Plant Specialization: Which Organs Store Food?

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Students will be able to provide evidence that plants make and store food.

Big Idea

Students use iodine to determine which plant organs store food as starch!

Introduction and Connection to the NGSS and Common Core

This lesson includes a wide variety of strategies for student learning.  Students use the Crosscutting Concepts to critically think about text, they add iodine to plant organs to provide evidence of food storage, and they utilize discussion techniques to make meaning from the patterns they find in their data.

Specifically, this lesson is designed to address the following NGSS and Common Core Standards:

MS-LS1-3 Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

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.RST.6-8.10  By the end of grade 8, read and comprehend science/technical texts in the grades 6-8 text complexity band independently and proficiently.

CCSS.ELA-LITERACY.WHST.6-8.1.B  Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources.

Science and Engineering Practices:

SP1 Asking Questions and Defining Problems:  Students at any grade level should be able to ask questions of each other about the texts they read, the features of the phenomena they observe, and the conclusions they draw from their models or scientific investigations.

SP7 Engage in Argument from Evidence:  Respectfully provide and receive critiques about one’s explanations, procedures, models, and questions by citing relevant evidence and posing and responding to questions that elicit pertinent elaboration and detail. 

Crosscutting Concepts:

Patterns:  Observed patterns in nature guide organization and classification and prompt questions about relationships and causes underlying them.

Structure and Function:  The way an object is shaped or structured determines many of its properties and functions.

Connecting to the Essential Question: What are you supposed to learn today?

5 minutes

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 5 (I can develop models to demonstrate that organisms are made up of tissues, organs and organ systems that have specific jobs).  As the students this is the first lesson focusing on this learning target, 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). Remind them that it is understandable that they might be at a 1 or 2 at this point.  This is their first exposure to this material!  Learning is about growth and the path to mastery.  It is not expected that the skill be mastered today.  

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.

Mini Lesson: Pulling Meaning From Text Using the Crosscutting Concepts

25 minutes

Students read the "Cell Organization" and climb the "Ladder of Discourse".  The "Ladder of Discourse" is a strategy I use in my class to help students think critically as they read.  For middle school students, informational reading can just become words on a page.  The "Ladder of Discourse" is a way to help students recognize what they should be thinking about as they read so that they can gain an understanding of the text.  The levels of the "Ladder of Discourse" are "Tweets" (text to self connections), "Huh?'s"(questions or concepts they do not understand), "Found It" (finding answers to questions through context clues or finding science answers), and "Discourse" (combining ideas to think beyond the text).  The resource "Ladder of Discourse: Description of Rungs" provides background about the "rungs" students use when reading.  

As students engage in discourse with the text, they connect to the NGSS Crosscutting Concepts.  For more details about this process, check out these two lessons:  Microscope Mania and pHun with Phenolphthalein.

Below is an example of how students document their "Ladder of Discourse" as they read.

Ladder of Discourse Student Examples:

Tweet: The student makes a connection between a science concept and something she connects to in her life.  In the example above, the student notes that "her friend broke two bones in her leg".

Huh?:  This student asks the question when getting to the word "nervous system", "What does this do?".

Found it!:  Found it can be a student finding the answer to a question using context clues or in connecting to science vocabulary.  For example, the student when reading the word "specialization", used her prior knowledge to determine that the word related to "helping form a function for a system".

Discourse:  Each of these connect to a specific NGSS Crosscutting Concept.  I only used a few examples here; but each student connected to a different crosscutting concepts in their reading.  However, with this text, the most common connection students make is to "Systems and System Models".

System and System Models:

Energy and Matter:

Food Storage Organs Lab

30 minutes

Provide students with the Plants Store Food Investigation Lab Sheet.  This lab document is one that a local school district created (Kent ISD).  While I do not have the students answer the "essay" question at the bottom of the document, you certainly could.  I use the data collected in the data table to promote discussion later in the lesson.  So, my students simply complete the data table.

Before class, I cut up into small pieces the plant organs included in the lab document (corn, lima beans, potatoes, carrots, etc.).  You really don't need many!  Each group only needs a small piece to collect the data from.  This lab could get expensive if you had to buy large quantities of each vegetable.  I have even asked students to help donate a carrot or onion to help.  Or, I have planned stir fry for dinner for my family and just kept a few pieces of each vegetable back for the lab!

I place each type of plant on a plate and provide each group with a tray/plate and one glass bottle with dropper full of iodine.

First, we discuss the background information from the lab sheet.  We discuss how we have already learned that plants produce glucose through photosynthesis.  I introduce the idea that if plants do not use the glucose for immediate energy, they can store it in long chains of sugars, called starches. I explain that we call glucose produced by photosynthesis simple carbohydrates and the long chains of sugars, or starches, complex carbohydrates.   

Then, I have them connect to a couple of concepts that they have been introduced to prior to this lab.  First, I connect to the reading they just explored by stating that just as we do, plants have organs that perform functions to support life as well.  Instead of a heart or a brain, plants have organs such as seeds, roots, stems, leaves, fruits, and flowers.  I then ask them, "What would you expect if you looked at the structure of these plant organs?"  Students explain that "the structure of the organ would be related to their function" (a concept we have been addressing throughout the cells unit).  I provide further detail to explain that structure doesn't always mean size or shape, it also can be what it is made of, or its composition.  I explain that certain plant organs have the function of storing food for the plant and in the lab today, we will collect evidence to determine which organs are food storage organs for plants.

In order to collect the evidence, I explain that iodine (or Lugol's solution) is a substance that turns a dark purple when in the presence of starch.  I explain that to many of them, it may be so dark it appears black.  In addition, I emphasize that only a drop of iodine is required to see the color change. (Without this prompt, students will inevitably overuse your iodine!)  The last tip I provide my students with when completing this lab is to try to get into the tissue of the organ.  For example, when dropping the iodine on the corn, if you drop it on the "skin", the iodine will just roll off.  Cutting the plants in a way that exposes the inside cross section is helpful to the students.

Students find positive tests for corn, lima beans, potatoes, and carrots.  Some identify a slight change in tomatoes.  In other words, the roots and seeds show up as food storage organs!  As students work, as them to find patterns in their data and to provide evidence of their findings.

Closure: Student Data and Discussion

15 minutes

After completing the lab, the discussion following is key to building deep understanding.  The questions below ask students to look at patterns and make connections to structure/function relationships that they have never considered before!  This critical thinking discussion will require the students to combine their prior knowledge about cells to develop new ideas about the structure of cells as well as structure function relationships.  

Plants Store Food Discussion

1.  Analyze your data.  What patterns do you see?

2.  Why do you think that the organs that tested positive for starch are food storage organs?  In other words, why would they be the organs that would need to store food?

3.  I’m confused.  I know that leaves go through photosynthesis.  Why didn’t they have starch then?

4.  From our data, we can see that every cell contains different molecules based on their function.  Cells also contain different amounts of organelles based on their functions.  We know that plant cells contain chloroplasts, cells walls, and large central vacuoles.  What organs in a plant might contain a varying amount or size of these organelles based on their function?


5.  Animal cells also are specialized and contain a varying amount of organelles based on their function.  Some of the cells in our body contain thousands of mitochondria while others contain very few.  Which organs in our body might contain a large number of mitochondria based on their function?  Why?