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Name Date Period

ALTERNATION OF GENERATIONS

Alternation of generations is one of those plant biology buzzwords that we biology teachers like for students to know really well. The two "parts" of the generation are the sporophyte and gametophyte, which differ in their ploidy level (number of chromosomes) and in their morphologies as well (usually, but not always). Here is the pattern. It is pretty much the same for all plants, and it's worthwhile remembering (hint).

The sporophyte is diploid and the gametophyte is haploid. The diploid undergoes meiosis to produce haploid spores. The haploid spores germinate and grow into the gametophyte. The gametophyte produces gametes (sperm and egg) without meiosis-- it's haploid already! The egg and the sperm fuse to form a diploid zygote. The zygote develops into the sporophyte.

Moss Lifecycle Fern Lifecycle

Once you understand the sequence above, your job in this lab is to identify the different parts of the cycle on real organisms, including mosses, ferns, a conifer, and an angiosperm. The main objective of this laboratory is to expose students to some of the frequently encountered major Divisions within the Plant Kingdom, incorporating considerations of life cycle into the "general recognition" aspects of this little survey. Be advised that this survey of Plant Divisions is minimal, there are a lot of other plant divisions that we could be looking at-- all of them would conform to the pattern of alternation of generations.

STUDY HINT: the gametophyte generation always produces gametes

the sporophyte generation always produces spores

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Name Date Period

PLANT KINGDOM CLASSIFICATION

Nonvascular Plants: No water-conducting cells (xylem).

Division Bryophyta (mosses). Division Hepatophyta (liverworts). Division Anthocerophyta (hornworts).

Vascular plants: Xylem tissue, true roots, stems & leaves.

Spores but no seeds

Division Psilophyta (Psilotum or whisk fern). Division Lycophyta (club mosses). Division Sphenophyta (horsetails). Division Pterophyta (ferns).

Seed Plants

Gymnosperms--Naked Seeds

Division Cycadophyta (cycads). Division Ginkgophyta (Ginkgo or maidenhair tree). Division Gnetophyta (Ephedra & Welwitschia). Division Coniferophyta (conifers).

Angiosperms--Seeds Enclosed In A Fruit

Division Anthophyta (flowering plants)

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Station #1: Mosses

1. To what Division do mosses belong?____________________ 2. Why are they called nonvascular plants? 3. Is the dominant generation for the moss the gametophyte or sporophyte? 4. Sketch a plant from the moss sample and label the

following terms: gametophyte, sporophyte, sporangium, 2n part of plant, 1n part of plant, rhizoids

5. Are the spores produced by the moss sporophyte formed

from meiosis or mitosis? Are they haploid or diploid? 6. Are the gametes haploid or diploid? Are they produced from meiosis or mitosis?

Station #2 Liverworts

1. To what Division do Liverworts belong?___________________

2. Is the liverwort you observe a gametophyte or sporophyte?

3. Sketch the liverwort and label: thallus, gemma cup, rhizoids

4. Are the gemmae responsible for sexual or asexual

reproduction? Explain.

Station #3: Horsetails

1. To what Division do Horsetails belong?________________ 2. Why are they considered “seedless vascular plants?” 3. What is the strobilus?

Moss Sketch

Liverwort Sketch

Horsetail Sketch

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Station #4: Ferns

1. To what division do ferns belong?____________________ 2. Is the dominant generation for the fern the gametophyte or sporophyte? 3. Sketch the basic lifecycle of the fern. Include the terms: gametophyte, sporophyte, 2n, 1n,

sporangium, spores

Station #5: Gymnosperms (Cycads and Ginkgo)

1. Is the dominant generation for the vascular plants with seed the gametophyte or sporophyte? 2. What is a gymnosperm? 3. To what Division do the Cycads

belong?________________________ 4. To what division does the Ginkgo belong?______________________ 5. What is unique about the Ginkgo? 6. Sketch a Ginkgo leaf.

Cycad Sketch

Ginkgo Leaf Sketch

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Station #6: Gymnosperms (Welwitschia & Ephedra)

1. To what Division do these plants belong?_______________________ 2. In what environment would you expect to find an Ephedra plant? 3. What is the pharmaceutical significance of the plant?

Station #7: Gymnosperms (Conifers)

1. To what Division do pine trees belong?___________________ 2. Why are pine trees called “Conifers?” 3. Why do Conifers produce so much pollen? 4. Sketch a male vs. female cone from the sample branch.

Station #8: Angiosperms (Flowering Plants)

1. To what Division do all flowering plants belong?_____________________ 2. What is the adaptive advantage of flowers? 3. Sketch a brief, basic illustration of the flowering plant life cycle. (Don’t worry about what is

happening inside the seed!) 4. Is the dominant generation of flowering plants the

gametophyte or sporophyte?

5. Sketch and label a flower … include all terms on the information sheet

Male vs, Female Cone Sketch

Flower Sketch

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Station # 1: Nonvascular Plants Mosses, Liverworts and Hornworts Mosses (Division Bryophyta), liverworts (Hepatophyta) and hornworts (Anthocerophyta) all share the following common characteristics:

no vascular tissue (specialized conductive tissue for transporting food and water)

gametophyte stage is dominant

In mosses, most of what you see is gametophyte. Mature gametophytes have antheridia for producing sperm and archegonia where eggs are kept. Water--either submersing the plant or covering it in a film-- is crucial for allowing the sperm to swim/splash on over to the archegonia, enter and fertilize the egg cell residing deep within the archegonium. The sporophyte develops from the zygote and grows almost like a parasite or a tumor, sucking resources away from the gametophyte. Usually, there's not much to the sporophyte. In most common mosses, it's a long skinny filament with a capsule at the end, where meiosis takes place, spores form and from which the spores are released. The spores germinate into a filamentous haploid structure.

MOSS SPECIMEN ACTIVITY Try to find gametophytes, sporophytes on the moss samples available. On the gametophyte, note rhizoids (root-like structures) and leaf-like structures. Try to find archegonia and antheridia. On the sporophyte, note the foot, seta and capsule (called a sporangium). If you're thinking now, "Whoa, this moss taxonomy thing is really for me," then allow me to appease further your whetted interest. The calyptra is like a little "hat" that the capsule wears. It pops off the top of the archegonium when the sporophyte starts growing. If you remove the calyptra from the capsule, you'll see (actually you'll need the stereoscope to see this) a row of teeth--the peristome--on the capsule under the hat. The peristome is one of the "more important" characters used by taxonomists for classifying mosses. Open the capsule and see if you can find any spores. Mosses are often the first plants to colonize a newly available habitat. In a moist environment, spores will germinate and grow into a branched multicellular structure called a protonema. The cells of the protonema contain chlorophyll and also give rise to the rhizoids (lacking chlorophyll), which penetrate the soil. Buds on the protonema develop into the leafy shoots of the mature gametophyte.

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STATION #2: LIVERWORT SPECIMEN ACTIVITY Examine the liverwort specimen (Division Hepatophyta). Liverworts have a flattened body (thallus) with tiny palmlike stalks bearing male and female sex organs (the sample we have probably does not have the sexual reproductive structures right now); the gametophyte thallus of some species also bears small, cuplike structures called gemmae cups. The cups contain lens-shaped buds called gemmae, which can grow asexually into new thallus plants when they are washed out by rain.

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Station #3: Seedless Vascular Plants Division Sphenophyta: Horsetails Primitive vascular plant group of the Carboniferous Period (300 million years ago) with jointed stems, whorls of tiny scale-like leaves at the nodes, and a terminal spore cone (strobilus); some species with dense branches at nodes, apparently resembling a bushy horse's tail to some botanists. Also called "scouring rushes" because the silica-impregnated stems were used to clean pots and pans. Many fossils, including tree-like forms dating back 300 million years ago; the present-day genus Equisetum is a living fossil with several species that are the only living representatives of this ancient group of vascular plants.

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Station #4: Seedless Vascular Plants

Division Pterophyta: Ferns Ferns have the following character states:

dominant sporophyte generation

independent gametophyte generation

Gametophytes that develop from spores generally have the ability to form both antheridia and archegonia, and thus can produce both kinds of gametes. Some ferns produce two types of spores that develop into unisexual gametophytes which possess either archegonia or antheridia. Once released from the mature sporophyte, a spore that finds appropriate conditions will absorb water and germinate in the soil. The spore develops into a small, heart-shaped, photosynthetically active gametophyte. Rhizoids develop early and help anchor the gametophyte to the soil. Antheridia and archegonia develop on the lower surface. When water is present below the gametophyte, the sperm are released and swim using their flagella toward an archegonium. Sperm move into the neck of an archegonium and fertilize the single egg located at the base of the archegonium. The resulting zygote begins immediately to develop into a sporophyte while still attached to the gametophyte. The young sporophyte uses resources from the gametophyte, and the embryo quickly develops its leaves and roots and begins an independent life. In most cases, only a single sporophyte can develop from a mature gametophyte.

FERN SPECIMEN ACTIVITY Examine the fronds (“leaves”) of a mature sporophytic stage of the fern specimen. Identify the rhizome (underground stem w/ roots) and young leaf (fiddlehead). Find fronds that bear spores and note the location and arrangement of the sacs called sori (singular sorus), which are composed of clusters of sporangia that contain spores. Scrape a small portion of a sorus onto a slide and examine the sporangia under the compound microscope. Spore discharge in ferns is an interesting event. If you have time, put a part of a frond (with mature sporangia) under the dissecting microscope with a hot light on it, in order to view spore discharge.

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Vascular Plants with Seeds…General Info

Seed plants have the following character states:

dominant sporophyte generation

highly reduced gametophyte generation in which the female gametophyte remains part of the seed parent

sperm carried from pollen parent to seed parent as part of the pollen grain

nonflagellated sperm travels to female gametophyte via a pollen tube

Station #5: Vascular Plants with Seeds

Gymnosperms (naked seeds) Division Cycadophyta: The Cycads

Palm-like plants with large seed and pollen cones. Flourished during the days of the dinosaurs and undoubtedly were a major food supply for herbivorous dinosaurs; cycads were so numerous in Mesozoic times that this era is often called the Age of Cycads and Dinosaurs. Cycads are dioecious species with pollen cones and seed cones produced on separate male and female individuals (as opposed to male and female parts being on the same plant). In some species, the enormous pollen and seed cones may reach 3 feet in length and may weigh up to 90 pounds. (Commonly called Sago Palm in the nursery trade, they are not actually palm trees.)

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Station #5: Vascular Plants with Seeds

Gymnosperms (naked seeds) Division Ginkgophyta: Ginkgo

Seeds borne in pairs on dwarf shoots. The unique, fan-shaped leaves and naked seeds of living Ginkgo biloba trees have changed very little in 200 million years. Although the naked, stalked seed resembles a cherry, IT IS NOT A FRUIT! A true living fossil; only one living representative of the entire Division: Ginkgo biloba.

Note: Most people only plant male Ginkgo trees because the "fruit" of the female tree stinks and is quite messy when it drops to the ground. Run out and take a look at the Ginkgo tree that is to the right of the entrance to the library (top left photo). Come right back to class!

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Station #6: Vascular Plants with Seeds

Gymnosperms (naked seeds) Division Gnetophyta: Welwitschia & Ephedra

Welwitschia mirabilis in the Namib Desert of southwestern Africa. The two strap-shaped leaves have been shredded after many decades of thrashing in the desert wind. Welwitschias also absorb moisture in the form of dense fog that flows over the Namib Desert. Although the desert receives little or no rain, the fog drip is apparently sufficient to sustain these remarkable plants that grow nowhere else on earth.

The Chinese species Ephedra sinica was the original source of the alkaloid ephedrine, a common decongestant in popular allergy and hay fever remedies. Since ephedrine has a chemical structure similar to epinephrine (adrenalin), it works like a powerful cardiac stimulant that may cause cardiac arrest in infants and heart patients. New synthetic drugs based on the ephedrine/epinephrine ring structure are now marketed as effective and safer bronchodilators. It is used in over-the-counter drugs such as Sudafed©. E. sinica and other species are also marketed under the name of "ma-huang," a popular herbal stimulant and decongestant.

Ephedra are drought-resistant shrubs with jointed stems and whorls of minute scale-like leaves.

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Station #7: Vascular Plants with Seeds

Gymnosperms (naked seeds) Division Coniferophyta: Conifers

Division Coniferophyta comprises the conifers, the most abundant gymnosperms today. Conifers are trees or shrubs that bear their seeds in cones (ex- pine trees), without the protection of a fruit as the angiosperms have. The cones contain all of the plant's reproductive structures. Like most plants, conifers have a life cycle following an alternation of generations pattern. The diploid generation, the sporophyte, is the plant itself, while the haploid generations, or gametophytes, are microscopic stages inside the cones. There are two types of cones on a conifer: the large, female cones that contain many ovules, which will produce the female gametophytes, and the much smaller, male cones, which produce the male gametophyte pollen grains. The male cones first produce spores by meiosis, which develop into pollen grains and rest on the edges of the cone. These are carried by the wind, and some will reach the female cones in pollination. The pollen grains then directly enter the diploid sporangium in the ovule, and a female spore is produced by meiotic division inside the sporangium; this spore becomes the female gametophyte. In several months, this will produce eggs, as the male spores produce sperm. A small tube grows from the male spore to the egg and releases the sperm, which fertilize the egg. After fertilization, which usually occurs over a year after pollination, the diploid zygote develops into an embryo, and the ovule grows a tough seed coat and becomes a seed. This will fall to the ground and germinate, eventually growing into another tree. This method of reproduction enabled the conifers to dominate the earth during the Mesozoic Era. In the Cretaceous Period, however, a new line of plants emerged: the angiosperms. These have flowers onto which the pollen lands during pollination, after fertilization, the ovule grows into a fruit. These came to dominate temperate climates; however, conifers still dominate the northern climates of the world.

CONIFER SPECIMEN ACTIVITY Observe the examples of conifers and their cones. Examine male and female pine cones in lab and relate the life cycle of a pine tree to these structures. Observe the female cone bracts and see if there are any seeds attached. If not, you will still be able to find a slight depression on the upper surface of the bract where the seen formed. Pollen grains form in the delicate little sacs under the male cone bracts. Because gymnosperms do not make flowers, and consequently do not attract pollinators, they rely on the wind alone for pollen transfer to female cones. Therefore gymnosperms make an amazing amount of pollen, with the hope that by chance some will get to female cones. This is why if you live near a pine tree you’ll find lots of yellowish pollen grains on your car windows or other local surfaces in the springtime.

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LIFE CYCLE OF A CONIFER

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Station #8: Vascular Plants with Seeds

Angiosperms (seeds enclosed within a fruit) Division Anthophyta: Flowering Plants

Division Anthophyta, the angiosperms, or flowering plants, contains 99.5% of all extant plant species, as well as 80% of all living plants. First appearing in the Cretaceous period, angiosperms contain several key adaptations that allowed them to become dominant in the plant world.

First of all, angiosperms typically have broad, flat leaves, which allows for a more efficient collection of solar energy and a better rate of photosynthesis. Also, the vascular tissues of angiosperms have much stronger cell walls than those of gymnosperms. The one most distinguishing feature of flowering plants, however, and the one that most accounts for their evolutionary success, is the flower.

In the life cycle of an angiosperm, the anther produces haploid spores, which develop into pollen grains, the male gametophytes. In the ovules, haploid spores develop into the female gametophytes, which produce eggs. During pollination, discussed below, a pollen grain lands on the stigma (unlike in gymnosperms, in which the pollen lands directly in the ovule), and grows a pollen tube down the stem of the carpel and into an ovule, through which sperm are released from the pollen grain. The sperm fertilize the egg in the ovule, creating a diploid zygote.

After fertilization, each ovule grows into a seed with a hard coat, containing a developing embryo and a food supply. The ovary grows fleshy tissue and becomes a fruit, which aids in seed dispersal. After germination, each seed can grow into a new plant.

The methods of pollen dispersal in angiosperms are adaptations that allow them to reproduce more efficiently. In gymnosperms, pollen is dispersed by the wind, which is a very ineffective method, wasting most of the pollen grains. In many angiosperms, the color or scent of the flower itself attracts specific animals to it, and to the nectar, a sugary fluid produced by angiosperms for just this purpose, inside.

While consuming nectar, animals, usually insects, birds, or bats, are dusted with pollen grains. The pollen usually is dropped off in another flower the next time the animal stops for a meal. Thus, many flowering plants have evolved relationships with very specific animals, to ensure that their pollen is distributed only to other plants of the same kind.

Two other reproductive adaptations enhanced the success of the angiosperms. The first is the rapid rate of seed production; unlike in gymnosperms, which often have periods of over a year between pollination and fertilization, most angiosperms cut that period to a few weeks. This enables them to take advantage of short growing seasons in many inhospitable habitats, such as deserts.

The other big advantage of the angiosperms is in seed dispersal. The evolution of the fruit allowed angiosperms to cultivate more relationships with animals: many animals like to eat the fruits, but the hard seed coats pass through animal digestive tracts and exit the animal, with some ready-made fertilizer, a good distance from the original plant. Thus, angiosperms have a very effective method of distributing seed that allow populations of the plants to quickly spread.

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Anatomy and function of the angiosperm flower. Not all features are found in all flowers, as there has been considerable evolution and modification of this basic pattern.

Sepals. These are the outermost tissues of the flower; they are what you see of a flower when in the bud stage, before it opens. Usually the sepals are green in color and photosynthetic.

Petals. These are the usually colored tissues that make flowers attractive to us and other animals. The petals may be equipped with nectar glands near their base, an attraction and reward for pollinators.

Stamen. The stamens can be regarded as the male part of the flower. A stamen consists of 2 parts: filament and anther. The anther is where pollen is made. Pollen grains are really tiny male gametophytes in the life cycle of angiosperms. Pollen grains therefore are important because they are the source of sperm in the angiosperm life cycle.

Carpel. The carpel is the female part of a flower (not all flowers have male and female parts, but most do). A carpel consists of three parts: stigma, style and ovary. The stigma is a sticky surface where pollen grains land and attach. The pollen grain bursts open and sends a sperm cell down through the style into the ovary. Within the ovary are the eggs = ovules. When fertilized, an egg becomes the seed. The ovary walls, which surround the eggs/seeds becomes the fruit of the flower.