Chapter 22 The Land Plants. Cengage Learning 2016

Transcription

1 Chapter 22 The Land Plants

2 22.2 Plant Ancestry and Diversity Plants Multicelled Photosynthetic eukaryotes Adapted to life on land Close relatives of red algae and green algae Contain cellulose cell walls and chloroplasts Chlorophylls a and b Embryophytes Embryos form within chamber of parental tissues Receive nourishment during development

3 Plant Ancestry and Diversity Adaptive radiation First plants evolved 500 million years ago Photosynthetic cells had released oxygen into the atmosphere and ozone layer had formed Plant spore

4 Plant Ancestry and Diversity Plant spore Haploid cell with a cell wall Some plants have alternating generations A life cycle in which a diploid generation alternates with a haploid one Diploid Haploid

5 mitosis multicelled sporophyte zygote Diploid (2n) Phase of Cycle Fertilization Meiosis gametes Haploid (n) Phase of Cycle spores multicelled gametophyte Stepped Art

6 Major groups of plants Criteria Vascular Seed production Types of seeds produced Development and morphology

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8 Evolutionary Trends Among Plants Story of plant evolution Adapted to life on land Adapted to increasingly drier habitats Sporophyte dominates all vascular plant life cycles Spores more likely to survive in dry conditions Oak tree Large and complex sporophyte Gametophyte: only a few cells

9 Evolutionary Trends Among Plants Genetic factors Influenced sporophyte dominance Structural adaptations Cuticle Helps reduce evaporative water loss Stomata Open to allow gas exchange for photosynthesis Close to conserve water

10 Evolutionary Trends Among Plants Vascular tissues Internal system of pipelines Xylem distributes water Phloem distributes sugars Lignin provides structural support Leaves Contain veins of vascular tissue Allow plant to capture sunlight and exchange gases

11 Pollen and Seeds Pollen grains Walled, immature gametophyte Gives rise to male gametes Released by seed-bearing vascular plants Travel to female gametophytes on the wind or in insect bodies Allow plants to reproduce even in dry environments

12 Pollen and Seeds Seeds Consist of an embryo sporophyte and nutritive tissue enclosed within a waterproof seed coat Many have features that facilitate their dispersal Angiosperms disperse seeds inside a fruit

13 Bryophytes Mosses Most diverse and familiar group of bryophytes Example: Sphagnum (peat moss) 350 species One of the most economically important bryophytes Grow in peat bogs in high latitude regions of Europe, Asia, and North America Blocks are cut, dried, and burned as fuel in Ireland Helps soil retain moisture

14 zygote 7 2 sporophyte (2 n) Fertilization 6 1 gametophyte (n) Diploid (2n) phase Meiosis Haploid ( n) phase 3 1 The leafy green part of a moss is the haploid gametophyte. 2 The diploid sporophyte has a stalk and a capsule (sporangium). It is not photosynthetic. 3 Haploid spores form by meiosis in the capsule, are released, and drift with the winds. 4 Spores germinate and develop into male or female gametophytes with gametangia that produce eggs or sperm by mitosis. 5 Sperm swim to eggs. 6 Fertilization produces a zygote. 7 The zygote grows and develops into a new sporophyte while remaining attached to and nourished by the female gametophyte. sperm released from male gametangium sperm 5 egg in female gametangium male gametophyte spor e (n) released from sporangium 4 female gametophyte 2016 Cengage Learning Jane Burton/ Bruce Coleman Ltd.

15 Bryophytes Liverworts Among oldest known fossils of land plants Some gametophytes look leafy and others are flat sheets Example: Marchantia Hornworts Has a pointy, hornlike sporophyte Spores form in upright capsule called sporangium Contain chloroplasts

16 Seedless Vascular Plants Oldest vascular plant lineages Have flagellated sperm that swim to eggs Disperse by releasing spores directly to the environment Two lineages survive today Lycophytes Monilophytes

17 Seedless Vascular Plants Club mosses Often grow on floor of temperate forests Whisk ferns and horsetails Native to the Southeastern United States Includes rushes Ferns Most diverse and familiar seedless vascular plant Most live in the tropics

18 1 mature sporophyte 5 young sporophyte 1 The familiar leafy form is the diploid sporophyte. 2 Meiosis in cells on the underside of fronds (leaves) produces haploid spores. 3 After spores are released, they germinate and grow into tiny gametophytes that produce eggs and sperm. 4 Sperm swim to eggs and fertilize them, forming a zygote. 5 The sporophyte begins its development attached to the gametophyte, but it continues to grow and live independently after the gametophyte dies. Fertilization 4 zygote female gametangium male gametangium egg Diploid (2n) phase Haploid ( n) phase rhizome mature gametophyte (underside) 2 Meiosis sori (clusters of sporangia) on underside of frond 3 spore sperm photo, A. & E. Bomford/ Ardea, London; art, 2016 Cengage Learning

19 Rise of the Seed Plants Advantages of seed-bearing plants Reproductive traits Structural traits

20 pollen sac (2n) meiosis ovule (2n) meiosis microspores (n) in pollen sac develop into megaspores (n) in ovule develop into sperm-producing male gametophytes (pollen grains) release and pollination delivers sperm to egg-bearing female gametophytes in ovule fertilization zygote (2n) in ovule develop into seed (embryo sporophyte in ovule) Stepped Art Figure p365

21 Gymnosperms Vascular seed plants Produce seeds on the surface of ovules Some seeds enclosed in a fleshy or papery covering Types Conifers Cycads Ginkgos Gnetophytes

22 Gymnosperms Conifers 600 species Trees and shrubs with woody cones Needle-like or scale-like leaves with a thick cuticle More resistant to drought and cold than flowering plants Evergreen Include the longest lived plants Some bristlecone pines are 4,000 years old

23 One scale sectioned through pollen sac One scale sectioned through ovule 1 Scales of pollen cones hold pollen sacs. 4 Scales of ovulate cones contain ovules. pollen cone with many scales ovulate cone with many scales sporophyte (2n) Meiosis Meiosis 2 Meiosis of cells in pollen sacs yields microspores ( n). 9 The seed germinates and grows into a new sporophyte. 8 Fertilization produces a zygote that develops into a seed. seed coat embryo stored food zygote (2 n) seed 5 Meiosis of cells in ovules yields megaspores ( n). 3 Microspores develop into pollen grains (male gametophytes) that are released and travel on the wind. pollen tube Fer tilization eggs ( n) Inside ovule 6 Megaspores develop into eggbearing female gametophyte s inside the ovule. sperm (n) female gametophyte 7 A pollen grain alights on a scale of an ovulate cone. It germinates and a pollen tube grows toward the ovule. Sperm form as the tube grows Cengage Learning; photos, Robert & Linda Mitchell Photography; Robert Potts, California Academy of Sciences; R. J. Erwin/Science Source

24 Gymnosperms Cycads Native to dry tropics and subtropics Ginkgos One species remains today: Ginkgo biloba Native to China Deciduous Gnetophytes Tropical trees Desert shrubs Leathery vines

25 Angiosperms The Flowering Plants Vascular seed plants that make flowers and fruits Flower Specialized reproductive shoot Contain sepals, petals, and stamen Innermost part of the flower is the ovary After fertilization, ovule matures into seed Ovary becomes the fruit

26 1 An anther has two pollen sacs with diploid cells that give rise to microspores. pollen sac of anther (cutaway view) 2n ovule 4 An ovule forms on the ovary wall. It contains a diploid cell that will undergo meiosis. Meiosis 9 The ovule develops into a seed. seed coat (2n) embryo (2 n) endosperm (3 n) seed Meiosis 2 Meiosis produces microspores. 3 Microspores develop into pollen grains (male gametophytes). 7 Pollinatio n occurs, and the pollen grain germinates. A pollen tube grows to and through ovary tissue to the ovule, where it releases two sperm. mature male gametophyte microspores (n) pollen grain(n) pollination pollen tube sperm Double Fertilization pollen tube delivers 2 sperm to ovule 8 During double fertilization, one sperm fertilizes the egg to form a zygote; the other fertilizes the cell with two nuclei to form a triploid (3n) cell. megaspores (n) mature female gametophyte in ovule egg cell with 2 nuclei 5 Meiosis yields four megaspores. Three will degenerate. 6 The remaining megaspore develops into a female gametophyte tha t consists of an egg and six other cells, including a cell wit h two nuclei Cengage Learning

27 Angiosperms The Flowering Plants 90 percent of all species today are angiosperms Angiosperm characteristics that give them a selective advantage over gymnosperms Shorter life cycle Animal-pollinated flowers Enhanced seed dispersal

28 Angiosperm Diversity and Importance