Introduction to floral morphology

Author: Meredith Thomsen

Overview: In this lesson the instructor first introduces students to the four floral whorls using a simple model, and leads students in creating a reference worksheet to use later with a diagram and notes about these structures. Students then examine a selection of simple flower specimens (no multiple-flower inflorescences) to gain an appreciation of the diversity among types of plants in the relative sizes, color, shape, and texture of these parts.

Lesson Concepts:

  • All flowers share the same basic structure.

  • This shared structure is inherited from a common ancestor.

  • We can identify plants and animals by their physical traits.

  • There is variation among different kinds of flowers. This variation results from four types of changes to the basic structure: parts can be multiplied, parts can be missing, parts can fuse, and parts can move.

California Science Education Standards:

  • Plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.

  • Organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.

Grade span: 6-8

Materials:
  • One model of a flower, with a water bottle as the central axis/pistil and stacking rings representing the whorls of sepals, petals, and stamens. Fisher-Price child's stacking toy would work well (see photo).

  • Flower samples for students to examine, chosen to represent a variety of forms, relative sizes and textures of sepals and petals, number of whorls, etc.

  • Hand lenses

Advanced preparation:

Duplicate sets of flowers should be prepared that can easily be passed out to student groups immediately before students are going to look at them. The "point" of each example should also be determined, to guide students' examination of the specimen.

Time: 50 minutes

Grouping: Whole class, then three or four students/group

Vocabulary: Sepals, petals, stamens, pistil, (homology).

Teaching tips:

This exercise should be followed by one in which students introduced to the idea that flowers are organized into a variety of inflorescence types. A second set of flowers representing several types of inflorescences would then be examined.

Procedure:

  1. Using the model as a visual aid, explain to students the structure of the four concentric rings of floral structures: sepals, petals, stamens, and the pistil. Have students contribute the names if they’ve learned the material before. Emphasize that the positions of these parts with respect to each other is unchanging (i.e. petals within and above the ring of sepals, stamens within and above petals, etc.). Alternate the use of the model with the drawing of a diagram on the board that the students also draw on a worksheet or in their notes.

  2. Having established the basic structure, explain that ALL flowers have this, which can be seen all the way back to the earliest flowers in the fossil record. Thus, we know that flowers have inherited this structure from an ancestral flower long ago. If you feel up to it, you can explain that such shared structures, inherited from a common ancestor, are called homologies.

  3. Then introduce the four kinds of changes that occur to the basic structure: parts can be multiplied, parts can be missing, parts can fuse, and parts can move. Have students write this list on a worksheet or in their notes. Explain that these simple changes create the amazing variety we see among different kinds of flowers.

  4. Have one student/group come up to prep table and collect a set of fresh flower specimens to bring back to their group.

  5. Guide students’ investigation of the structures of each flower in their sets by holding up each flower type in turn and directing their attention to the feature your want them to notice on each specimen (all students looking at the same thing at the same time). Students don’t have to find every part on every flower; instead, use the different specimens to illustrate different points (e.g. leafy vs. flower-like sepals, single vs. divided pistils, differences in the relative sizes of parts, radially vs. bilaterally symmetric flowers, etc.). Keep referring back to how position helps you figure out which structure is which.

  6. Close with a review of the basic structure and of the kinds of changes that occur to it. As homework, you could assign students to find a type of flower not examined in class and drawing and labeling its floral parts; students could bring in flowers and their diagrams to discuss at the start of the next class period. Alternatively, ask students to bring in flowers the next day, provide additional ones yourself, and then have students draw and label those specimens in class as an assessment.

 
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