Pre-lab homework Lab 3: Reproduction Across the Kingdoms - Flowers

Transcription

1 Pre-lab homework Lab 3: Reproduction Across the Kingdoms - Flowers Lab Section: Name: 1. Explain how the stages called sporophyte and gametophyte in the moss life cycle are different be sure to include whether they are haploid or diploid and what structures they develop from. 2. In flowering plants the sporophyte and gametophyte generation still are separate multicellular structures but are very different from those of the moss. What are two ways flowering plant cycles are similar to moss and what are two ways they are different? 3. What is the difference between pollination and fertilization in flowering plants and what is the role of the pollen tube? 1

2 2

3 Lab 3: Reproduction Across the Kingdoms - Flowers Lab section Name: Objectives: Upon completion of this activity, you should be able to: Contrast reproductive cycles in plants, protists, and fungi. Describe the reproductive cycle and structures of a fungus. Identify the different generations of the plant life cycle. Describe reproduction in the algae Spirogyra and Volvox. Introduction: In this lab we will continue to explore the different ways living organisms reproduce. We will investigate the structures flowering plants use to accomplish reproduction (hint: they are flowers! ), we will examine these structures to identify the remaining cells of the gametophyte generation that is much reduced in the flowering plants, and we will discuss strategies flowering plants use to insure that sperm and eggs are brought together to insure fertilization and that seeds are dispersed. We will also examine the structures of a dormant and a newly sprouted seed to see how the seeds structure is a useful adaptation for reproduction and growth. Exercise 1: Reproduction in flowering plants: While flowering plants alternate between sporophyte and gametophyte generations as do all the members of the plant kingdom there are some large differences between the flowering plants and the mosses and ferns you saw last week. One difference is that flowering plants have a separate male and female gametophyte. Another difference is that in the flowering plants the gametophyte generation is much smaller and completely retained by the sporophyte inside a structure called the flower where it is dependent on the sporophyte for nutrition. In flowering plants the male gametophyte is represented by haploid pollen grains these are actually 2- celled gametophyte plants that develop from a spore and contain a cell that will become two sperm and a cell that will grow a structure called a pollen tube. The female gametophyte in flowering plants is found inside a structure called the ovule and is an 8-celled haploid gametophyte plant that produces an egg. 3

4 Flower structures and gamete location: In flowering plants the structures that produce pollen (the male gametophyte) are called anthers and are located on top of a stalk called a filament (the anthers and filament together are called the stamen). The ovule generates spores that develop into the haploid gametophyte embryo sac inside an ovary (there may be one or many ovules inside a given ovary). The ovary itself sits at the bottom of a stalk called the style the top of which contains a widened landing pad called the stigma. Collectively the stigma, style and ovary are called the carpel. Sketch a flower (either a fresh flower or a flower model): be sure to label the following structures; carpel (includes the stigma, style and ovary), stamen (includes the anther and filament), sepals, petals, and receptacle. Cross section of anther (w/pollen) A flower the reproductive organ of a plant Cross section of ovary (w/ovules) Sketch a slide of an anther and an ovary in the boxes above: Inside the anther select diploid cells undergo meiosis to produce haploid cells called microspores. These then undergo mitosis to produce two cells known together as a pollen grain. Inside the ovule another special cell undergoes meiosis this time forming a haploid cell called the megaspore. This cell then undergoes mitosis to produce a structure called the embryo sac that is made up of 7 haploid cells. One of these cells is the egg another is a cell that has 2 haploid nuclei. These two structures (the embryo sac and the pollen) are all that remain of the gametophyte generation. 4

5 The transfer of these grains from the anther to the stigma is called pollination but this is only the first step of sexual reproduction in flowering plants. Next one of the cells of the pollen must grow a long tube down the style and into the ovule. The other cell in the pollen has now divided again to produce 2 sperm cells and one of these fertilizes the egg while the other sperm fertilizes two haploid nuclei found in the embryo sac and produces a triploid tissue called the endosperm that will serve as a nutrient supply for the young plant. Germinating pollen grains 400x A pine seed showing the embryo and the surrounding nutritive tissues In the boxes above sketch germinating pollen tubes and a pine nut that you have cut open to reveal the embryo inside: The pollen grain slide is best viewed on your microscopes with the 40x objective (this with the ocular lens gives you a total of 400x magnification). The pine nut should be viewed on a dissection scope. Notice that the pine nut is actually two different organisms the embryo in the center is the next sporophyte generation surrounded by the previous generation. Comparing Plant and Animal reproduction: Now that you have some understanding of the reproductive process that flowering plants go through answer the following questions: 1. Do plants have internal or external fertilization? Explain 2. Do plants have a dependent or independent embryo? Explain 3. What are some of the ways that plants invest in their offspring? (hint look at exercise 2) 5

6 Exercise 2: Flowering Plant Development: After fertilization the zygote develops inside the ovary of the flower. This developing zygote represents the next sporophyte generation of the plant and may be genetically very different from the flower it is developing inside. In flowering plants and conifers the zygote develops inside a structure called a seed Seeds: Grab a peanut and a germinating lima bean and split them open. Notice that in both there is a layer of tissue that surrounds the seed this is the seed coat and is what remains of the ovule. Inside the seed you see two seed leaves (called cotyledons) that are full of nutrients and food to support the growth of the early embryo. In addition you see the rest of the embryo in the peanut it is still in a state of stasis but in the bean it has started to germinate and grow sending out an embryonic root (the radicle) and the first true leaves. In the space below sketch both the peanut and the lima bean and label the seed coat, the cotyledons, the embryonic root and the embryonic leaves. (you may want to use a dissection scope) Peanut Germinating Lima bean Primary growth: Plants exhibit a growth pattern that is very different from those seen in most animals. In primary growth undifferentiated groups of cells called primary meristems divide and differentiate into the basic tissues of a plant. These meristematic regions are found at the tips of growing shoots and roots and so are responsible for increases in the length of shoots and roots. Because meristematic tissue is left at each of the branches plants always have the potential to continue growing from a large number of different places. This growth pattern, called indeterminate growth, allows plants to continue growing throughout their life. Growing shoot tip: At the tip of the growing shoot meristem is constantly undergoing division and generating new tissues that will build the organs of the plant. In the slide of the growing shoot tip you can see the early stages of leaf development and the cells building new vascular tissue as well as the bundles of meristem left behind as lateral buds. Make a sketch of a growing shoot tip showing these structures. Shoot tip 6

7 Exercise 3: Video-Sexual Encounters of the Floral Kind This video features some of the more interesting ways plants attract and utilize pollinators. While watching the video answer the following questions: In Australia, what is the pollinator for the hammer orchid? How do grasses distribute their pollen? With what do plants pay insect pollinators for their services? Why do they need to do this? Why are insects that enter an African water lily on the first day it opens often killed? Name a mammal that functions as a pollinator. 7

8 Why do Arum lilies found on islands off the coast of Sardinia bloom at the same time seabird chicks are hatching? Why do arctic rose flowers found on Greenland move during the day? What do orchid bees need from the bucket orchid to attract female orchid bees? While you saw many different examples of pollination in the video you didn t see any examples from the moss or the ferns why do you think this is? 8

9 Exercise 4: Plant pollination and fruit Flowers: One group of plants, the flowering plants, have structures (the flower) that enable it to attract animals to carry their gametes for them. Different plants have adapted to different modes ways of dispersing their pollen and by examining the structure and smell of a flower can give you a good idea of what method the organism employs. Some flowers are adapted for wind pollination others for bees and still others for flies or birds. Examine three flowers that you think have different types of pollinators, sketch them and make a hypothesis for what method of pollination they use be sure to give reasons for your hypothesis. 1. Flower 1: First sketch your first flower then make a hypothesis for its mode of pollination. Hypothesis: Reasoning: Flower 1 (magnification ) 2. Flower 2: Now sketch your 2 nd flower then make a hypothesis for its mode of pollination. Hypothesis: Reasoning: Flower 2 (magnification ) 3. Flower 3: Finally sketch your 3 rd flower then make a hypothesis for its mode of pollination. Hypothesis: Reasoning: Flower 3 (magnification ) 9

10 Fruit: To spread from one place to another plants need to use different tactics than most animals that can move. One of the tricks used by flowering plants is their ability to disperse using fruit to entice animals to move them around. Fruit develop from the tissues of the ovary of a flower (and sometimes other structures as well). 1. Simple Fruit: one flower with a single ovary may contain one or more ovules (each ovule may develop into a seed). Fruit from one ovary with one ovule 2. Aggregate fruit: One flower with many ovaries. Fruit from one ovary with many ovules 3. Multiple fruit: Many flowers fused together. Fruit from many ovaries fused together 10