Three lab groups carried out an experiment to identify the correct molarities for five solutions. Each unknown contained one of the following sucrose concentrations: 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M. Each data entry represents the average of 3 sample replications of 1 cm3 sweet potato cubes expressed as percent change in mass after an overnight (24 hr) soak in the unknown solutions. From the data given, which statement most accurately describes what is occurring in response to a particular unknown solution.

B) Osmosis of water molecules from unknown solution A likely caused the increase in mass observed.

Explanation:

Osmosis is a type of diffusion (a random movement of molecules to an area of lower concentration from an area of higher concentration) of water. Like other molecules, water can pass through a cell membrane and it will diffuse across the membrane, along its own concentration gradient independent of other particles that could be present in solution. The concentration of water in a solution is inversely (opposite) related to the concentration of the solute, meaning that water will move from a region of high water potential to a region of lower water potential during osmosis.

Unknown solution A had the highest water potential with a sucrose concentration of 0.0 M. This means that water diffused through the membranes of the cells in the sweet potato cube as it moved along its own concentration gradient (from a region of high water potential to a region of lower water potential) causing an increase in the mass of the sweet potato cube

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.