The theory of evolution and its power to explain “the diversity and unity of life on Earth” is a core life science idea (NRC 2012). While genetic mechanisms of inheritance are taught during upper elementary and middle school, the foundations are laid when young children observe and describe variation within and among related groups and connect parent and offspring traits. In the previous edition of Science and Children, we described lessons on recognizing and describing variation in plants (Feller, Halpern, and Underwood 2023). In this article, we describe lessons to develop student ideas about what causes that variation, including inheritance of traits. While this set of lessons was used with a second-grade class, the lessons can develop the understandings that build toward first-grade through third-grade performance expectations. These garden-based activities were made flexible and manageable for the teacher by combining use of individual student mini-gardens in the classroom with work in an outdoor garden.

Although plants can be easy to use in teaching, they present a special challenge when teaching inheritance. The youngest plant life-stages (seeds and seedlings) look different from adult plants, and different types of adult plants can have seedlings that look relatively similar, making direct observation of parent-offspring similarity difficult. One might think that this would make it hard to use plants to get students excited about thinking about inheritance; this was a particular concern for us because the donated seeds we had available were a mix of vegetables in the mustard family, all of which look extremely similar as seeds and seedlings. However, in the lessons we describe here, we found that the smaller-than-expected variation among young plant stages made students look more closely and provoked excellent questions that inspired authentic scientific inquiry. A powerful modification of these lessons would be to start with a more varied selection of seeds. The mustards used all have similar seed and seedling traits. An alternative mix could include peas, beans, and corn; these larger seeds with sturdier seedlings and thick stems exhibit different cotyledon and true leaf traits early enough to observe inherited differences more quickly.

Lesson 1: Why Do Plants Look the Way They Do?

Connecting Shared Traits to Inheritance

Even young students have some knowledge and (mis)conceptions about why individuals have certain traits. This lesson focused on uncovering their ideas about inheritance and connecting them to similarities and differences among adult plants that they had already observed. Now we wanted to guide them toward considering why plants look the way they do using the anchoring phenomenon of the notable similarities within family groups. Students observed photographs of plant and animal family groups: a spotted sow with a litter of variously spotted piglets and an oak tree with acorns and seedlings at its base. Students described the pigs and suggested that they saw a mama with her babies. When asked why they thought so, they mentioned that some of the small pigs were nursing, that baby pigs would stay near their mother, that the pigs were all spotted, and that baby animals will look like their parents. Students were familiar with acorns falling from oaks and thought those acorns would also grow into oaks. Ms. Sky read aloud “From Seed to Plant” (Gibbons 1991), which follows plant life cycles from seed to adult and back again. Ms. Sky reminded students of their previous observations of vegetable plants. When asked why kale plants look more like kale plants than like spinach plants, students said plants will look like their parents and kale parents make kale seeds. While the assessment boundary through third grade does not include genetic mechanisms of inheritance, this ability to describe observations of patterns of traits in parents and young is foundational to their understanding of inheritance (NGSS Lead States 2013). With this foundation in the phenomenon, we began a series of lessons focused on the investigative question, how can we tell if plants are in a family group?

Lesson 2: Setting Up Mini-Gardens

Connecting Expected and Observed Variation in Seed Traits

The first lesson investigating our question focused on seeds. Students explored variation in our donated mix of vegetable seeds and planted their individual mini-gardens so they could later look for variation in seedlings. Ms. Sky first gave the students a mix of seeds from five different vegetables in the mustard family—kale, broccoli, cauliflower, arugula, and mustard—and showed them photos of the mature plants. Students predicted they would be able to distinguish different kinds of seeds. In trying to sort the seeds, students noted they were all small, round, and shades of tan, but found it was challenging to separate them into distinct groups. Ms. Sky asked students if they thought they would be able to recognize the different types of plants as seedlings. Most students predicted that they would see variation in traits like leaf shape, plant size, and stem width (which they had studied before, see Feller, Halpern, and Underwood 2023) because the adults looked different. Here students observed that the amount of variation might differ at different stages in a plant life cycle. The students each planted their seeds in a personal “mini-garden” (clear 4×5 inch plastic clamshell containers with coir fiber pellets instead of soil). The class planned to check the seedlings regularly to see if they could observe differences among the plants based on their known family groups.

The mini-gardens were a wonderful tool for making garden learning flexible and manageable. Students can select their seeds and explore the effects of environmental conditions. If used across the entire year, they could even observe the offspring of particular plant parents; plants with relatively short life cycles (such as peas, beans, and cilantro) could be started from seed in the mini-garden, then transplanted to an in-ground garden or pot until seeds develop, which can be planted again. Students could grow, observe, and eat vegetables quickly and safely at the same time as the less controlled and more time-intensive in-ground garden was getting started. In addition, mini-gardens can allow for fast pivots when unexpected problems or opportunities arise.

Lesson 3: Building and Using a Conceptual Model

Recognizing Traits Through the Life Cycle

To build both conceptual understanding and skills related to identifying family groups of plants, Ms. Sky adapted an activity often used to teach seed anatomy (dissecting soaked lima beans) to help students recognize seed traits and connect their observations of seeds to their prior observations of parent-offspring resemblance. Ms. Sky told the students that she chose the lima seed because it is large and easy to see, but that if they had stronger magnifiers, it would be possible to look into the small seeds they planted in their mini-gardens. Ms. Sky added dilute food coloring to highlight the plant embryo with the cotyledons, or seed leaves, and the first “true leaves,” which look more like adult leaves than the cotyledons. Ms. Sky asked the students to notice the shape of the “true leaves” and showed them pictures of adult bean plants to demonstrate the similarity. Then she asked them what they thought the tiny leaves inside a broccoli seed would look like; students said they would look like broccoli leaves, only much smaller. The students were able to use the bean seed as a mental model for understanding other plant seeds too small to observe directly.

At the end of this class, students observed the germinating seeds in their mini-gardens. They recorded observations, labeling seedling parts including cotyledons and true leaves, measuring seedling height, noting any differences among seedlings, and recording their questions and predictions using the ABCDE drawing approach (“accurate, big, colorful, detailed, and explained;” see Feller, Halpern, and Underwood 2023; Figure 1). To differentiate learning for students, Ms. Sky used a variety of strategies. All students received instructions verbally, and lesson tasks, diagrams, and key points from discussions were written on a whiteboard. The teacher modeled activities in front of the class, especially when using new materials. In addition, students with identified needs for writing support received sentence stems and key vocabulary words on a small whiteboard at their seat. For students who required additional help to set up a journal format from the model, Ms. Sky worked with them one-to-one. While all students received journals and the expectation to use them, when a student’s written work was minimal or absent, Ms. Sky used group and individual discussions to capture student observations and questions on whiteboards. Work in individual journals provided formative assessments throughout the lessons. Student diagrams and questions were checked for understanding during and after lessons to gain insight into gaps in student understanding and those insights used to help fill gaps or correct misconceptions. This allowed students to self-assess their own understanding, and the teacher to identify students who needed extra help.

Lesson 4: Comparing Predictions and Observations About Seedlings

In this lesson, the students used science communication to refine and compare observations and predictions about their seedlings (answering the investigative question). The students did a “museum walk” looking at each other’s drawings of seedlings and sharing their observations from lesson 3. Students were encouraged by seeing classmates’ detailed observations to look more closely at their own seedlings (Figure 2). There were some differences in height, cotyledon color, and stem color between the seedlings, but otherwise the seedlings looked much the same. Students suggested that since they knew some of these plants would look different once they were fully grown, most of the differences must come after plants developed their true leaves, flowers, and fruits. Ms. Sky helped all the students see some differences in cotyledon and true leaf shapes in their mini-gardens (Figure 3).

Lesson 5: Open-Ended Exploration

Recognizing and Applying Patterns and Building Skills in Scientific Practices

The objective for the final weeks of the class was to give students, who now had a lot of background knowledge on plant parts, life cycles, and variation within and among groups, a chance to apply this knowledge to ask their own questions about the resemblance between related and unrelated groups of seeds and plants and figure out how to answer them. In our final classroom session for this project, Ms. Sky led the students in exploring their questions about variation among plants. Most of their questions were about what contributed to the variation they observed. They wondered about inheritance and how seedlings might come to look like adults. As an outgrowth of observations of seedling height in their mini-gardens, students also had many questions about how environmental factors might affect seedling traits. With teacher prompting, they began to make predictions and suggest experiments. Some students noticed differences in seedling height depending on how close seedlings were to the edge of the container. Students had planted seeds very thickly and the seedlings emerged as a dense thicket. Students began to discuss the ideas that height differences between sprouts could be due to crowding or to their plant type. Ms. Sky asked if there was a way to test this. Students suggested that they could plant only a few widely spaced seeds in the mini-gardens, or that they could plant in an outside garden where there is more space. If there was time in the school year, or if working with older students, this would have been an opportunity to integrate performance expectation 3-LS3-2 (Use evidence to support the explanation that traits can be influenced by the environment). Students were, at this point, working toward this understanding.

Next, students planted seeds in their outdoor garden. They focused on inherited differences among plant families by planting “stir fry greens” (mustard family), radishes and arugula (mustard family), lettuce mix (sunflower family), okra (mallow family), carrots (parsley family), sesame (sesame family), and loofah (squash family). As a group they examined the seeds they planted and noted the variety within and among families. Lettuce and loofah seeds were clearly distinct, but students had a harder time distinguishing between types of lettuce and types of mustards. Students wondered if seeds that look very similar would make seedlings that look very similar. Several students predicted they would see more variation once true leaves emerged, remembering that our mini-garden seeds were very similar even though the adult plants would be different. Some students said different kinds of lettuce or mustard would look more similar to each other than lettuce would look like mustard. The class labelled plantings carefully so that they could continue to observe their growth. Over the next few lessons, students observed the seedlings daily but informally. While carefully labelled rows allowed students to keep track of the different vegetable types, students still faced the challenge of differentiating weed seedlings from vegetables. They noted that seedlings look very much alike. Students saw some variation, though (Figure 4), and suggested using their mini-gardens to plant the seeds used in the garden to observe the seedling characteristics of different types of plants to help distinguish them from weeds. Ms. Sky reinforced the idea that they had recognized something important—that there was a pattern to the variation in plant traits, and that they could use what they had learned to help them identify plant types. A summative assessment and rubric are included in the supplementary materials that could be used to assess understanding at the end of this unit (see Supplemental Resources).

Reflections

As a result of this set of lessons, the students understood that plants have offspring and that those offspring grow to look like their parents even though the youngest plants may look somewhat different than their parents. They observed patterns of similarity across different types of vegetables in their life cycles and basic form, and they observed that individuals of a particular plant type are similar, but not identical. They also connected environmental conditions (e.g., crowding) to differences among plants.

This set of lessons allowed students to explore the disciplinary core ideas of LS3. A: Inheritance of Traits, and LS3. B: Variation of Traits, the crosscutting concepts of Patterns, Scale, Proportion and Quantity, and the science practices of Constructing Explanations and Designing Solutions, Developing and Using Models, and Obtaining, Evaluating, and Communicating Information. These students are building toward their eventual understanding of inheritance and evolution. We implemented these lessons in a second-grade class, but they can span first-grade through third-grade performance expectations. We believe this will continue to be important as teachers contend with widening gaps in student knowledge and skills due to COVID-19 interruptions to learning.

This set of lessons also sparked the development of authentic independent lines of inquiry. Many further explorations came out of our mini-garden and garden work. Students asked to plant seeds from their lunches, started plants from cuttings, became excited about growing mini-gardens at home, and ended the year with lots of ideas of how to plan a fall garden on their return to school. The seeds were planted!

Supplemental Resources

Download assessment and rubric at https://bit.ly/3URuxRy.

Acknowledgments

We are grateful to the other participants in the “Garden Science” seminar at FSU, which was the inspiration for these lessons: Todd Bevis, Dr. Meredith Cenzer, Dr. Anna Grinath, Henry Gwyn, Dr. Andrew Merwin, Reo Morris, Becky Pengelley, Brendan Scherer, Lindsey Stawowy, and Burgen Schwartz. We thank Cornerstone Learning Community Director Jason Flom for allowing us to test these lessons with students. This work was supported by NSF DEB-1456237 to Nora Underwood and Brian Inouye, and NSF DEB-14559911 to Stacey Halpern.

Sky Feller (sfeller@cornerstonelc.com) is a science and gardening teacher at Cornerstone Learning Community in Tallahassee, Florida. Stacey Halpern is a professor of biology at Pacific University in Forest Grove, Oregon. Nora Underwood is a professor of biological science at Florida State University in Tallahassee.