The Importance of Seeds

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Objective

Students will describe the process of fertilization and seed formation in flowering plants.

Big Idea

Find out today how the development of enclosed seeds made angiosperms more successful than gymnosperms.

What Students Will Learn in this Lesson

1 minutes

Yesterday students learned about the role flowers placed in the successful spread of angiosperms. Today students will dissect several types of seeds to increase their understanding of monocots and dicots. After students determine the major distinctions between angiosperm seeds, they turn their attention to gymnosperms. Students test their power of predictions by comparing their results with the conclusions of scientists. Finally, students consider the criteria that make a seed successful. Here is an overview of what they will learn today.

Hook/Check for Understanding

3 minutes

At the lab tables, place several seeds and pictures of the flowers from which they came.  Ask students to predict which seeds they came from which flowers. Students should record their predictions in their lab notebooks.

(Note:  For this activity, several seeds from monocots and dicots are needed.  I use seeds from as many of the flowers from yesterday's dissection as I can.  I collect seeds throughout the years from the wild for use with this lesson.)

See attached images for use with this activity in lieu of live specimens.

 

Station 1: Corn Kernel (Monocot) Dissection

10 minutes

For this station students will compare monocot and dicot structure by dissecting corn kernels.  The following equipment will be needed for this dissection:

Per class

  • One bag of frozen corn (thawed) or seed corn (steeped overnight)

Per lab group

  • dissecting tray
  • dissecting pins
  • scalpel
  • probe
  • scissors
  • forceps
  • tare scale (with 0.01 g accuracy)

All sketches and responses should be completed in their lab notebook or students could use the attached handout. 

Place a kernel of corn on the dissecting tray.  Make a color sketch of the exterior.  Label the different areas on the kernel:  tip cap, pericarp (hull), germ, floury endosperm (white-colored), and horny endosperm (yellow-colored).  Remove the tip cap of the kernel.  Sketch it in the lab notebook.  Next remove the two layers of hull known as the pericarp.  Sketch it in the lab notebook.  Finally, separate the remaining portion (the endosperm) of the kernel into the floury endosperm (white part) and the horny endosperm (yellow part).  Make a sketch of each in the lab notebook.  Estimate, using percentages, the approximate part of the total kernel that each kernel component represents.  Verify group estimates by weighing corn components on the tare scale.  (Note: If a 0.01 g accuracy scale is not available, multiple groups can weigh their kernel components together and the total weight can be divided by the total number of individual components.) 

Have students construct a chart in their lab notebooks comparing the actual (accepted) weights/established amount (%) for each part of the kernel. Dispose of corn kernel pieces.

Next, have student place another kernel of corn on the dissecting tray.  Have student bisect the corn kernel lengthwise.  Make a color sketch of the interior.  Label the different areas on the kernel:  tip cap, pericarp (hull), germ, floury endosperm (white-colored)and horny endosperm (yellow-colored). Dispose of corn kernel pieces. 

based on Corn Kernel Dissection Lab from www.biotech.iastate.edu

Station 2: Lima Bean (Dicot) Dissection

10 minutes

For this station students will compare monocot and dicot structure by dissecting lima beans.  The following equipment will be needed for this dissection:

Per class

  • One bag of frozen lima beans (thawed) or seed lima beans (soaked overnight)

Per lab group

  • dissecting tray
  • dissecting pins
  • scalpel
  • probe
  • scissors
  • forceps
  • tare scale (with 0.01 g accuracy)

All sketches and responses should be completed in their lab notebook or students could use the attached handout. 

Place a lima bean on the dissecting tray.  Make a color sketch of the exterior.  Label the different parts of the bean: hilum, seed coat, plumule, epicotyl, hypocotyls, radicle, and cotyledon. Place a lima bean on the dissecting tray.  Remove the seed coat and sketch it in the lab notebook.  Next remove the hilum.  Sketch it in the lab notebook.  Finally, separate the cotyledon from the epicotyl, hypocotyls, and radicle.  Make a sketch of each in the lab notebook.  Estimate, using percentages, the approximate part of the total seed that each bean component represents. Verify group estimates by weighing bean components on the tare scale. (Note: If a 0.01 g accuracy scale is not available, multiple groups can weigh their bean components together and the total weight can be divided by the total number of individual components.) 

Have students construct a chart in their lab notebooks comparing the actual (accepted) weights/established amount (%) for each part of the bean. Dispose of bean pieces.

Next, have student place another bean on the dissecting tray.  Have student bisect the bean lengthwise.  Gently remove the seed coat from the exterior of the bean.  The bean will naturally separate into two equal portions.  Make a color sketch of the interior.  Label the different part of the bean: hilum, seed coat, plumule, epicotyl, hypocotyls, radicle, and cotyledon. Dispose of bean pieces. 

Station 3: Testing your power of prediction

10 minutes

In this station, students will compare the seeds they viewed at the beginning of the period and determine if they are monocot or dicot.  They will also find out from what flower they came. (See attached images: conefloweryellow evening primrosebig bluestemAmerican sycamore, and wild plains indigo.)

First, students should make a list of similarities and differences between dicots and monocots much like the list made in yesterday's lesson. They may add the existing list if they want. 

Using the student generated list, each student group should view the seed samples on by one and determine if the sample is a monocot or dicot.  Students should list reason why they made the choice they did. 

Station 4: Pine Seed (Gymnosperm) Dissection

10 minutes

For this station students will compare gymnosperm seed structure to angiosperm seed structure by dissecting pine seeds.  The following equipment will be needed for this dissection:

Per class

  • Several pine cones that have been soaked overnight for easy removal of seeds

Per lab group

  • dissecting tray
  • dissecting pings
  • scalpel
  • probe
  • scissors
  • forceps
  • tare scale (with 0.01 g accuracy)

All sketches and responses should be completed in their lab notebook or students could use the attached handout. 

Peel back the scales of the pine cones and remove two seeds from the cone.  Place one of the seeds on the dissecting tray.  Make a color sketch of the exterior.  Label the different parts of the bean: seed coat, megagametophyte, and cotyledon. Place a pine seed on the dissecting tray.  Remove the seed coat and sketch it in the lab notebook. Next, separate the megagametopyhte from the cotyledon.  Make a sketch of each. Estimate, using percentages, the approximate part of the total pine seed that each seed component represents.  Verify group estimates by weighing seed components on the tare scale. (Note: If a 0.01 g accuracy scale is not available, multiple groups can weigh their kernel components together and the total weight can be divided by the total number of individual components.) 

Have students construct a chart in their lab notebooks comparing the actual (accepted) weights/established amount (%) for each part of the pine seed. Dispose of pine seed pieces.

Next, have student place another pine seed on the dissecting tray.  Bisect the pine seed lengthwise.  Gently remove the seed coat from the exterior of the pine seed.  The pine seed will naturally separate into two equal portions.  Make a color sketch of the interior.  Label the different part of the pine seed: seed coat, megagametophyte, and cotyledon. Dispose of pine seed pieces. 

Putting It All Together: What Makes a Seed Successful

15 minutes

Students should compare and contrast the three seeds they dissected today.  In particular, students should look at adaptations made by angiosperms. 

Using images from prepared slides, explain the adaptations that have made angiosperms more successful than gymnosperms.  (Note: See attached powerpoint, Comparing Seeds.)

Then present students with the Seedlings in a Jar Assessment Probe. Ask students to compare the mass of a closed system (jar) before and after seed germination. Use this probe to elicit student ideas about germination and plant growth as well as conservation of matter in a closed system.

Students should write their responses to the following questions in their lab notebooks.

(Note: I place parsley seeds in moist peat pellets while I am explaining the probe to the class.  Then I place a bell jar on the top of the pellets and seal the bell jar with clear packing tape. Then I show the students the image on the assessment probe handout.  I use the Seedlings in a Jar assessment probe powerpoint and have students write their responses in their lab notebook.  I have included a handout to use in lieu of lab notebooks.)