Academic journal article Science Scope

Using Math to Support Claims about Wind-Dispersed Seeds

Academic journal article Science Scope

Using Math to Support Claims about Wind-Dispersed Seeds

Article excerpt

[ILLUSTRATION OMITTED]

When learning how to support claims, students see that evidence is often data expressed in graphical form. In this lab exercise, students make a claim about factors influencing the travel distance of wind-dispersed seeds and then use the engineering design process to create a fruit that will disperse farthest from the parent tree under windy conditions. Students hypothesize that fruits with a smaller weight or a larger surface area will have an increased dispersal distance. They then test this hypothesis and gather data as evidence to support their claim.

The investigation

Flowering plants (or angiosperms) are particularly diverse, with over 350,000 species identified. These plants all have flowers (although some are short-lived and inconspicuous) and fruits (although some are dry rather than fleshy and sweet). In flowering plants, an embryo is encased in a protective outer coat, the seed, which is enclosed within the fruit. Usually, plants that use wind for seed dispersal have seeds that are small (more lightweight) or have structures that catch the wind. In this investigation, adapted from Rice and Russel (2001), students explore how the size and shape of fruits influence their seeds' ability to be dispersed by wind. Students are then challenged to design a fruit that will disperse its seeds the farthest. Students design, test, and modify their own model fruit (containing the seed) by dropping it in front of a fan and measuring the distance its seeds traveled away from the drop point.

Safety considerations

Remind students that they may not eat anything in the science classroom or lab, including edible fruits. I usually avoid peanuts but often do include tree nuts, so determine beforehand whether students have allergies, and make sure they just look at, not touch, the fruits. Students with allergies can record data or be in charge of the "drop zone." Making model fruits out of craft supplies is typically fine for all students. When using the electric fan, caution students to watch out for cords, and remind them to not stick fingers or objects into the fan.

Engage

This investigation is best done over three days in springtime, when fresh flowers are available from a variety of local trees. Students can thus study some of the more easily missed flowers (such as those from maple and oak trees). I also purchase lilies from the local grocery store. These large flowers have easily identifiable parts, which helps with discussions about "perfect" flowers (which have both stamens and carpels; i.e., lilies and peaches), monoecious plants (which have separate male and female flowers on the same plant; i.e., oaks), dioecious plants (which have male flowers on a male plant and female flowers on female plants; i.e., holly), and modes of pollination. I also bring in a variety of fruits, both traditional (e.g., apples, cherries, lemons) and nontraditional (e.g., pecans, walnuts, green beans, bell peppers, cucumbers, sugar snaps). I cut the fruits to best show the seeds (e.g., longitudinally for green beans, horizontally for apples). I spread these out on a side counter so that students can see the differences; there are always some students who have never seen some of the fruits before, so it is best to have visuals. Most of these fruits can be bought at the grocery store. We discuss fruit types (e.g., lightweight or with "wings" for wind, fleshy and sweet for animal ingestion), together predict their modes of seed dispersal, and fill out a worksheet with this information (see Online Supplemental Materials).

Explore

The following day, students make their model fruits. Each group of four students receives a plastic shoebox filled with scissors, tape, and craft supplies (e.g., paper, glue, pipe cleaners, craft feathers, foam packing, index cards, toothpicks, cotton balls, resealable baggies, straws, string, tin foil). Each group also has at its table a fan, meter stick, balance, and graph paper. …

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