The Cotton-Swab Orchard: How Do Bees Turn Blossoms into Almonds?

Investigation question: In a model almond orchard, how do the arrangement of two varieties and the number of bee visits change how many blossoms receive pollen from the other variety and can set a nut?

Scientific purpose

Students build a paper orchard of 20 blossoms in two almond varieties and act as honey bees, carrying chalk 'pollen' on a cotton swab from blossom to blossom by a dice rule. They count which blossoms received pollen from the other variety, compare three planting layouts and a half-the-bees trial, and pool class data. The results become evidence for explaining cross-pollination and for evaluating the ways real growers keep pollination reliable: renting hives, planting pollinizer rows close together, supporting wild bees and planting self-fertile varieties.

Why this helps students with this chapter

Pollination happens too fast and too small to watch across a whole orchard, and it is over in a few weeks. Carrying the pollen with their own hands, students discover that a visit is not enough: the pollen has to come from a different variety, and the way the trees are planted changes how often that happens. Numbers from their own trials turn the growers' choices (rows, hives, hedgerows, self-fertile trees) into a reasoning problem instead of a fact to memorize.

Standards connections

MS-LS2-5 (practice, evaluating competing solutions for maintaining a pollination service): In q9 students judge four ways a grower could keep pollination reliable against a criterion and a constraint, using their model data and an information card. The solutions are evaluated rather than designed and the evidence comes from a simplified model, so this is practice toward the PE that Lab 3 assesses.

MS-LS2-2 (supports, a mutually beneficial interaction between pollinators and plants): The service rests on the bee-blossom mutualism from Lesson 21: bees get nectar and pollen as food, and the plants get pollen carried to other plants. The lab uses that interaction as background rather than asking students to predict interaction patterns across ecosystems.

Roles (rotate each session)

• Bee: Moves the swab one blossom per visit by the die rule, delivers pollen to the stigma, then loads pollen from the petals, and grooms the swab every fourth visit.
• Navigator: Draws the starting blossom, rolls the die, calls each move aloud, rerolls moves that would leave the orchard, and tallies visits.
• Inspector: After each trial checks every stigma label with a hand lens and calls O (other-variety color), S (own color only) or N (no chalk).
• Recorder: Fills the group data table, calculates nut set, posts results to the class table, and makes sure roles rotate so everyone is the Bee at least once.

Materials

Estimated cost: 6 to 12 per class (estimate) (an estimate; A box of 500 cotton swabs about $3, a pack of 1,000 round labels about $5 to $8, and a bucket of sidewalk chalk about $5 that lasts many classes; dice, hand lenses and printing from classroom stock. Estimated 2026 U.S. retail prices; they vary by store.)

Safety

• Chalk dust can irritate eyes and airways. Rub chalk gently, never blow on the mats, and keep dust on the tray; students with asthma can take a role that does not handle chalk.
• Cotton swabs stay out of ears, noses and mouths; use one swab per trial and throw it away afterward.
• Wash hands after the lab, because chalk on fingers ends up in eyes and on food.
• No live bees or real flowers are used. If you add real blossoms as a demonstration, check first for pollen allergies.

Teacher preparation and setup

1. Print three orchard mats per group: 20 blossom outlines in 4 rows of 5, numbered 1-20 in reading order (row 1 is the top row). Label them Layout 1 Blocks, Layout 2 Alternating rows and Layout 3 Mixed in rows, and lightly pencil B or P in each blossom using the layout key on the recording sheet.
2. Run one 20-visit trial yourself before class to check that the chalk transfers visibly from swab to label and to time a trial; aim for about 3 minutes of visits plus 2 minutes of inspection.
3. Cut and number 20 slips per group for choosing a random starting blossom, and put out the die, swabs and labels in a kit per group.
4. Draw the class data table on the board (groups down the side, the four trials across the top) so groups can post results as they finish.
5. Check for students with asthma or dust sensitivity; chalk dust is light, but they can take the Navigator or Recorder role.

Investigation design

Student procedure

1. Read the recording-sheet background and layout key, then answer q1: predict which layout will set the most nuts in 20 visits, using the bee's movement rule in your reasoning.
2. Prepare the mats. Rub chalk on the petals of each blossom in the color marked (B blue, P pink) until they are well dusted; leave the center white. Stick a fresh white label in the center of every blossom: it is that blossom's stigma.
3. Learn the visit rule. At each visit the Bee (a) presses the swab tip once on the stigma label to deliver whatever pollen it carries, then (b) rolls the swab tip once around that blossom's petals to load its pollen. After every fourth visit, the Bee wipes the swab twice across the paper towel, standing for the way bees groom much of their pollen into their pollen baskets.
4. Learn the movement rule. Draw a slip to choose the starting blossom. Before each later visit the Navigator rolls: 1 or 2 = one blossom right along the row, 3 or 4 = one blossom left along the row, 5 = up one row, 6 = down one row. If the move would leave the orchard, roll again. Revisiting a blossom counts as a visit. (Observers often report that honey bees work along a tree row more than across rows; this rule builds in that tendency.)
5. Trial 1: run 20 visits on Layout 1 (Blocks) with a new swab. The Inspector then checks every stigma and records O (shows any of the other variety's color), S (shows only its own variety's color) or N (no chalk). Only an O blossom can set a nut.
6. Rotate roles. Replace all 20 stigma labels, re-dust any faint petals, and run Trial 2 on Layout 2 (Alternating rows) and Trial 3 on Layout 3 (Mixed in rows), 20 visits each with a new swab each time.
7. Trial 4, half the bees: run Layout 2 again with only 10 visits. For every trial calculate nut set (%) = number of O blossoms / 20 x 100.
8. Post your four nut-set results on the class table, copy the class data, compute the class mean for each trial, plot the means on the graph, and answer q2-q5 as a group.
9. Clean up: peel off and discard labels and swabs, fold the chalk dust into the newspaper and throw it away, wipe trays, and wash hands. Answer the analysis questions individually in class or for homework.

Expected observations

• Predicted pattern, not yet confirmed in a classroom (from running the same rules many times on a computer with assumed chalk carryover): Blocks lowest, about 0-6 of 20 blossoms with other-variety pollen in 20 visits (class mean near 15 percent); Alternating rows about 4-9 of 20 (near 35 percent); Mixed in rows about 7-12 of 20 (near 45 percent).
• Halving the visits on alternating rows (Trial 4) roughly halves nut set, to about 1-5 of 20 blossoms (near 17 percent).
• Blocks produce the most S blossoms (own pollen only), often 4 to 9: the bee visits plenty of blossoms but carries the wrong pollen. Mixed rows produce almost none.
• No layout comes close to 100 percent in 20 visits, because the bee revisits some blossoms and never reaches others; many blossoms stay N.
• Single-group results vary widely from trial to trial; the class means separate the layouts much more clearly than any one group's numbers.

Likely difficulties

• Loading before delivering. The order matters: press the stigma first (deliver), then roll the petals (load). Reversing it gives every stigma its own color first and blurs the results.
• Chalk that is too faint to see on the swab, or petals so heavily chalked that dust falls onto the labels. Re-dust lightly between trials and tap off loose dust.
• Forgetting to groom every fourth visit, which lets pollen carry over for many visits and makes the layouts look more alike.
• Steering the bee instead of following the die, often toward the other color. The Navigator calls every roll aloud.
• Counting a fingerprint smudge as pollen. Inspectors should look for chalk in the center of the label where the swab pressed.

Structured debrief

1. Post the class means and ask what pattern holds across groups even though single trials varied. In the expected pattern, mixed rows set the most nuts, blocks the fewest, and halving the visits cut nut set roughly in half. Ask groups to explain the order with the movement rule: crossing to the other variety happens only at the middle boundary in blocks, on up-or-down moves in alternating rows, and on every move in mixed rows.
2. Spend time on the S blossoms. Blocks produce many blossoms that were visited and carry pollen but cannot set a nut, because the pollen is their own variety's. That is self-incompatibility, and it is why growers plant pollinizer varieties and why self-fertile varieties need fewer bees.
3. Connect to the bee trucks: renting hives is a technological substitute for a pollination service the landscape no longer provides in full. Run a quick gallery of q9 answers and look for groups that combined a fast fix (more hives) with a slow one (hedgerows or self-fertile trees).
4. Close on q7 and q10: the model's best layout is not the real growers' choice, because harvest timing, cost and real bee behavior are criteria too, and a model with one swab and a die leaves out weather, thousands of bees and the biology of the tree.

Recording sheet: what students fill in

Lab 1 recording sheet: The Cotton-Swab Orchard

Most almond varieties cannot be fertilized by pollen from their own variety. A blossom can set a nut only if a pollinator brings pollen from a different, compatible variety. In this model, blue (B) blossoms are the main variety (call it Nonpareil, the most widely planted variety) and pink (P) blossoms are a pollinizer variety planted to supply compatible pollen. The chalk on the petals is pollen, the white label in the center is the stigma, and your cotton swab is one honey bee.

Analysis questions: answer key

Individual evidence of learning

Each student submits the group and class data tables, the class graph, and individual answers to q6-q11. q3 and q6 show understanding of cross-pollination and why the layouts differ; q8 is the calculation; q9 is the evaluation of competing solutions with a named criterion and constraint; q10 and q11 show model critique and why pollination depends on habitat.

Assessment criteria

Accessibility adaptations

• Print large-format mats with B and P printed inside every blossom, and add a strip of masking tape on pink blossoms so they can be found by touch.
• For limited fine-motor control, use foam makeup swabs, or let a partner move the swab while the student directs and calls the rolls as Navigator.
• Give a nut-set conversion strip (1 blossom = 5 percent, 2 = 10 percent, and so on) and a percent-change frame: (new - old) / old x 100.
• Offer sentence frames for q6 and q9: 'In the ___ layout, the bee crosses to the other variety when ___, so ___' and 'I would combine ___ and ___ because ___; this meets the criterion ___ within the constraint ___.'

Low-cost alternative

With no chalk or labels, run the same dice rule with a sticky note as the bee: the Bee writes the variety of the last blossom visited on the note, and the Inspector marks O on a blossom whenever the note arriving there names the other variety. The data and reasoning stay the same, but students lose the hands-on pollen transfer and the carryover of pollen across several visits. A floor version with 20 students holding blue and pink cards in a 4-by-5 grid works the same way.

Model limitations

This activity has not been physically tested by the authors, and the expected pattern comes from a computer run of the same rules with an assumed amount of chalk carryover, so classroom numbers may differ. Chalk is not pollen: real pollen sticks to branched hairs, is groomed into pollen baskets and loses viability over hours. One swab stands for one bee, while a real orchard has thousands of bees working for weeks and each tree carries thousands of blossoms. The die rule simplifies bee movement; real bees choose flowers by their reward and stop flying in cold, wet or windy weather. Real nut set also depends on pollen compatibility, bloom overlap, frost, water and nutrients, and many pollinated blossoms still drop. Use the model to compare layouts and visit numbers, not to predict a real orchard's yield.

Teacher notes

Check that O + S + N = 20 in every row of the group table before accepting it. The predicted numbers in the expected observations come from a computer run of the rules and are not classroom-tested; if your class's means do not separate the layouts, look first at whether groups delivered before loading and groomed every fourth visit. For q4, use the class's own means. q9 has no single right answer; grade the reasoning with the criteria. If time runs short, assign q6-q11 for homework and use slide 14 the next day to review the S blossoms.