Pre-lab homework Lab 2: Reproduction in Protists, Fungi, Moss and Ferns

Transcription

1 Pre-lab homework Lab 2: Reproduction in Protists, Fungi, Moss and Ferns Lab Section: Name: 1. Last week in lab you looked at the reproductive cycle of the animals. This week s lab examines the cycles of the Fungi and starts looking at Plants. Using the lab from last week compare the animal life cycle from last week to the fungal and plant life cycles found in this week s lab. How are the cycles similar? How are they different? (hint: look at the introduction to exercise 1 and 3 in this week s lab!) 2. The reproductive cycle for plants is quite different from animals. One of the differences is the alternation of two distinct generations in the plants. Look over the lab (and in your text) and briefly describe the difference between the gametophyte and sporophyte generations in the plant life cycle. 3. What type of protista are we going to look at in lab this week? 1

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3 Lab 2: Reproduction in Protists, Fungi, Moss and Ferns Lab section Name: Objectives: Upon completion of this activity, you should be able to: Compare the life cycles of plants animals and fungi. Describe the reproductive structures of fungi. Identify the different generations of the plant life cycle. Describe reproduction in the algae Spirogyra and Volvox. Introduction: Sexual reproduction in the Fungal and Plant kingdoms is in many ways very similar to that seen in the animals. As with all sexual reproduction diploid cells must undergo meiosis to generate haploid cells and haploid cells fuse to regenerate cells with two copies of each chromosome. As you examine the details of the systems used by plants and fungi though you should pay attention to several differences from what happens in animals. First in both plants and fungi meiosis produces haploid spores not gametes as occurs in animals. These haploid spores germinate and undergo mitosis to build a haploid multi-cellular organism. In plants specialized structures develop on this haploid organism that produce gametes by mitosis. In fungus no specialized gametes are produced rather most of the cells in the fungus can join with cells from other individuals to generate a cell with two copies of each chromosome. Asexual reproduction is also a much more common strategy in both plants and fungus than it is in animals. Often times the same plants and fungi are able to do both sexual and asexual reproduction so that you will sometimes see the same organism reproducing both sexually and asexually. Exercise 1: Fungal reproduction: Reproduction in the fungal kingdom is different from animals in many ways yet as we will see there are some similarities as well. Asexual reproduction: Like many plants and some animals most fungi can reproduce both sexually and asexually. Asexual reproduction can help fungi to spread from one area to another more easily since a single spore landing in a favorable area can reproduce asexually to generate a large population of organisms without the need for a sexual partner. Asexual reproduction though has the problem of creating only identical offspring and this seems to be a large problem indeed. By using both modes of reproduction fungi may have the best of both worlds. 3

4 Asexual reproduction in fungi continued: Yeast is an example of a fungus that reproduces asexual. This process is called budding. In fact even though we suspect yeast can also reproduce sexually the sexual phase of the yeast lifecycle has never been observed. Examine a prepared slide of budding yeast and in the space below draw a picture of what you observe Budding Yeast Sexual reproduction in fungi: If cells from one individual encounter another individual of the same species but of a different mating type (fungi do not have sexes since they do not make gametes but to ensure they do not mate with themselves they have mating types usually designated (+) or (-)) they may fuse to create a dikaryotic cell one that has two nuclei! This is the first step in sexual reproduction in fungus. These cells then may undergo a large number of cell divisions before they ever fuse their nuclei and produce a truly diploid cell. Once this fusion has occurred these diploid cells may divide by mitosis for a while or, more commonly, undergo meiosis with little mitosis to produce haploid spores that can once again grow into a new organism. Mitosis Haploid or Diploid? Haploid or Diploid? Asexual reproductive structure Mitosis Mitosis Haploid spore Mitosis Haploid spore Complete the diagram to show sexual reproduction in fungi. The diagram above shows how a fungus can undergo asexual reproduction (the section on the left) but it needs to be filled out to include sexual reproduction. First circle the term that applies in the larger circle (haploid or diploid) then draw arrows to represent fertilization and meiosis. 4

5 Where is the diploid phase? As you can see in the above description the diploid phase of a fungus is short lived but the dikaryotic (two nuclei) phase can be quite large. In fact the gilled mushrooms that you buy at the store are actually dikaryotic reproductive structures. These mushrooms offer a good opportunity to examine the reproductive structures of fungi. Using prepared slides and live specimens examine gilled mushrooms and identify their reproductive structures. side view of a mushroom view under the cap showing gills Sketch a fresh mushroom in the space above, be sure to identify the gills and then examine the prepared slides of a gilled mushroom and locate the small stem, the gills and the spores. (hint: the cross section is like a very thin slice through the mushroom!) Cross section through gilled mushroom 10x Highly magnified gill showing spores 400x Try to identify the cells in the above diagrams that are haploid, diploid, and dikaryotic. (hint: they look the same you must use your knowledge of fungal reproduction to identify the cells!) 5

6 Exercise 2: Reproduction in the Kingdom Protista: Because there are such a wide variety of organisms that belong to the Kingdom Protista no single lifecycle can represent this group. Many members have the ability to asexually reproduce through mitosis. Many members, including most algae, also have the ability to undergo sexual reproduction. In most algae the dominate form is haploid. So when you are visiting the coast looking at algae in tide pools or see freshwater algae in streams those organisms are haploid. During sexual reproduction some algae produce specialized gametes through mitosis. Those cells merge to produce diploid cells which undergo meiosis to produce haploid cells that will grow into a new algae individual. Other algae don t produce specialized gametes but rather two haploid cells simply merge to form a diploid cell that will undergo meiosis to produce new haploid algae individuals. Asexual Reproduction in Volvox: Volvox is also a common green algae found in freshwater. The cells form colonies that are hollow spheres with fluid filled centers. Volvox undergoes asexual reproduction when individual cells from the colony drop into the fluid filled center and through mitosis form new daughter colonies. Eventually the parent colony will rupture releasing the new daughter colonies. Sexual reproduction can also occur, usually during stressful environmental conditions. At this time female Volvox colonies will produce eggs and male Volvox colonies will produce sperm, both through mitosis. The sperm are motile (can swim) and will fertilize the eggs. The resulting diploid zygote will undergo meiosis to create new haploid cells that through mitosis will form new colonies. Obtain a prepared slide of Volvox. Examine the slide under low power and look for daughter colonies. Draw a picture of Volvox in the box below. Volvox with daughter colonies 6

7 Sexual Reproduction in Spirogyra: Spirogyra is a common filamentous green algae found in freshwater. While there are not male and female individuals, there are filaments that are strains of Spirogyra that are called + and strains that are called -. In order for sexual reproduction to occur a + strain filament must come in contact with a strain filament. Sexual reproduction in Spirogyra is called conjugation. During conjugation the filaments grow a tube that will connect them. Through this tube the cytoplasm of the two filaments will merge forming a diploid zygospore. This zygospore will undergo meiosis to form new haploid Spirogyra filaments. Examine the prepared slide of Spirogyra conjugation and draw what you observe in the box below. Spirogyra conjugation 7

8 Exercise 3: Plant reproduction: Reproduction in the plant kingdom is different from both fungus and animals in many ways yet, as we will see, there are some similarities to both as well. So far you have seen that meiosis can give rise to either specialized gametes (as occurs in animals) or spores (as in the fungi). You also saw that diploid structures are created either by the fusion of specialized haploid cells called gametes (in the animals) or by the simple act of fusing nearby haploid hyphal cells (in the fungi). Reproduction in plants uses an interesting mix of these strategies. In plants meiosis produces haploid spores as in the fungi. These haploid spores divide through mitosis and grow into a haploid multicellular organism called the gametophyte generation. Unlike the fungi this haploid stage produces specialized reproductive gametes (sperm and egg) like animals do. These gametes then fuse and form a diploid zygote that undergoes mitosis and grows into a multicellular diploid stage called the sporophyte generation. This alternation of generations, from haploid gametophyte to diploid sporophyte is characteristic of all the plants but the different stages have very different sizes and shapes in different groups of plants. This week we will focus on the mosses, a group of plants that illustrate these differences dramatically, and the ferns, a group that illustrates the evolutionary trends of the plant kingdom. Next week we will continue investigating plant reproduction by examining the life cycle of the flowering plants. Figure 1. The generalized mitosis Haploid Gametophyte mitosis life cycle of plants meiosis spores (1n) gamete (1n) Diploid Sporophyte mitosis Fertilization Zygote (2n) gamete (1n) 8

9 Exercise 3a: Moss life cycles: In the moss the haploid gametophyte generation is an organism that is completely separate from the diploid organism. The gametophyte generation is the dominant stage of the life cycle so that the plant that you commonly think of when you think of a moss is actually the haploid phase of this organism s life cycle. Moss gametophyte and sporophyte: All the different moss plants you see growing all around in Portland are the haploid gametophyte generation of the plant. These haploid plants produce sperm and egg on specialized structures. Fertilization takes place only if there is enough water present to allow the sperm of one moss plant to swim over to the egg of the same or a different moss (many species will fertilize themselves but often there are barriers that make this less likely). After fertilization the sporophyte grows up directly from the fertilized egg and is visible as little stalks sticking up from the moss these are actually the diploid saprophyte plants that grow up out of gametophyte generation after fertilization. On the tip of the stalks are structures that produce haploid spores through meiosis. These spores are shed and if they land in an appropriate place will grow into another gametophyte. In the space on the next page sketch the two stages (gametophyte and sporophyte) of the moss life cycle. Moss Gametophyte (1n) Moss Sporophyte (2n) 9

10 Exercise 3b: Fern reproduction: In both the moss and the fern the haploid gametophyte generation is an organism that is completely separate from the diploid organism. In the moss the gametophyte generation is the dominant stage of the life cycle while in the ferns the gametophyte is a very small plant that you wouldn t normally think of as a fern at all. The fern gametophyte is usually smaller than a dime and vaguely heart-shaped. These haploid plants produce sperm and egg on specialized structures and fertilization takes place only if there is enough water present to allow the sperm of one plant to swim over to the egg of another (many species make mature sperm and egg at different times to help prevent self fertilization). After fertilization the sporophyte grows up directly from the fertilized egg and as it grows the gametophyte plant dies. The sporophyte plant that grows up is a plant that you would recognize as a fern. On the underside of some of the leaves are structures that contain cells that undergo meiosis to produce haploid spores. These spores will then be shed and can grow into the fern gametophyte once more. Look at the slides of the fern gametophyte and identify the reproductive structures. Then examine the large fern sporophyte at the back of the classroom and look for a reproductive frond covered with sori. In the left of the space below sketch a fern gametophyte and then, using a prepared slide sketch the structures that produce gametes on the right. site of female gamete production Fern Gametophyte (1n) site of male gamete production 10

11 Now in the space below sketch a fern sporophyte on the left and to the right sketch the underside of a reproductive frond (showing the sori). Fern Sporophyte (2n) spore producing structures (sori) Exercise 4 Comparing life cycles in Fungi, Plants, and Animals: Fill out the table of life cycle events for these three kingdoms. Multi-cellular organisms (all, some, or none) Cell type found in multicellular organism (haploid, diploid, and/or dikaryotic) Type of reproduction (sexual, asexual, or both) Result of meiosis (spore or gamete) Specialized gametes (yes or no) Separate haploid and diploid generations. (yes or no) Plant Fungi Animal 11