In this lesson, students learn about the molecules that are produced in cells and their uses for cells. Students test for carbohydrates, proteins, and lipids in various plant and animal organs and then analyze their data in order to determine the relationship between the organs and the molecules that are most prevalent in them.
This lesson specifically connects to the following NGSS and Common Core Standards:
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.
MS-LS1-7 Develop a model to describe how food is rearranged through chemical reactions forming new molecules that support growth and/or release energy as this matter moves through an organism.
CCSS.ELA-LITERACY.WHST.6-8.10 Write routinely over extended time frames (time for reflection and revision) and shorter time frames (a single sitting or a day or two) for a range of discipline-specific tasks, purposes, and audiences.
CCSS.ELA-LITERACY.RST.6-8.3 Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.
Science and Engineering Practices:
Designing and Carrying Out Investigations: Collect data to produce data to serve as the basis for evidence to answer scientific questions.
Analyze and Interpret Data: Analyze and interpret data to provide evidence for phenomena.
Patterns: Observed patterns in nature guide organization and classification and prompt questions about relationships and causes underlying them.
Systems and System Models: A system is an organized group of related objects or components; models can be used for understanding and predicting the behavior of systems.
Begin class by asking, "What are you going to learn today?" Students should respond by referring to the Essential Question, "How do cells contribute to the function of living organisms?". This EQ can be referenced both on my front board as well as on their Cells Unit Plan.
Have students get out their Cells Unit Plan. Explain that their focus of this particular lesson is Skill 3 (I can create a model that shows the relationship between cell structure and function) and Skill 4 (I can identify important materials and processes that are required for cells to function). Have students read the skill and self-assess where they stand in their level of mastery in this skill. Students rank themselves on a scale of 1 to 4 (4 being mastery).
As the unit moves forward, I have the students continually self-assess on each skill. In my class, this will be the students second self-assessment, so they change their scores if they feel that their learning has improved. Check out the student's unit plan below to see how students update their mastery level with each lesson.
I say, "Throughout science, there are concepts that can be applied to every situation. We have called these "crosscutting concepts". One of the crosscutting concepts that we have discussed is "Energy and Matter"."
On the projector, I put up the NGSS unwrapped version of the "Energy and Matter" crosscutting concept:
Energy and Matter: Flows, Cycles, and Conservation: Tracking energy and matter flows, into, out of, and within systems helps one understand their system’s behavior.
As a class, we break down what the meaning of this concept is and form an idea of what we would be looking for if we were trying to connect to it during a lab or reading. I explain that as we have gone through units on matter, chemistry, and energy, it is important to apply these concepts across units and find connections in our cells units.
Next, I read Cell Chemistry aloud to the class. After every sentence I pause and provide students with time to highlight/circle any word or concept that helps them connect to a the crosscutting concept "Energy and Matter". (Just so you are aware, I wrote this text and it is definitely written in "my voice". In addition, it is written from the perspective that the students have covered the chemistry and matter units.)
Reading aloud during this mini lesson is something that I made a deliberate decision to do. As Anne Guignon states as she writes for Education World, "Reading aloud to children helps them develop and improve literacy skills -- reading, writing, speaking, and listening.....And since children listen on a higher level than they read, listening to other readers stimulates growth and understanding of vocabulary and language patterns." As middle school teachers it is important to realize that reading aloud is not only for elementary teachers. All students benefit from hearing adults fluently read scientific text aloud!
After completing the reading, students get into groups of three to four. The students go around, each sharing a connection to the CCC. Each student is required to share at least two connections they made to the "Energy and Matter" crosscutting concept (there are a lot to be made in this reading!).
In this lab, students will test various food types for carbohydrates (sugar and starch), lipids, and proteins. After testing and collecting data, students analyze the data to determine how the function of the food in the living organism ties to its composition (structure)
Prior to the lab, I prepare put all of the food types that will be tested for carbohydrates, lipids, and proteins in beakers. I use about 300 mL of each for 4 classes. I place labeled eyedroppers in each beaker. I keep all of the beakers together at a central station that students will return to fill their test tubes at with each test. The food types include:
**To prepare the fish, potato, and spinach, cut them up into pieces and add them to a blender with water to liquefy them. I had an old blender donated to my classroom and I use that every year. I know you are probably grimacing at the idea of liquefying fish, but it is well worth it for the benefit of this lab.
I set up one station for each group. This station should include:
Have the students follow the procedure. Emphasize to follow the directions carefully for safety!
Test for Lipids: Step 5 is in bold to emphasize this to your students. Adding the substances to the test tube takes the longest amount of time in this lab. By saving the "food" in their test tube after the lipid test, they can eliminate having to refill and clean their tubes.
The Sugar Test: Please note that the items in bold are safety precautions. It is important to follow through with these!
Check out how this test works:
Completed Test Tube Rack:
Test for Protein:
Test for Carbohydrates (Starch):
After compiling all of their data, have students complete the lab questions.
To close, discuss the lab questions as a class. Below are some pieces of student work that can give you some insight into what the students discuss for each question:
Discussion Question #1: Identify which food types were the highest for each type of molecule.
Students find that potatoes are the highest in starch, apple juice is the highest in sugar, fish and eggs are the highest in proteins, and egg whites are the highest in lipids.
Discussion Question #2: Did water contain any of the molecules you tested today? Why did we choose to test water?
Discussion Question #3: Analyze the data for sugars and starches. Why did the food types that test high in these molecules?
Students should recognize that carbohydrates are used as immediate and stored energy in cells. Students discuss how the apple is the fruit of the plant and as the fruit is used in reproduction (seeds), it would need lots of energy. Also, they explain that potatoes are roots and are food storage organs. They explain that because they are underground they do not go through photosynthesis so they need to store food as starch. In addition, they explain that spinach would have sugars as it is a leaf that goes through photosynthesis, producing sugar.
Discussion Question #3: Analyze the data for lipids. Why did the food types that test high in these molecules?
Students explain that the egg grows a new "chicken". They connect to the idea that lipids are stored energy to the idea that growing a baby would require a lot of energy.
Discussion Question #4: Analyze the data for protein. Why did the food types that test high in these molecules?
Students note that fish had the most protein. They recognize that fish is a muscle and that proteins are used to growth, strength, and repair (all things that muscles would need).
Discussion Question #5: We didn't test for nucleic acids in this lab, but they are a common molecule found in cells. What are nucleic acids? What is their function in a cell?
Students explain that nucleic acids are found in DNA and that DNA serves as the genetic information in cells.