"Each year my fourth and fifth graders brainstorm a variety of plant foods, then choose one type as a focus for in-depth investigations," reports Brighton, MA, teacher Rita Holder. "This year, citrus fruits inspired their curiosity." The unit began with students exploring a medley of citrus fruits - orange, tangerine, grapefruit, citron, lemon, ugli fruit - and several citrus fruit plants donated by a local plant shop. Students' initial observations and comparisons yielded a range of questions and ideas about what citrus fruits have in common, Rita reports. They observed, for instance, that most contained a juicy pulp (so they organized their fruits from least to most juicy), similar hard rinds (though thicknesses varied), and distinct segments. "Students had read in free industry literature that Florida oranges were juicier than California oranges," says Rita. "This prompted them to compare the two types first by tasting, then squeezing and measuring the juice. They were surprised and somewhat pleased that their findings conflicted with the claims," she adds.
Taste tests led students to agree that citrus fruits were rather sour, reports Rita, which prompted their interest in testing the fruits for acidity. Using the Lawrence Hall of Science GEMS Teacher's Guide, Cabbages and Chemistry, her young scientists created a pH indicator with red cabbage dye, then used it to compare citrus fruit acidity with that of vinegar and other substances. Students also decided to test each fruit for its vitamin C content. Using indophenol solution (which undergoes a series of color changes as vitamin C is added to it) purchased from a science supplier and the GEMS Teacher's Guide, Vitamin C Testing, they were able to compare the relative vitamin C contents of fruits in their collection.
Wondering if they could grow their own citrus plants, students collected seeds from grapefruits, tangerines, oranges, lemons, and limes, then planted them 1/2 inch deep in different types of containers, and placed them in the GrowLab. "Although most took about a month to sprout, we now have a small citrus orchard," says Rita. When some students wondered how new citrus plants could grow from seedless fruits, they researched this topic, then invited a local plant store owner to demonstrate how to graft citrus plants.
"As our citrus gallery sat on the table, we began to notice that some fruits were molding while others remained healthy," describes Rita. "This prompted us to wonder what conditions promote molding and whether we could find out by trying to create those conditions." Students placed fruits in different conditions - in covered and noncovered containers in darkness, light, warmth, and cold - to determine which factors promoted mold growth. "Despite the students' 'moldy efforts,' a couple of the fruits remained mold-free," notes Rita. "prompting further questions and a suggestion that we use our experience as a springboard for writing a mystery story!"
Throughout the unit, says Rita, students discussed health benefits of citrus as they enjoyed a daily citrus-derived snack. Challenged to consider different ways to consume these fruits, students invented their own recipes. Each student used a computer to organize the ingredients and preparation instructions in recipe form, then invited a family member to help present and serve the concoction - from citrus frappes to orange-sicles. They videotaped each presentation to provide other classes with nutrition ideas and to help students evaluate their work.
With an eye on the USDA's nutrition pyramid, each student kept a record of the five fruits and/or vegetables eaten each day for a week, using the "five a day for five days" motto being promoted by the National Cancer Institute and other organizations. "I've found this kind of in-depth food unit helps students become more aware of the health benefits and variety of fruits and vegetables," says Rita." It engages their interest because it builds and grows from their own observations and questions."