Option A uses the same cell type (controlling variables) and varying salt concentrations (to test the hypothesis), and measures cell size during the 5 - minute period (to see the rate of change, which is relevant to "more quickly"). Option B uses the same salt concentration, so it can't test the effect of different external concentrations. Option C uses different fish cells, introducing more variables. Option D measures only at the end, and using different fish cells also adds variability. So A is the best as it manipulates the independent variable (salt concentration) and measures the dependent variable (cell size over time) with controlled cell type.

Answer:

A. A researcher places three cells of the same type in varying concentrations of salt water. Then the researcher measures the size of each cell every minute during a 5 - minute period of time.