Academic journal article Science Scope

Let's Talk Science: Seeding Argumentation about Cells and Growth

Academic journal article Science Scope

Let's Talk Science: Seeding Argumentation about Cells and Growth

Article excerpt

What's the best way to start an argument? As teachers, we can imagine the benefits of engaging students in shared discourse about the meaning and results of data, but it's a challenge to get them started. How do we convince our students to care enough to actually argue about science? This article shows how curiosity and disagreement about the germination and growth of a seed can be used to lead students to collaboratively build understandings about growth through cell division.

To begin a scientific argument, students need a topic, a good amount of data, a difference of interpretation of the data, and some language or discourse tools. What follows is a sequence of lessons I developed to help middle-grade students learn and argue about the core concept of how a plant root grows at the cellular level. These lessons support the scientific and engineering practice of engaging in argument from evidence as laid out in the Framework for K--12 Science Education (NRC 2012) and the core life-science concept that multicellular organisms grow when individual cells expand and then divide repeatedly. This core concept is to be central in disciplinary core idea 1 of the life sciences at the middle school level in the K--12 Framework and the Next Generation Science Standards (Bybee 2013, p. 14).


This sequence of lessons has three activities that are each done in groups consisting of three students each. The groups stay the same throughout the activities. The sequence begins with an initial engagement with corn-seed germination and plant growth that elicits students' conceptions and differing ideas and launches their inquiry. This initial lesson takes three full class sessions and requires brief daily checks of plants over a period of approximately three weeks.

In the second activity, students collect data about the cellular nature of root growth using classroom microscopes and commercially prepared slides. Onion mitosis root tip slides can be purchased from online vendors (see Resources); the cost ranges from $3 to $6 for each of the 10 to 12 slides needed. The slides are stained and mounted, so they last through multiple class uses and several years. If microscopes are not available, the investigation can be done with images found online (see Micropolitan Museum in Resources).


In the third part in the sequence, students construct their understandings and come to consensus about the best explanation for how plant roots grow at the cellular level. These second and third lessons take four or five class periods each during the fourth and fifth weeks of the sequence.

I have successfully used this sequence of lessons to move the class dynamics away from a direct-instruction format to more student-led discourse. These lessons work very well during the first month of school to develop a foundation of understanding about cells and begin the essential scientific practice of engaging in argument from evidence.


Differing ideas: Seeding the argument

To begin the first activity, all students are handed two kernels of unpopped popcorn as they enter the classroom. Students can see that the kernels come from a bag of ordinary grocery-store popcorn (approximate cost is $4 for six classes of 30 students each). The question "Is a seed alive?" is written prominently on the board or otherwise displayed at the front of the classroom. Students are directed to position themselves on a line drawn across the floor of the classroom to indicate their level of agreement in response to the question. Figure 1 shows an example of how the line might look.

FIGURE 3 Role playing for group science talk

Directions: Use the phrases in Figure 4 to tell what you could say if ...

* you see something you are unsure about but think it might be important.

* you don't understand what somebody said. …

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