Perfect and Imperfect Flower Dissections

Perfect and Imperfect Flower Dissections

Target Grade Level / Age Range:

7th Grade

Time:

Two 45-minute class periods

Purpose:

To identify the male and female structures of the flower, recognize their function in reproduction, and differentiate between perfect and imperfect flowers.

Materials:

  • Perfect Flowers (lilies are a good option)
  • Scalpels
  • Microscopes
  • Microscope slide
  • Cover slips
  • Glycerol
  • Large note cards
  • Packing tape
  • Corn plant that is just starting to tassel
    • Sweet corn may be the best option. It will take approximately 50 days to grow to tassel. Grow in school greenhouse if possible.
    • Pictures may be used to modify activity 2 if using a real corn plant is not feasible.

Suggested Companion Resources (books and websites)

Vocabulary (with definitions) 

  • Perfect Flower: that has male and female structures in one flower
  • Imperfect Flower: flower that does not have both male and female structures
  • Stamen: male structure of flower
  • Anther: part of stamen that contains pollen
  • Filament: part of stamen that supports anther
  • Pistil: female part of flower
  • Stigma: top of pistil, where the pollen enters
  • Style: middle section of pistil, where the pollen travels through
  • Ovary: base of the pistil that contains eggs
  • Ovule: where pollen meets the egg cell within the ovary
  • Pollen: fine, powdery substance discharged from the anther that contains the male gamete that fertilizes the ovule
  • Pollination: the process by which pollen is transferred to the female reproductive organs of a plant, thereby enabling fertilization to take place
  • Tassel: male structures of the corn plant (anther, filament)
  • Silk: part of the female structures of the corn plant (ear), including stigma and style  

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)

  • Perfect vs. Imperfect flowers
    • Perfect flowers contain both the male reproductive structures (stamen) and female reproductive structures (pistil).
      • The stamen contains the anther, which holds pollen, and the filament, which supports the anther.
      • The pistil contains the stigma, which pollen sticks to; the style, which the pollen travels through; and the ovary, where the pollen meets the egg cell and fertilization occurs.
      • Lilies are an example of a perfect flower.
      • Soybeans also have a perfect flower, but these flowers are very small and may not be the best to dissect.
        • When talking about reasons behind detasseling corn, bring up soybeans and talk about how their small, perfect flowers would make hybrid seed production different in this species.
      • Imperfect flowers contain either the male portion OR the female portion of the flower, but not both.
        • Corn is an example of a plant with imperfect flowers.
          • Corn contains two flowers: the tassel and the ear.
          • The tassel (male flower) contains the anthers and is responsible for producing pollen.
          • The silks on the ear (female flower) contain the stigma and style. Each kernel is its own ovule.
  • Complete vs. incomplete flowers
    • Complete flowers contain four flower parts: petals, sepals, stamen, and pistil.
    • Incomplete flowers are missing one or more of these four parts.
      • It is possible for a perfect flower to be incomplete, but it is not possible for an imperfect flower to be complete.
  • Detasseling
    • Like it sounds, detasseling is the act of removing the tassel from a corn plant.
    • Corn is detasseled only when the field will be used for seed corn. Corn planted for other purposes (feed, ethanol, or processing to be made into syrups, fibers, or other things) will pollinate itself, and those farmers will not detassel their crops.
    • Seed corn is detasseled to stop the plant from pollinating its own ears. When this happens, growers can plant “male rows” and “female rows” that together will make a hybrid seed.
      • The “male rows” and “female rows” will be corn plants of different varieties, or that exhibit slightly different traits. Combining them will create a hybrid.
      • Generally, there are about 3-4 female rows for every one male row. Female rows are detasseled, and male rows are left to pollinate them. Corn is pollinated by wind.
      • Hybrid plants are beneficial, because they can take positive traits from two different varieties and combine them for ultimately a better next generation. Hybrid plants also exhibit “hybrid vigor” or heterosis, which means that the first generation offspring will perform better than either parent. The same type of benefit is exhibited in animals crossed between two breeds, and is explained more thoroughly here: http://www.iowabeefcenter.org/bch/CrossbreedingGeneticsPrinciples.pdf

Interest Approach or Motivator

                Ask students what they think flowers are for. What constitutes a flower? Are they just pretty?

Procedures

Day one:

  1. Give each student group of 2 or 3 a perfect flower, a sheet of paper (to dissect the flower on), and a copy of the Flowers Student Study Sheet.
    1. This study sheet contains places for notes, and reference images. This is to aid in studying later. Let the students know that it will not be graded, but will be a helpful resource and a good place for notes.
  2. Before you hand out scalpels, explain the process of the lesson to students. Let them know that first, they will be drawing their flower and labeling structures in their science notebooks. Then, they will remove the stamen and pistil, labeling those structures, and taping them to notecards. Tell students to ask questions if they are because once pieces are cut off the flower, they cannot be put back on.
  3. Tell students to take out their notebooks and draw and label their flower. Answer questions if any arise. At this time, talk about other structures they might see on the flower. What do the petals look like? Can you see the stem? Are there sepals on this flower?
    1. Explain to the class that a flower with sepals, petals, stamens, and pistils is called complete. If the flower is missing one of those pieces, it is called incomplete. Ask students if a flower can be perfect and incomplete. The answer is yes, it can be.
  4. Tell students to remove the stamen from the flower and place it on the notecard. Then label the notecard “stamen” and label the anther and filament. 
  5. Help students make microscope slide mounts of the pollen.
    1. Have the groups place a small drop of glycerol on a clean slide, then take one of the remaining stamens and tap the anther against the slide, place a cover slip on the slide, and view it with a microscope.
    2. Alternative mounting techniques: http://www.microbehunter.com/making-mounts-of-pollen-grains/
    3. Tell students to make observations, draw illustrations and take notes in their science notebook.
  6. Then, have the groups remove the pistil from the base of the flower.
  7. Tell them to use the scalpel to cut the ovary crossways, and pinch the ovary until one or more of the ovules comes out.
    1. Tell students to observe, sketch, and take notes in their notebook.
  8. Have students place the pistil on a second notecard and label the stigma, style, ovary, and ovule. 
  9. Help students place a strip of packing tape over the flower structures securing them to the notecard.
  10. Tell students to write the names of all group members on the back of the notecard, and turn in the notecards at the end of class.

Day two:

  1. Have students observe a corn plant. Ask them questions like:
    1. Where is the flower on this plant?
    2. How can you tell these parts are the flower?
    3. What is the purpose of the corn flower, or any other flower?
  2. Have students manipulate the tassel of the plant and collect pollen to look at under the microscope.
    1. Help students create slides like in the previous class period, make observations, and record findings.
  3. Take the ear off of the corn plant and husk it. Discuss the purpose of the silk at the end of the ear. Pass the ear of corn around the room for students to observe and take notes of like they did of the ovule last class period.
  4. Explain the route that pollen must make for the pollination and fertilization to occur.
    1. Ask the students why it would be important for corn to get fertilized.
    2. Talk about factors that could affect the success for failure of pollination.
      1. Some factors could be growth of the tassels, growth of the silks, distance between the two, amount of wind, nutrition of the plant, plant pests, etc.
  5. Tell students to look in their science notebooks. Look at the similarities and differences between the flower yesterday and today’s corn plant. Have them compare and contrast the two together as a class.
    1. Talk about which plant as perfect and imperfect flowers. Which has complete and incomplete. Why is that?
  6. Lead the discussion into detasseling, and why that is practiced.
    1. Introduce the idea of cross-breeding and selective breeding. Ask students why people might want to use these methods.
    2. Help students discover that not all corn is planted for consumption; some must be planted for seed the following years.
      1. Therefore, not all corn fields are detasselled; only the ones planted for seed.
      2. These fields will have “male” rows between every three or four female rows to pollinate them. This will be what creates the hybrid seeds.
  7. Wrap up with a short discussion, and have students finish filling out their study sheets.

Essential Files (maps, charts, pictures, or documents)     

Did You Know? (Ag Facts)

  • Iowa grows more corn than any other state – most field corn, not sweet corn.
  • Iowa also leads the nation in soybean production, egg production, and pork production.
  • Corn is used in a multitude of products, from packing peanuts to pop to carpet and plastics!

Extension Activities (how students can carry this beyond the classroom)

  • Have students collect five different types of flowers and determine if they are perfect or imperfect flowers.
  • Have students conduct research on common Iowa agricultural crops and how they are pollinated.

Sources/Credits

Author(s) (your name)

  • Scott Krosch

Organization Affiliation (your organization)

  • Sioux City Community Schools

National Agriculture Literacy Outcomes and Iowa Core Standards

  • Science, Technology, Engineering & Mathematics:
    • T4.6-8.b: Describe how biological processes influence and are leveraged in agricultural production and processing (e.g., photosynthesis, fermentation, cell division, heredity/genetics, nitrogen fixation)

Iowa Core Standards

  • Science:
    • MS-LS1-4 Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively.
    • MS-LS1-5 Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms.