ADI: biology and osmosis

This activity is based on Question 17 of the Biology I Form 1 EOC, which uses potato mass to relate to diffusion through solution concentrations relative to the potato.

In developing the correct answer to this question, students must demonstrate knowledge of the topic (diffusion), the process (two interacting systems with varying solution differences) and the molecular interactions behind the outcomes. This type of system is basic enough to understand while still preserving a level of fundamental complexity that lends itself toward the ADI model in any classroom.

Step 1: Identification

• Give the setup for the problem. Include the materials (potatoes, different concentrations of glucose solutions, a timer, etc) and the concepts behind the problem (what diffusion is, vocabulary like hypo/hyper/isotonic, what water uptake in the potato looks like (increased mass), and relevant examples in daily life pertaining to diffusion -- like not drinking saltwater when you're dehydrated, or the smell of perfume in the air, and so on.

Step 2: Generation of data

• Students use their knowledge of potato mass in determining water uptake to quantify the concentration gradient for a particular solution. This involves massing the potatoes before and after immersion in the given concentrations. Strong investigation should pay attention to significant figures and proper massing.

Step 3: Production of a Tentative Argument

• Students analyze their quantified data by ascribing a relationship between variables -- that is, solution concentration and potato mass. They delve deeper into the interaction and recognise that the potato mass is merely a vehicle for the water uptake, then further demonstrate understanding by explaining the relationship between water uptake and rate of diffusion, using vocabulary terms. Models such as diagrams, charts, and pictures can be used in the visual presentation to help facilitate understanding and support their argument.

Step 4: Interactive Argumentation Session

• The class splits into the "round robin" model of group discussions, focusing on individual groups' interpretations of data and what discrepancies and similarities exist in method and analysis between different groups. Students come back to their own groups and devise a better method or more involved analysis toward understanding the problem.

Step 5: Creation of a Written Investigative Report

• Transcribe the findings and methods of the experiment into a readable report, also highlighting problem areas (proper tool use), room for error (inexact measurements), suggestions for a better experiment next time (control for temperature of solution), and practical applications for the understanding of the problem, just to give a few examples.

Step 6-7: Double-blind peer review, revision

• Spend time qualitatively analyzing other groups' reports through the checklist. Identify areas that need to be clarified or better organized, and read to be sure their argument on the relationship between potato mass and solution concentration stands on their evidence alone. Revise toward those standards and continue to strive toward a strong, clear argument.

Step 8: Reflective discussion

• This is where the entire class will come together and contribute personal findings and thoughts on not just the problem, but the way the class conducted discussions together throughout the interactive processes of argument and report review. Moreover, the teacher can facilitate discussion about the practical relevance of diffusion, further cementing the utility in experimental modeling and why understanding a topic matters. The students should finish the ADI process with a better comprehension of the scientific material and the model used to promote inquiry, discussion, and review.