Week 7: Seed Plants

I. Alternation of Generations

As you learned in the last lab, plants undergo alternation of generations (Figure 1), which involves a haploid and diploid part of the life cycle. “Higher plants” such as gymnosperms and angiosperms spend less time near water and the majority of their life cycle involves macroscopic diploid (sporophyte) structures. The reproductive structures in both taxa are generally microscopic.

Key Terms

Activity 1: Classification of Gymnosperms and Angiosperms

Before lab, view and take notes on the following video.

Transitions or major evolutionary events (Figure 2 and Table 1) in the plant kingdom have been in part responsible for the success of the plant kingdom and eventually resulted in the evolution of “higher plants.” The first major evolutionary event in the plant kingdom is the development of a vascular system, the xylem and the phloem. Xylem transports water and minerals, while phloem transports carbohydrates. The first transition separates the non-vascular plants from the vascular plants. The second transition is the evolution of the seed and separates the seedless vascular plants from the seed (and therefore by definition vascular) plants (Figure 2 and Table 1).

Recent estimates of the total number of plant species place the numbers at >374,000 (Christenhusz and Byng, 2016) to > 450,000 (Prim and Jopp, 2015) species (see Table 1). As you can see in the table, the seed plants are by far the largest and most diverse group of plants.

Answer the following questions.

1. What do the numbers in the table imply about the evolutionary advantages of vascular tissue and seeds?

2. Why do you think each of these traits led to adaptive radiations? Answer this question in your lab report, or discuss it with the class.

3. What are the five characteristics of seed plants? The first is easy. They have seeds. Use your notes from the video above to find the answers.

a. Seeds
b.
c.
d.
e.

II. Gymnosperms

Before coming to the lab, review “Reading: Seed Plants” and your textbook to learn more about seed plants that are gymnosperms. Also familiarize yourself with the life cycle of a gymnosperm in the first six slides of “Seed Plants Lab.”

Activity 2: Life Cycle and Reproduction of Seedless Vascular Plants – Gymnosperm

Pre-lab: Life cycle

Record your answers to the following. The definitions are provided in the readings linked above.

1. Define microspore.

2. Define megaspore.

Take a look at the life cycle of a gymnosperm below.

3. What do the following pictures (A and B) represent (hint: sexual reproductive structures in gymnosperms)? Record your answers to the following in the report.

In the lab: Reproduction

Proceed to the demonstration table to obtain the prepared slides of the gymnosperm listed below. Please perform microscopy observations, and write your observations in your lab notebook.

Seed Vascular plants: Gymnosperms

• Phylum Coniferophyta
  • Specimen observations:
    • Male and Female Cone
    • Slides
      • Coniferophyta female strobilus w/megaspore mother cell
      • Pine seed (Pinus)

Gymnosperms are usually wind-pollinated. Based on the pine pollen slides available in the lab (or the micrograph below), answer these questions in your lab report.

1. Can you see the pollen grain from the pine? What does it resemble? (describe the shape)

2. What are the germinated structures (arrow) in Figure 4b called?

Observe a prepared slide of the pine ovule using high-power magnification. Cover the labels, and try to identify all of the structures labeled below.

Answer the following questions. Your instructor may require you to include the answers in your lab notebook or lab report. (The questions are from the source attributed below.)

1. Gymnosperms

a. Name the four subgroups within gymnosperms.

b. We will focus on conifers. Observe the conifer leaf samples available in the lab.

i. How does the needle-like leaf benefit the conifer?

c. Reproduction in Pines: As indicated in the reading, draw a simple pine life cycle in the space below. Be sure to include the terms egg, embryo, fertilization, megaspore, microscope, gametophyte, sporophyte, meiosis, mitosis, and pollen. Use this website to get you started: http://www.exploringnature.org/db/detail.php?dbID=32&detID=1895

d. Observe the pine cones on display in the lab. Are pine cones haploid or diploid?

e. Are male or female pine cones larger? Why do you think this is so?

f. View the slide of the pollen pine cone (male cone or male strobilus) cross-section.

i. Can you find the microspores on the slide?

ii. Are microspores haploid or diploid?

iii. What process do microspores undergo to form pollen grains?

iv. Can you find pollen grains on the slide?

v. Use the space below to draw what you observed under the microscope.

g. View the slide of the seed pine cone (female cone or ovulate cone) cross-section.

i. Can you find the megaspores on the slide?

ii. Are megaspores haploid or diploid?

iii. What process do megaspores undergo to form the egg or ovule?

iv. Can you find the egg on the slide?

v. Is the tissue surrounding the egg haploid or diploid?

vi. Once the egg is fertilized what structure will form?

vii. Use the space below to draw what you observed under the microscope.

h. View the pine seeds on display (if available)

i. Are the seeds haploid or diploid?

ii. How will the seeds be dispersed through the environment?

iii. What cell division process will the seeds undergo to create a new pine tree?

In the lab: Observation of the Ginkophyta – Ginkgo

Proceed to the demonstration table to observe the Ginkgo biloba samples. Please write or draw your observations in your lab notebook. Then answer the following questions.

1. What traits make the ginkgo belong in the gymnosperm taxon?

2. What differs about the ginkgo compared to other gymnosperms, such as the conifers (pines) that you observed previously?

III. Angiosperms

Angiosperms (Anthophyta) are comprised of nearly 300,000 species. Two main angiosperm groups are the monocots and the eudicots (dicots). Table 2 summarizes their differences.

Before coming to the lab, review the section on angiosperms in “Reading: Seed Plants” and your textbook to learn more about angiosperms. Also familiarize yourself with the life cycle of an angiosperm in slide 7 to the end of “Seed Plants Lab.”

Activity 3: Angiosperm Life Cycle Overview (Pre-lab)

Record your answers to the following in your report.

1. What are the 3 F’s representing angiosperms? The definitions are provided in the videos and in your readings.

a.

b.

c.

Activity 4: Monocots vs. Eudicots

Among the angiosperms, some 74,273 species are classified as monocots, and some 210,008 species are classified as eudicots (Christenhusz and Byng, 2016). Table 2 summarizes how monocots and eudicots differ with respect to six characteristics.

Pre-lab: Classification of Angiosperm

1. In Figure 6, observe the different prepared slides of sections of monocot (left) and eudicot (right) leaves, stems, and roots (and look at the following micrographs). Do your findings match the content of Table 2?

2. Look at the structures in Figure 7.

Figure 7a: Leaves of species 1

Figure 7b: Flowers of species 2

Figure 7c: Dissection (x-section) of stem of species 3

Figure 7d: Pollen of species 4

Determine whether each unknown species is a monocot or a eudicot, and write the answers in your lab report.

In the lab: Monocot and Dicot survey

Using the information in Table 2, identify the live plants on display in the lab as either monocots or eudicots. If weather permits, your instructor may also take the class outside to identify plants on campus as monocots or eudicots. Be aware that some of the plants in the lab or outside will be neither monocots nor eudicots—instead, they will be gymnosperms or maybe even seedless plants.

1. What traits did you observe that allow you to classify each plant as a monocot or eudicot?

2. See how many different plants you can classify, and make sketches or a list of them in your lab notebook or lab report.

3. Your instructor may have you download a free app for identifying plant species, such as Seek by iNaturalist. With this app, all you have to do is open the app, click the camera icon, and point your phone at the plant. The app will suggest an identification. It works on animals too!

Activity 5: Flower Structure

Below is a schematic and a real photograph of a flower for a hermaphroditic species (which has complete flowers). Complete flowers will have 1. Sepals, 2. Petals, 3. Stamens (composed of a filament and an anther), and 4. Pistils (also known as carpels and composed of a stigma, a style, and an ovary that contains ovules).

Anatomy of a flower

Consult Figure 8 and answer the following questions in your lab report.

1. What do the anthers produce?

2. What will you find in the ovary?

3. Using your knowledge of flower structure from the videos and the previous figure, label the indicated flower parts in your lab report.

a.

b.

c.

d.

e.

f.

Your instructor may ask you to make sketches of angiosperm reproductive structures in your lab notebook or take pictures with your phone to add to your lab report. Don’t worry about your artistic skills—drawing or sketching is simply a way of making observations, and most scientists use this skill from time to time. Be patient and just draw what you observe. Then label it. Chances are your sketches will come out better than you expect!

If there are flowering plants available in your home or outdoors, select one to examine. It is not usually permitted to pick live flowers (e.g., from a garden, park, or nature preserve), though if a flower has fallen to the ground you may collect it for closer inspection. Identify the floral structures that you have learned (petals, sepals, ovary, stamens, carpel, etc—refer to Figure 9 above). If you like, make a sketch or take a picture of the flower and include it in your lab notebook or lab report. Label it using your knowledge of flower parts (refer to Figure 9 above). If no flowers are available, search for images of various flowers on the internet and identify as many structures as possible in the images.

Survey of a flower

Complete a table like the one below, using the flower model in the lab or Figure 9 to identify the structures listed in the column on the left. (The following activity is from the source attributed below.)

Activity 6: Angiosperm Life Cycle and Reproduction

Angiosperm reproduction begins when a pollen grain lands on a stigma. If the pollen belongs to the same species, it usually generates a pollen tube that grows down the transmitting tissue of the style (Tamari and Shore, 2001) and enters the ovule (within the ovary) through the micropyle. Double fertilization occurs resulting in a zygote and the formation of a triploid (3n) endosperm.

Pre-lab: Angiosperm life cycle

Your instructor might direct you to view this short video, “Life Cycle of an Angiosperm.”

As you know by now, fruits are the mature ovaries that surround and protect the seeds in flowering plants. This means that many familiar foods that we do not normally think of as fruits are, scientifically speaking, fruits. Some examples of fruits are given in “Reading: Seed Plants.” Choose one or more of the activities below to help you relate what we’ve studied about angiosperm life cycles to fruits and plants that are familiar to you.

• Obtain a familiar fruit (orange, apple, pear, watermelon, banana, grape, berries). Cut the fruit in the middle—meaning, a transverse cut across the “equator” rather than a sagittal cut from the stem to tip. Try to identify the seeds contained within. If no fruits are available, search for images of cut fruits on the internet.
• Obtain (or search for an image of) another fruit—this time, choose one that we don’t normally think of as a fruit (tomato, zucchini, squash, nuts, cucumber, peas in a pod). Make a transverse cut and identify the seeds (or search for images on the internet).
• Compare the flowers of a particular plant to the fruit that grows later—use the internet to help find images. Can you see the part of the flower from which the fruit grows? Can you propose an explanation as to how seedless fruits are produced?
• Find images of a fruit that is consumed often in your culture or ethnic cuisine. (Remember, any part of an angiosperm that contains the seeds is technically a fruit!) Identify the seeds, and then find images of the adult plant (including its flowers) from the species that produces the fruit. Describe and make a diagram of the life cycle of the angiosperm that produces these flowers and fruit, using what you have learned in this lab and relating it to your chosen species.
• Head outside (or look out the window) and select one plant to observe more closely. Using a free app such as Seek or iNaturalist, identify the plant and read more about it. Take some photos and upload your observations in iNaturalist. In your lab notebook, draw a sketch, and record the date, the scientific and common names of the plant, the location, the size, whether fruit or flowers are present, whether it is an angiosperm or a gymnosperm (or a seedless plant!) and how you can tell. Describe the life cycle of the plant, using what you have learned in this lab. Add any information you found about the plant’s significance in its ecosystem. What benefits or harms does it have in its interactions with other species, including (but not limited to) humans?

Your instructor may ask that you make sketches of the flowers and fruits, or take pictures with your phone and copy and paste the image(s) into your lab report.

In the lab: Angiosperm reproduction

Proceed to the demonstration table to obtain the prepared slides of the angiosperm listed below.

• Life cycle of a flowering plant
  • Slide of young lily anther
  • Slide of mature lily anther
  • Slide of lily pollen (regular and germinated)
• Zea mays (corn) slide

Please, perform microscopy observations and write your observations in your lab notebook. And then, answer the following questions in your lab report. (The questions are from the source attributed below.)

1. As indicated in the reading, draw a simple angiosperm life cycle. Be sure to include the terms egg, embryo, fertilization, megaspore, microscope, gametophyte, sporophyte, meiosis, mitosis, and pollen. Use the video, “Life Cycle of an Angiosperm” to get you started.

2. View the slide of the lily anther cross-section.

a. Can you locate the pollen grains?

b. Is the pollen haploid or diploid?

c. What cell type underwent mitosis to create the pollen?

d. Is the anther (tissue surrounding the pollen) haploid or diploid?

e. Draw what you observed under the microscope.

3. View the slide of the lily pollen grains.

a. How many cells are held within a single pollen grain?

b. Draw what you observed under the microscope.

4. View the slide of germinated pollen. Draw what you see. Your instructor may also have you prepare a wet mount of angiosperm pollen and treat it with a sugar solution to induce germination. Why do you think sugar induces the germination of pollen grains?

5. Although there is not a live corn seed available, please view the prepared slide of corn seed.

a. How many cotyledons does the corn seed have?

b. Is the corn a monocot or a eudicot?

c. What is the function of the endosperm tissue?

The Three Sisters

Now that you have learned a bit more about angiosperm growth and reproduction, let’s consider some interactions among different species of plants. You may have heard of the Native American Haudenosaunee legend of the Three Sisters. Three Sisters agriculture refers to the greater productivity achieved when corn, beans, and squash are grown together rather than separately.

You may also want to read the first three paragraphs of the article How to Grow a Three Sisters Garden and then watch this video.

With your lab group, brainstorm some questions or hypotheses that you could propose about the relationships between plants and humans, based on your unique perspective, culture, and experiences. Consider, for example, traditional foods or medicinal treatments from plants, or cultural ways of interacting with plant ecosystems (agriculture, recreation, spiritual practices, etc).

What kinds of questions or hypotheses arise in your mind when you reflect on these parts of your background?

What unique perspective or insight do you bring to the study of seed plants because of your culture, traditions, or experiences?

IV. Post-lab Questions

Answer the review questions below. (The questions are from the source attributed below.)

1. What does the gymnosperm mean?

2. What group of gymnosperm plants is the largest?

3. What type of spore is used for male reproduction in seed plants?

4. Through mitosis, the male spore develops into what structure?

5. What type of spore is used for female reproduction in seed plants?

6. Through mitosis, the female spore develops into what structure?

7. What does angiosperm mean?

8. What structures of the flower are female?

9. What structures of the flower are male?

10. What is the function of the petals of the flower?

11. The process of _____ occurs in the flower anther to create haploid _____ followed by mitosis to create _____.

12. The process of _____ occurs in the flower ovary to create the haploid _____ followed by mitosis to create the _____ and the n+n _____.

13. State one difference between monocots and eudicots.

14. Explain how angiosperms undergo double fertilization.

15. What part of the flower develops into a fruit?

16. If a plant had parallel leaf veins would you identify it as a monocot or a eudicot?

17. You look at a stem cross-section and notice there is a ring of vascular bundles. Would you identify it as monocot or eudicot?

18. Are fibrous roots more common in eudicots or monocots?

Attribution

Questions in this lab are adapted from “5.1: Seed Plants Lab” by Lynette Hauser, licensed CC BY 4.0.