To engage students in today's lesson, I activate students prior knowledge by asking them to develop explanations for three every day phenomena. Students are given the choice of either writing or drawing their explanation.
The phenomena are:
1) Making tea with a tea bag
2) Air freshener
3) Putting on perfume
Once students have written or drawn their explanations I ask students if they notice any similarities between all three events. What I'm looking for is for students to say that either the tea, air freshener, or perfume spreads across space (the room, the mug).
I follow this quick discussion by showing students two time lapse videos that show large crowds leaving an event.
The reason I show this video is to show students another example of diffusion (in this case humans moving from an area of high concentration to an area of low concentration).
Once the videos have finished playing, I ask the students to identify a common theme between the videos and the three everyday events they thought about earlier. The goal is to have students use these experiences, coupled with the videos, to come to a conclusion that "stuff" (matter) tends to move from an area of high concentration to an area of low concentration.
In this section of lesson we further explore this movement from areas of high concentration to areas of low concentration by completing an Egg Osmosis Lab. (SP2 - Develop and Using Models - Develop and use a model to describe phenomena and unobservable mechanisms.)
This lesson follows a lesson on cell membrane structure and function, where students explored the characteristics of cell membranes that allow it to be selectively permeable (Crosscutting Concept -Structure and function - The way in which an object or living thing is shaped and its substructure determine many of its properties and functions.)
In this lab students explore diffusion/osmosis which is one of the mechanisms that cells use to transport substances across the cell membrane (MS-LS1-2 -Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.)
It is important to note that the Egg Osmosis Lab requires a couple of days to see results in both Step 1 and Step 2. In addition depending on math proficiency of students you might need to take a day for data analysis specifically when calculating % weight change. (SP 3- Planning and Carrying out Investigations - Conduct and Investigation to produce data to serve as the basis for evidence that meets the goals of an investigation).
1. Raw eggs can carry salmonella (harmful bacteria). Be sure to wash your hands after handling the eggs.
2. Handle your egg very carefully so that it does not break
To soak an egg in various liquids and observe how the size of the egg changes as it gains or loses water through the membrane.
Raw eggs, 300 ml vinegar, tap water, salt water, and a liquid of your choice (corn syrup), metric tape, balance, plastic container to hold egg, beaker, marker, masking tape
Predict how eggs will respond when it is soaked in:
2. Distilled Water
3. Corn Syrup
4. Salt Water
Procedure Step 1: Soaking egg in vinegar
1. Label your container with your section and table number.
2. In the data table, make a drawing and observation of the eggs in the appropriate space
3. To Measure Your Eggs, use a flexible tape measure, measure the circumference of the egg (along the “equator”). Record circumference to closest millimeter.
4. Weigh the eggs in grams. Record mass
5. Pour 300 ml of vinegar into the container.
6. Carefully place eggs into the container and allow it to soak 2 days. Loosely place lid on top; if placed too tight it may break!
7. Put your container in the designated space.
8. Clean up materials and wash your hands.
Procedure Step 2: Soaking egg in distilled water, corn syrup, salt water
1. Carefully remove eggs from the container of vinegar.
2. Remove any remaining bits of shell by gently running eggs under water. Blot it dry with a paper towel.
3. Measure and mass your eggs and record observations in data table
4. Pour used vinegar down the drain. Rinse container
5. Place 3 eggs in separate liquids: distilled water, corn syrup, salt water
6. Allow each egg to soak 2 days
7. Put containers in designated space, clean up materials and wash your hands.
Data Analysis is found on page 3 and 4 of Egg Osmosis Lab.
In this section of lesson I explain the concepts of science diffusion and osmosis through the following websites.
Note this part of lesson occurs after students have completed lab and data analysis.
1) Diffusion - this website does a great job at explaining the concept through an animation.
2) Osmosis - this website does a great job at explaining the concept through an animation.
In order to explain the concepts of hypotonic and hypertonic solutions I shows students the following visuals. This explanation is necessary for students to understand the science behind the contrast in appearance of egg after being soaked in water and salt water/corn syrup.
I end this explanation portion of the lesson by showing students the video below, which summarizes the week-long lab in 5 minutes.
To assess student understanding I have students complete Diffusion Osmosis Review after video.
In this section of lesson I have students read an article on diffusion/osmosis from cK-12.
The objective of this reading is to reinforce what we have learned so far in class.
Once students have read article, students answer the following questions:
Once students have completed the exercise below I have students visit Dirty Blood.
This website introduces students to dialysis, a real world application of diffusion. The objective of this video is to demonstrate to students that what we learn in science class has relevance to our everyday lives, in this case the survival of a human being.
If time permits you may show students the picture below that demonstrates how peritoneal dialysis works through diffusion in the human body. Awesome !!!!
In this section of the lesson students complete an Exit Ticket. In this exit ticket students write an explanatory/informative text on the relationship between the structure and function of a cell membrane (SP7 - Engaging in Argument form Evidence - Use an oral or written argument supported by evidence to support or refute an explanation or a model for a phenomenon & W.7.2 -Write informative/explanatory texts to examine a topic and convey ideas, concepts, and information through the selection, organization, and analysis of relevant content.)
Students use the Claim, Evidence, Reasoning, and Conclusion model to write their argument. Students are graded using a 4 point Rubric which scores them on all 4 areas of CERC in addition to organization.
I have attached a link to my CERC - Writing an Evidence Based Argument lesson which shows how I model this important writing process for my students.