Today students will dissect several flowers and compare their structures to determine how botanists classify monocots and dicots. First, students will dissect a Peruvian lily which can be easily purchased from any supermarket. Students learn the parts of the angiosperm flower during the first dissection. Next, students will dissect the flower they brought to class in a second dissection. Depending on what students brought from home, they might dissect a monocot or dicot. Students can experience the diversity seen throughout the angiosperms. Finally, students will explore several theories that explain how flowers led to the success of angiosperms. Here is an overview of what they will learn today.
Depending of the time of year, each student should bring a flower to school. Have students briefly show their flowers and describe where it was collected. Students should complete this graphic organizer as everyone shares. (Note: Students should not complete the final column of the graphic organizer. This will be done later in the period.)
In their lab notebooks, have students brainstorm responses to the question:
What is the reason plants have flowers?
(Typical student answers: They attract pollinators. They help them reproduce.)
Why are there so many different kinds of flowers?
(Typical student answers: People selectively breed flowers to make certain colors or certain sizes. In nature, certain plants were better adapted to certain environmental conditions. However, most students will not have any ideas why there are so many different kinds of flowers.)
Students will dissect a flower from the lily order to investigate its structures.
Materials needed for each lab group of two:
Each lab group should receive one flower and dissecting equipment. In their lab notebook, they should sketch the external structures on the plant. At this point in the lab, they should not try to label any portion of the flower. They should simply note where they believe new tissue arises (as they did in the leaf lab the previous day). After students have examined the outer portion of the flower, they should begin by removing several petals. Students should sketch the structures that they see in their lab notebook or provided graphic organizer.
Students should identify the following structures: stamen, fllament, anther, plan, pistil, stigma, style.
Next, students should remove the rest of the petals and count the number that the flower has.
Students should write their responses in their lab notebook or provided graphic organizer.
Using forceps, have students removed the stamen (filament and anthers) of the plant.
Using a scalpel, have students bisect the female portion of the flower (style and ovary). Students should make a sketch in their lab notebook. Using the magnifying glass, have students look closely at the ovary for possible ovules. Students should sketch what they see. Have students set these structures aside for later comparison.
Students should select the flowers that they brought to class today. They should dissect them using the same methodology that they used in the Alstroemeria dissection.
Next, students should construct a chart in their lab notebook (or use the attached graphic organizer). They should summarize the results of both dissections.
When all are done with their dissections, student should share their findings of the dissection.
Poll the student groups to determine how many of each plant structure (sepals, petals, stamen, ovules) each of their plants had. Record their findings on the board.
Next, ask students if they notice any relationships between seemingly unrelated plant species. In their lab groups ask they to arrange the plants into two groups. Give students several minutes to do this then bring them back together and ask them to share what criteria they used to determine the two groups.
Introduce the terms monocot and dicot and explain the criteria that scientists use in these grouping.
Students should consider the number of flower parts each flowers has and fill out the final column of graphic organizer from the beginning of the period.
(Note: Monocots have floral parts in multiples of three, while dicots have floral parts in multiple of four or five.)
Next, ask students what benefit flowers might provide plants. Discuss the purpose of flowers and how flowers are modified to attach certain types of pollinators. Have students consider several flowers and brainstorm what type of pollinators would be attracted to certain flowers. Discuss the various types of pollination.