ALE 4 Plants – BSC2011, Spring 2020

In-Class Active Learning Exercise: Seedless and Seed Plants

Introduction: Land plants acquired traits that made it possible to colonize land and survive out of the water. All land plants share the following characteristics: alternation of generations, with the haploid plant called a gametophyte, and the diploid plant called a sporophyte; formation of haploid spores in a sporangium; formation of gametes in a gametangium; protection of the embryo; and an apical meristem. Nonvascular seedless plants do not possess vascular conductive tissue to transport water and glucose, therefore they are very small and live in moist environments. Vascular seedless plants have an additional adaptation of conductive vascular tissue, xylem and phloem. Vascular plants are not limited in size and can inhabit drier environments. All land plants possess a waxy cuticle that prevents desiccation, and a tough sporopollenin layer that protects the spores. Land plants appeared about 500 million years ago in the Ordovician period.

Objectives: • Learn vocabulary pertinent to plant structure • Understand Alternation of Generations in both seedless and seed plants • Distinguish between gametophytes and sporophytes in both seedless and seed plants • Describe plant stem and root anatomy • Describe differences between gymnosperm and angiosperm life cycles • Explain double fertilization in angiosperms

Preparation related to the two assignments on this worksheet: • Read Chapters 25, 26, 30, and 32 • Answer the pre-lecture questions on Chapters 25, 26, 30, and 32 • Attend the lectures on Chapters 25, 26, 30 and 32 and actively participate in iClicker questions

Grading: You have ~25 minutes to work through this worksheet in small groups. Afterwards, you’ll get 10 iClicker questions that you will have to answer individually. Each question is worth 1 point: 0.5 point participation + 0.5 point correct answer. These points contribute to your overall iClicker score, which is 10% of your final grade.

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Assignment 1: Bryophyte Structure (~7 mins) Bryophytes are small, seedless, nonvascular plants. They are the closest living relatives of the earliest land plants. They undergo Alternation of Generations with a dominant gametophyte stage. As nonvascular plants, they do not have true leaves or stems and they do not have conductive vascular tissue. Bryophytes include liverworts, hornworts, and mosses.

1A Bryophyte Alternation of Generations Bryophytes have an alternation of generations life cycle in which the haploid gametophyte is the dominant stage. The gametophyte produces gametes which form a sporophyte upon fertilization. The sporophyte produces haploid spores which germinate into a gametophyte. Label each box as mitosis or meiosis. Label each of the following as diploid (2n) or haploid (n): gametophytes, sperm, egg, zygote, sporophytes, and spores.

1. In seedless plants, a fertilized egg will develop into a. A gametophyte b. A fruit c. A sporophyte d. Gametes e. Spores

2. The diploid generation of the plant life cycle always a. Is larger and more conspicuous than the haploid generation b. Is called the gametophyte c. Develops from a spore d. Produces spores e. Produces eggs and sperm

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1B Life Cycle of Mosses Arrange the events in the life cycle of mosses in the flowchart below. Start the life cycle with the mature sporophyte stage in target 1. Not all labels will be used.

1C Terrestrial Plant Adaptations 1. Which of the following traits was the most important in enabling the first plants to move onto land? a. Rings of cellulose synthesizing complexes b. Alternation of Generations c. Apical meristems d. Development of sporopollenin to prevent desiccation of the zygote e. Peroxisome enzymes that minimize losses from photorespiration

2. What evolutionary development allowed terrestrial plants to grow tall? a. Sporophylls b. Waxy cuticle c. Rhizoids d. Leaves e. Lignified vascular tissue

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Assignment 2: Plant Structure (~5 mins) 2A Building vocabulary Learning common prefixes and root words assists learning complex plant vocabulary.

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2B Stems Vascular plants have conductive vascular tissue, xylem and phloem. Xylem cells transports water and dissolved minerals upward from the roots to the leaves of the plant. Phloem cells transport glucose from the leaves to various parts of the plants. Monocots are the grasses; they have parallel leaf venation and fibrous roots. Cross sections of monocot stems and roots show scattered vascular bundles. All other plants are Eudicots (sometimes called dicots); they have branched leaf venation and a main taproot. Cross sections of eudicots show vascular bundles that form a ring. 1. Label the parts of the stems

2. The primary growth of a plant adds ______and the secondary growth adds ______. a. Height, branching b. Branching, girth c. Girth, height d. Branching, flowers e. Height, girth

3. Label the areas of the root

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4. Cell division in the roots occurs in the ______. a. Root cap b. Area of Elongation c. Apical Meristem d. Area of Maturation

Assignment 3: Seed Plants (~10 mins) Seed plants are vascular plants with a dominant diploid sporophyte stage. Two major innovations of seed plants are seeds and pollen. Seeds protect the embryo from desiccation and provide it with a store of nutrients to support the early growth of the sporophyte. Seeds are also equipped to delay germination until growth conditions are optimal. Pollen allows seed plants to reproduce in the absence of water.

In the gymnosperms pollen is dispersed by wind, and their naked seeds developed in the sporophylls of a strobilus. Angiosperms bear both flowers and fruit. Flowers expand the possibilities for pollination, especially by insects. Fruits offer additional protection to the embryo during its development. Angiosperms have become the dominant plant life in terrestrial habitats.

3A Gymnosperm Life Cycle Gymnosperms have male cones and female cones. The male cones contain microsporangia that produce haploid microspores via meiosis. Each microspore undergoes mitosis to produce two nuclei, the generative nucleus and the tube nucleus, which is pollen, the male gametophyte. The female cones contain megasporangia that contain megaspore mother cells which produce four haploid megaspores via meiosis. One megaspore divides via mitosis to produce the female gametophyte, the other three divide to produce the archegonia. Label the diagram

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3B Gymnosperm Reproduction 1. In pine trees, the embryo develops within the ______. a. Macrogametophyte b. Pollen cone c. Female gametophyte d. Male gametophyte e. Microsporophyll

3C Angiosperm Life Cycle 2. Angiosperms are different from all other plants because only they have ______. a. A vascular system b. A life cycle that involves alternation of generations c. Seeds d. Flowers e. A sporophyte phase

3. The major difference between angiosperms and gymnosperms come from the a. Production of microspores versus megaspores b. Presence or absence of a protective covering over the ovule c. Presence or absence of vascular structures d. Dominance of sporophyte in angiosperms and gametophyte in gymnosperms e. Presence or absence of alternation of generations

3D Flower Structure Label the parts of the flower

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3E Angiosperm Life Cycle Some angiosperm flowers contain both female and male reproductive structures. The male anther contains microsporangia which produce microspore mother cells. These mother cells produce haploid microspores (pollen) via meiosis. Then each pollen divides via mitosis to produce a pollen tube cell and a generative cell. The female carpel contains megasporangia which produce megaspore mother cells. These mother cells produce 4 haploid megaspores via meiosis. One lives and the other three die. That one then undergoes mitosis without cytokinesis to produce a gametophyte with seven cells and eight nuclei. Two of the nuclei fuse to form a single diploid polar body. Angiosperms undergo double fertilization to produce the zygote and the endosperm which provides nutrition to the zygote. When the pollen lands on the stigma, one of the cell, the pollen tube cell germinates and grows through the style to reach the ovule. The other pollen cell, the generative cell, divides to form two sperm cells. One sperm cell fertilizes the egg to form the zygote, the other sperm cell joins with two polar nuclei in the ovule to form the endosperm.

4. Which of these is unique to flowering plants? a. Pollen production b. Dominant sporophyte c. Double fertilization d. Embryo surrounded by nutritive tissue e. Haploid gametophytes 5. In angiosperms, each pollen grain produces two sperm. What do these sperm do? a. Each one fertilizes a separate egg cell b. One fertilizes an egg, the other combines with two polar nuclei which develop into the endosperm c. One fertilizes an egg, the other fertilizes the fruit d. Both sperm fertilize a single egg e. One fertilizes and egg, the other is kept in reserve

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