to observe the parts of the flower and the related functions of those parts
The Plant Kingdom is composed of organisms that are extremely small to some of the largest on the planet. Plants share the same basic mechanisms of photosynthesis, have cell walls composed of at least 35% cellulose, possess chlorophylls a and b, and frequently store their photosynthate as starch. Alternation of generations describes the life cycle with sporophyte and gametophyte plants present at some point in the life of the plant. Gametes are formed in antheridia or archegonia borne on one or separate plants.
Plants are often characterized by the presence or absence of various structures. The first basic division of plants is on the basis of vascular tissue. Nonvascular plants tend to be very small because they lack vascular tissue. Moving water, nutrients and photosynthate through the plant is accomplished by short distance processes of diffusion, osmosis and facilitated diffusion. The BRYOPHYTA are the plant group that is nonvascular.
Bryophytes are traditionally divided into:
- true mosses
In the absence of microscope and slides, you will observe the plants and their parts by visiting the websites available through the embedded links.
We will examine some representatives from the mosses and liverworts. The typical leafy moss body frequently seen in moist woodlands is the gametophyte. Another picture of the leafy gametophyte. As the following site will show, mosses are found around the world. They contain structures that serve the function of the stem, the leaves and rhizoids to serve rootlike functions. See also A Photographic Atlas for the Biology Laboratory, 4th Edition, p.64
pictures of rhizoids; picture of stemlike and leaflike structures
The sporophyte emerges from the gametophyte, is nourished by it and is completely dependent upon the gametophyte. Visit this site to see the structure of the sporophyte. The sporophyte capsule may be simple or ornate but house the spores. Note the various parts. Another capsule picture. See also A Photographic Atlas for the Biology Laboratory, 4th Edition, p.64
Visit the following site and study the life cyle of the moss. The ON-Line Study Guide for the textbook, in the Concept Challenge Section of Chapter 21, has pictures of the life cycles to be labelled. See also A Photographic Atlas for the Biology Laboratory, 4th Edition, p.63
Liverworts derive their name from the mistaken notion that their leafy gametophytes resemble the lobes of the liver and thus might be useful in curing liver ailments. They may contain small, cuplike structures called gemmae cups which are involved in asexual reproduction. See also A Photographic Atlas for the Biology Laboratory, 4th Edition, p.58-59,62
picture of liverwort in its habitat showing male and female plants
picture of the liverwort Marchantia with gemmae cups
Seedless Vascular Plants - the Lower Tracheophytes
Ferns and Fern Allies
The Bryophytes represent an evolutionary dead end and never achieved any great size since they lack a vascular system. A number of plant groups began the development of a vascular system yet were still dependent upon water to get their gametes together. These plants, known as tracheophytes, show many of the structural adaptations that were necessary for an independent life on land, yet most of these plant groups lacked the necessary combination of features to serve as the ancestoral form of the higher plants.
This group of plants includes the ferns and their allies the whisk fern, Psilotum, the club mosses, Lycopodium and the horsetails, Equisetum. See also A Photographic Atlas for the Biology Laboratory, 4th Edition, p.65,66,69
Note the life cycle of the fern at your on-line study guide noted above and at this site. The familiar leafy structure seen in shaded areas is the sporophyte. There is an underground stem known as a rhizome from which rhizoids develop and serve a rootlike function. Note the labelled drawing.
On the underside of the leafy fronds you may see a darkish colored series of round to oval structures. These are the sori and represents a cluster of sporangia. The sori structure varies from species to species. The sori covering is called the indusium and protects the developing spores until they are matured. Mature spores are produced by meiosis and dispersed primarily by wind or contact with animals.
Spores that land in a suitable environment germinated into a heart-shpaed structure known as the prothallus. Both antheridia and archegonia are found in specific regions of the prothallus. When fertilization of gametes occurs the newly formed zygote develops into an independent sporophyte. The prothallus disintegrates.
See also A Photographic Atlas for the Biology Laboratory, 4th Edition, p.71-73
Two major evolutionary advances made possible the developement of the higher tracheophytes. First was the development of the seed from the ovule. The seed, contained in protected form, the embryo, a certain amount of stored food and a seed coat that often required special action for it to break open. This protected structure was analogous structurally to the egg of birds and some other animal groups. See also A Photographic Atlas for the Biology Laboratory, 4th Edition, p.97. The second advancement was development of the pollen grain. This protected structure represents the immature male gametophyte and provides plants with a means of becoming independent of water as a means of bringing gametes together. The higher tracheophytes are divided into the Gymnosperms, which do not produce flowers and the Angiosperms, which do.
Gymnosperms are divided into four divisions: the Conifers, the Cycads, Ginkgo, and the Gnetales. Pictures of the first three divisions can be seen in A Photographic Atlas for the Biology Laboratory, 4th Edition, p.74-77 The Conifers are the most numerous and best known of the groups. The cone represents the reproductive organs of the plant. Note the male and female cones on this branch. The seed of the pine is shown here. They include the pines, spruces, firs, junipers and many others. The Life Cycle of the Pine is the most commonly used example and is shown on page 76 of the PhotoAtlas. Go to this site for an interactive Pine Life Cycle.
pictures of one of the oddest members of the Gnetales
other members of the group are also shown on the same page
Comparing Angiosperms and Gymnosperms
The final group of vascular seed-producing plants also produces flowers. Check at this site for general characteristics of flowering plants. Flowers and cones represent highly modified spore-bearing leaves. Flowers and cones have carried the production and protection of male and female gametophytes to a series of amazing structural extremes. The female portion of the flower contains a swollen base called the ovary which houses the ovules. It is within this ovarian space that embryonic development begins with a double fertilization process. The seed(s) develop within the ovary and the ovary often adds additional tissue and becomes the fruit.
Be able to identify the various parts of the flower and the associated function of each part. There are four major parts that are normally identified. Use this site for a labelled picture of the flower.
- SEPALS - the outermost portion of the flower which protects and encloses the other floral parts in their bud stage of development; their color varies but is most frequently green
- PETALS - inside of the sepals, the petals are usually brightly colored or have some other means of attracting pollinators
- STAMENS - the male portion of the flower located inside of the petals; consists of a stalk called the filament and a terminal pollen forming structure called the anther
- PISTIL - female portion of the flower; an enlarged basal area called the ovary from which extends a slender cylinder called the style; at the top of the style is the sticky platform for pollen called the stigma
Another site for flower structure.
The Life Cycle of the Angiosperms is shown in A Photographic Atlas for the Biology Laboratory, 4th Edition, p.82; flower parts on shown on pages 92-96.
Angiosperms are further subdivided into Monocots and Dicots. There are a number of characteristics, including seed type, that determine which category an angiosperm will be in. Also see A Photographic Atlas for the Biology Laboratory, 4th Edition, p.83 for differences between monocots and dicots.
1. In each of the groups mentioned in this investigation, identify some of the adaptations present in each group that would have been necessary and helpful to make the transition from an aquatic lifestyle to a terrestrial one.
2. Be sure you understand the generalized life cycle of plants including the sporophyte generation and the gametophyte generation.
3. What is the difference between a perfect flower and an imperfect flower? What about a complete flower versus an incomplete flower. Relate some of these terms to the idea of monoecious versus dioecious plants.
4. What is (are) the purpose(s) of a flower?
The Plant Kingdom courtesy of Ohio State
Pictures of the various groups included in the Plant Kingdom
Tour at the University of Georgia
Word Lists and Pictures of all the Plant Groups