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Table 2 Scoring rubric of the constructive-response item on differential height

From: Comparing the effects of dynamic computer visualization on undergraduate students’ understanding of osmosis with randomized posttest-only control group design

Score

Level

Description

Students’ responses

0

No answer

Off-task

[blank]

Students write some text that either makes no meaning or no attempt to respond to the question stem.

I don’t know what will happen (Off-task)

I have no clue (Off-task)

1

Simple statement

No apparent indication of ideas listed above or isolated concepts and/or misconception

Only repeat the information in the question stem.

Irrelevant to the ideas listed above.

Only relevant, but isolated concepts

Only misconceptions

Diffusion.(Only relevant, but isolated concepts)

Some water will diffuse for equilibrium (Only relevant, but isolated concepts)

Dilute sugar water wont cause any movement (Irrelevant to the ideas listed above)

2

Partial

Have one relevant and correct idea

Provide one stand-alone relevant idea that is listed above.

[may contain incorrect responses]

The concentration of sugar (solute) is higher on the left side, therefore water will move down its concentration gradient to the left side of the permeable membrane causing the height to change (Idea No.2)

We need to know how much volume of each was poured into each side.(Idea No.4)

3

Complete

Include two scientifically valid ideas relevant to the given context

Meaningfully provide two ideas listed above

[may contain incorrect responses]

The height depends on the the ideal equilibrium based on the solute concentrations versus the force of gravity on each side (Idea No.1). We know the force of gravity, but not the exact concentration of solute or rate of diffusion from one side to the other. Therefore, we do not know where the balance lies between the two force (Idea No.4)

4

Exceptional

Elaborate three or more scientifically valid ideas relevant to the given context

Meaningfully provide three or all of the four ideas listed above [may contain incorrect responses]

I think that it would depend on how large the difference is in concentration. It comes back to whether or not the osmotic force is large enough to overcome gravity (Idea No.1). Osmosis would predict that the water level would stay much higher on the left (Idea No.2) while gravity would predict that the two levels would even out (Idea NO.3). If the difference in solute concentration was high enough, then I believe that osmosis could potentially overcome gravity.

  1. Key ideas:
  2. 1. The movement of free water is determined by two factors here, the concentration difference and the hydrostatic pressure difference
  3. 2. Some water diffuses from the right side to the left side because the left side has higher solute concentration than the right side
  4. 3. Some (free) water diffuses from the left side to the right side because the left side has a higher hydrostatic pressure than the right side initially
  5. 4. We cannot predict what happens to the height of each column because we do not know the initial relation between the hydrostatic pressure difference and the solute concentration difference (or because we do not know the exact height difference and the solute concentration initially)