There was a time when the land mass of the Earth was covered by mosses, ferns, and related plants. However, for the last 100-200 million years two great groups of plants have become dominant plant forms, the cone bearing plants (conifers) and the flowering plants. In this unit you will study these two groups, particularly their life cycles and the adaptions they have evolved that make them so successful.
Learning Objectives: The successful student will be able to ...
- describe the structure of a typical angiosperm and gymnosperm and name representative examples from each group.
- describe in detail the life cycle of these two groups and compare them to one another.
- identify and explain the function of the structures of a typical flower.
- list and explain the differences between monocot and dicot flowering plants.
- explain the role of physical factors such as wind and animals in the pollination of conifers and flowering plants.
Lesson One: Introduction to the Conifers and Flowering Plants.
Start by going to the University of California Museum of Paleontology Tree of Life project. Here you find a cladogram of the plant kingdom. The origin of the cladogram is in the center and branches out to the periphery. Notice that the "seed plant" are grouped together with other vascular plants such as the ferns (pteridopsida) and lycophypta. On the other hand, the non-vascuclar mosses (bryophyta) are more distantly placed from the seed plants. Read the material on this page and then follow the link to the "seed plants" and read the material there. You should be familiar with the taxonomic terms "gymnosperm" and "angiosperm." Even though these terms are a bit dated, they are still widely used. Finally go to the Horticulture & Crop Science resources of Ohio State University. Follow the links to the Gymnosperms and the diversity of Angiosperms. Read the material here with the goal to become familiar with the variety of plants in these two groups, there place in the evolutionary history of plants, and their unique reproductive structures.
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- What important anatomical feature to the angiosperms and gymnosperms share in common with the ferns? What habitats did this allow these plants to occupy that was unavailable to mosses?
- What important reproductive feature is unique to the angiosperms and gymnosperms? How did this feature allow these plants to invade habitats unavailable to ferns?
- What additional reproductive feature evolved in the angiosperms? What advantage did this give the angiosperms over the gymnosperms?
- List three structural/anatomical differences between monocots and dicots and give three specific examples of plants belonging to each group.
Lesson Two: Life Cycle of Conifers.
The "gymnosperms" include several groups of plants in addition to the conifers. Other gymnosperms (e.g. cycads and ginkos) were once common but are now represented by a very small number of species. Use the pages in Kimball and the Online Biology text to review the life cycle, general structure, and representative examples of the gymnosperms. Pay particular attention to the alternating generations of diploid sporophyte and haploid gametophyte and their relationship to the "tree" and "cones" we associate with a typical conifer. Pay attention to the relative size of the two "generations" and the typical method of pollination and the development of the seed.
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- What is a pollen grain in terms of the the life cycle of a conifer? Is it a sporophyte or gametophyte, diploid or haploid, male or female?
- What is a "seed" and why does it give conifers the ability to thrive in cold and dry environments?
- What is "pollination" and how does this occur in most gymnosperms?
Image of Cycad from Singh, GGSIPU, Delhi
Lesson Three: Life Cycle of Flowering Plants.
Of all the groups of plants, the angiosperms or flowering plants have the greatest diversity of species. As their name suggests, they all have the development of flowers as an important feature of their reproduction. Some angiosperms have flamboyant flowers (orchids and roses) and others the flowers are inconspicuous (grasses). However, the details of their life cycles are similar and you should be familiar with the specialized structures of a "typical" flower and the events in the life cycle of these plants. Read the pages in Kimball, the Online Biology text, and the OSU site. Pay attention to the same features of the alternating generations that you did with the gymnosperms. Be sure you can identify the various structures of a flow associated with the production of the egg, sperm, and fertilization. Understand what is meant by "double fertilization" and its relationship to the "endosperm" found in the seed. Appreciate the greater variety of pollination methods available to flower plants compared to the conifers.
Homework, Due . Email the answers to the following questions using your Fontbonne account.
- What is "endosperm" and how does this tissue come to be triploid?
- A common mistake is to call a pollen grain the equivalent of a sperm cell in animals. Explain why this is only partially true.
- Do some research and find out what the term "sexual mimicry" means. Describe at least three different examples of sexual mimicry that involve the pollination of plants.
- Do some more research and find out what crisis has befallen the honey bee in North America. Explain why this could have a serious impact on your food supply.
Fly Orchid from killerplants.org
