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Oct. 18, 2010

Flower Anatomy

by Science Friday Education

Click to enlarge images
Pollination is necessary for flowering plants to reproduce. Insects, wind, birds, and even some bats and other animals help in the pollination process that leads to the fertilization of flowers. Flowers that rely on other living things for pollination have adapted their anatomical structure to attract these pollinators. A flower’s color, shape and fragrance are a few examples of how its anatomy attracts animals that can serve as pollinators for it.
 
In this activity, students will discuss the various methods by which pollination can occur in flowers or plants. Students will dissect and identify the different parts of a flower, hypothesize the function of each part, and discuss the importance or relevance of each part to pollination.
 
Grade Level: 6th – 8th grade
Subject Matter: Life Science
National Standards: NS.5-8.1, NS.5-8.3
 
When pollen leaves a flower, it starts to dry out. Drying can destroy the genetic material that a grain of pollen is carrying. To combat dehydration, pollen grains have evolved a way of folding up to prevent water from leaking out. Eleni Katifori and colleagues describe the physics of pollen folding in a new paper in the Proceedings of the National Academy of Sciences.
 
Activity Materials
Flowers, such as lilies, irises, roses, daffodils, or tulips – one flower for each student.
Scalpel – one for each pair of student
Magnifying lens – one for each pair of students
Tweezers – one pair for each pair of students
Blank sheets of white paper and pencils, one of each for each student
Black construction paper, one sheet for each student
 
Vocabulary
Pollination: the transfer of pollen from a flower’s male reproductive parts to its female reproductive parts.
Fertilization: the union of male and female reproductive cells.
Sepal: the outermost part of the flower that surrounds and protects the flower bud and extends outward from the base of a flower after it has opened.
Petal: the outer parts of a flower, usually brightly colored to attract pollinators.
Pistil: the female part of the flower, which contains the stigma, style and ovary.
Stigma: the sticky part at the top of a flower’s pistil, where pollen enters the style and travels to the ovary.
Style: the slender part of a flower’s pistil, extending from the stigma to the ovary.
Ovary: the lower part of a flower’s pistil, containing its female reproductive cells.
Ovule: a small structure in the flower’s ovary that develops into a seed after fertilization.
Stamen: the male part of the flower, which contains the anther and filament.
Anther: the top part of a flower’s stamen that develops and contains pollen.
Filament: the stalk-like portion of a flower’s stamen that supports the anther.
 
What To Do
Prep: Before you present this lesson, become familiar with the anatomy of a flower by researching and viewing diagrams or images online or at the library. Teachers TalkingScience recommends that you hand out to your students printed copies of a diagram of the parts of a flower’s anatomy that are explored in this activity. Or you can draw a sketch, based on your research, on a blackboard.

1. Begin the lesson by having students watch the Science Friday video, “Pollen Origami.” Ask students to define and describe various methods of pollination. How does the anatomy of a flower support the process of pollination? Tell students that they will dissect a flower to investigate the function of each part of the flower, and how each part helps the process of pollination.

2. Hand out a blank white sheet of paper and a pencil to each student. Tell students that throughout the dissection, they will tape onto this sheet and then label the parts of the flower. Students also should write down their hypothesis of the function of each part of the flower.

3. Hand out a flower to each student. Have students count the number of sepals and petals on their flower, respectively. How do the petals or sepals feel? Based on location, shape, texture and color, what do the students think is the function of the sepals and petals?

4. Instruct students to carefully remove two or three of the sepals and petals so that they can see the inside of the flower. Have students tape and label the sepals and petals onto their sheet, and write down what they think the function of each one is, and why.

5. Tell students that firstly, they will dissect the male part of the flower. Can they guess which part of the flower is the stamen? Help students to identify and count the stamens. How many stamens are there? Why would a flower have that many stamens?

6. Hand out black construction paper, scalpels and tweezers that students can share. Have students remove one of the stamens carefully, using a scalpel and a pair of tweezers. Have students rub the top part of the stamen on their piece of black construction paper. Ask students to examine the pollen with a magnifying lens and describe what they see, including size, shape and color.

7. Have students describe the other parts of the stamen. Instruct students to remove all the stamens and tape them to the dissection sheet, labeling the anther and the filament. Students also should write down why they think the stamen is the male part of the flower, as well as the function of its individual parts.

8. Tell students that now they will dissect the female part of the flower. Have students identify the pistil and feel the top part of the stigma. Why would the stigma feel sticky?

9. Have the students use the scalpel to carefully remove the pistil and cut it in half lengthwise, so that they can examine the inside with the magnifying lens. Can they find the ovary and the ovules? Have students tape both halves of the pistil onto their dissection sheet with their hypothesis on the function of the pistil.

10. Have students compare and contrast their hypotheses on the function of each part of the flower. How are the male parts of the flower different from the female parts of the flower?

What’s Happening?
Flowers contain male and female reproductive parts. The pistil is the female part of a flower and is comprised of the stigma, style, and ovary. The sticky texture of the stigma, combined with its location at the top of the pistil, helps to attract and adhere pollen grains that may be floating in the wind or clinging to the legs of an insect. The style is the long, tube- like structure leading to the ovary, which contains the female egg cells called ovules.
 
The stamen is the male part of a flower and is comprised of the anther and filament. The anther produces pollen and the filament supports the anther. The stamens usually surround the pistil, increasing the chances of pollination.
 
Pollen grains can be transferred from the anther to the stigma in different ways, including by wind, water, insects, birds or other animals. Once the pollen grains land on the stigma, it produces a threadlike tube that travels down the style to the ovary. Then male cells from the pollen grain can fertilize the ovules and develop into seeds.
 
Topics for Science Class Discussion
• What are some adaptations of flower petals to help attract pollinators?
• What are some disadvantages facing flowers that depend on insects for pollination?
• How do non-flowering plants reproduce?
• Identify the part of the flower that will become the fruit.
 
Extended Activities and Links
Extend this activity by having students dissect different types of flowers, or by having students collect flowers from a nearby field or park. Students can observe and record the shape, size, color, and odor of these flowers. Then they can compare their similarities and differences using a Venn diagram. Can they find different species of a common flower, such as goldenrod, and record the differences?
 
Have students press their flowers after dissection by drying flowers between newspaper sheets overnight. After most of the moisture has been removed from the flower, place the flowers between two sheets of wax paper in between the pages of a phone book or any other heavy book. Allow the flowers to dry for at least two weeks. Have students frame the dried flowers and label each with its scientific name and common name, as well as the parts of the flower.
 
Take a quiz on the different parts of a flower:
http://urbanext.illinois.edu/gpe/case4/c4m1.html
 
Play this interactive game to learn more about flowers and their pollinators:
http://www.pbs.org/wgbh/nova/flower/pollinator.html
 

 

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