In this interactive demonstration, students make observations of the process of diffusion. Students draw and record observations, make predictions and make comparisons between what they're observing and how a cell membrane works. All observations, questions, predictions and comparisons are recorded in their science notebooks. A teacher's worksheet is provided with suggested guiding questions and other set-up information.
This activity is designed for students to:
1. carefully make and record observations
2. think critically about what they are observing
3. make comparisons between their observations and the function of cell membranes
1. cell membranes regulate what can enter and exit the cell
2. diffusion is one process cells use to move materials between their internal and external environments.
Context for Use
This interactive demonstration is conducted in a 7th grade science classroom with 25-30 students. This activity generally takes one, 52 min. class period with possible discussion leading into the next day. The equipment needed consists of 2 beakers, sandwich baggies, iodine, starch and distilled water. This activity is usually done after we've discussed the parts of a cell and their functions. This activity would be very easy to adapt to other settings because the required material is easy to transport.
Subject: Biology:Cell Biology:Cell Processes:Membrane Transport
Resource Type: Activities:Lab Activity, Classroom Activity:Short Activity:Demonstration
Grade Level: Middle (6-8)
Description and Teaching Materials
See attachments Instructor's Notes (Microsoft Word 31kB Sep25 07) Dichotomous rubric (Microsoft Word 214kB Sep25 07)
Teaching Notes and Tips
I have also tried this demonstration as a lab where each lab group has all of the material in front of them. I found that most students ended up getting lost in the instructions and failed to record all of the observations I wanted. By doing a demonstration where the teacher is able to pace/guide the lesson and make sure everybody is following along, it seemed that the students had a better understanding of the concepts and were less confused throughout the demonstration.
As the demonstration is going on I am able to walk around and make observations and answer student questions. The final product will be their observations and other data students recorded in their science notebooks. I specifically check the final question to see if students are able to make comparisons between what they observed and the functions of a cell membrane. Student work is assessed using a dichotomous rubric that is created by the teacher and students in class.
7.I.B.4 - The student will explain how classroom scientific investigations relate to established scientific principles.
The student will understand that all organisms are composed of cells that carry on the many functions needed to sustain life. (1.IV.A.1 - cells are the fundamental units of life.)
References and Resources