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Chapter 44 Plant Reproduction and Development. How do plants reproduce? Asexually – Existing plant uses mitosis – identical – Lilac bushes that sprout.

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Presentation on theme: "Chapter 44 Plant Reproduction and Development. How do plants reproduce? Asexually – Existing plant uses mitosis – identical – Lilac bushes that sprout."— Presentation transcript:

1 Chapter 44 Plant Reproduction and Development

2 How do plants reproduce? Asexually – Existing plant uses mitosis – identical – Lilac bushes that sprout new trunks from the root – Strawberries and runners – Tulips and other bulbs grow new, smaller bulbs Sexually – Fusion of gametes from parents

3 Alternation of generations Plant sexual life cycles alternate between two multicellular stages, haploid and diploid

4 Sexual Life Cycle Sporophyte – multicellular diploid – Garden plants, produce flowers – Produces specialized reproductive cells that undergo meiosis to form haploid spores – Spores undergo mitosis to form multicellular haploid gametophyte Angiosperms and Gymnosperms produce separate male and female gametophyte stages

5 Sexual Life Cycle of a Flowering Plant 1.Diploid mother cells develop in anthers (male) or ovaries (female) 2.Meiosis produces haploid spores 3.Mitosis of the spores male & female gametophytes sperm & egg 4.Pollen carries sperm to flower, sperm travel in tube to female gametophyte 5.Fertilization diploid zygote 6.Zygote develops into embryo, seedling, mature sporophyte

6 female gametophyte male gametophyte (pollen grain) pollen tube sperm nuclei sperm female gametophyte fruit haploid (n) diploid (2n) The zygote develops into an embryo, a seedling, and eventually, a new mature sporophyte 6 A sperm fertilizes an egg within the female gametophyte, producing a diploid zygote 5 In the flower, diploid mother cells develop in the reproductive structures: anthers (male) and ovaries (female) 1 Meiotic cell division of mother cells in the sporophyte produces haploid spores 2 Mitotic cell division of the spores forms male gametophytes (pollen), which produce sperm, and female gametophytes, which produce eggs 3 flower stigma anther ovary ovule mother cell mother cellspores ovule mature sporophyte seedling embryo seed egg spores seed FERTILIZATION MEIOTIC CELL DIVISION MEIOTIC CELL DIVISION Pollen carries the sperm to the female reproductive structure of a flower; sperm travel within a pollen tube to the female gametophyte 4 Alternation of Generations

7 Sexual Life Cycle Varies between Plants Size, complexity and lifespan of sporophyte and gametophyte varies – Mosses, liverworts – gametophyte is independent – Resulting sporophyte grows on gametophyte – Ferns – sperm fertilize eggs in independent gametophyte, zygote begins growing on gametophyte but sporophyte develops its own roots and leaves – becomes dominant stage

8 Angiosperms and Gymnosperms Differ from mosses, liverworts, ferns – Diploid sporophyte is the dominant stage – In angiosperms and gymnosperms, sperm is transported within pollen grain. In mosses, liverwort and fern all require water for fertilization (sperm swim to eggs) – Gametophytes are very, very small

9 Flower Structure Flower – reproductive structure of angiosperm Complete flower – has 4 sets of modified leaves – Sepals, petals, stamens, carpels – Petunia, rose, lily

10 Complete Flower Structure Sepal – at base of flower – In monocots, resemble petals – In dicots – green and leafy – Surround and protect flower bud Petals – brightly colored, advertise for pollinators Stamens – attached above petals – Filament with anther, pollen Carpel – vase shaped, sticky stigma on elongated style, bulbous ovary at base of carpel – one or more ovules where female gametophyte develops – Fertilized ovule becomes seed and dev. into fruit (encloses)

11 sepal ovules petal filament style stigma anther ovary carpel stamen (a) A representative dicot flower A Complete Flower

12 Incomplete Flower Structure Lack one or more of 4 floral components – Grass (lack petals, sepals) – Also described as imperfect – Produce separate male and female flowers, often on a single plant (zucchini) – American holly, female produces red berries

13 Zucchini Flowers – male and female

14 Animation: Pollen Development

15 Pollen is the Male Gametophyte Develop within anthers of the sporophyte 1.Microspore mother cells develop within pollen sacs of the anther 2.Meiosis produces 4 haploid microspores 3.Each produces an immature male gametophyte (pollen grain)by mitosis, contains the generative cell – Tube cell + generative cell in the pollen cell 4.The generative cell undergoes mitosis to form 2 sperm cells.

16 Male Gametophyte Development microspore mother cell pollen sacs microspores anther sporophyte sperm cells stigma tube cell nucleus mature pollen grain Immature pollen grain tube cell cytoplasm generative cell tube cell nucleus Microspore mother cells develop within the pollen sacs of the anther of a flower 1 Meiotic cell division produces four haploid microspores 2 Each microspore produces an immature male gametophyte (a pollen grain) by mitotic cell division 3 MEIOTIC CELL DIVISION The generative cell produces two sperm cells by mitotic cell division; the male gametophyte is now mature 4 haploid (n) diploid (2n)

17 Pollen Tough, waterproof outercoat Characteristic of the plant species Used to identify climate in fossils

18 Wind-Pollinated Flowers Anther, pollen

19 Female Gametophyte Forms in ovule Species vary – one to several dozen ovules 1.Megapore mother cell develops within ovule 2.Meiosis produces 4 haploid megaspores, 3 degenerate 3.Remaining megaspore form 8 nuclei by mitosis (3X mitosis) 4.Plasma membranes form, 7 cells – 3 at one end (1 N each), one is the egg

20 A megaspore mother cell develops within each ovule of the ovaries of a flower 1 Cytoplasmic division produces the seven cells of the mature female gametophyte 4 Meiotic cell division produces four haploid megaspores; three degenerate 2 The single remaining megaspore forms eight nuclei by mitosis 3 MEIOTIC CELL DIVISION ovulemegaspore mother cell integuments megaspores central cell with two nuclei female gametophyte haploid (n) diploid (2n) egg cell ovary Female Gametophyte Development

21 Animation: Ovule Development

22 Pollination and Fertilization Pollen grain lands on stigma Absorbs water, breaks out of coat and elongates through stigma Pollen tube reaches ovule Double fertilization – both sperm fuse with cells of the female gametophyte – One sperm fertilizes egg zygote – One sperm fertilizes central cell, mitosis produces endosperm

23 Pollination and Fertilization of a Flower pollen tube tube cell nucleus sperm tube cell nucleus ovary central cell egg ovule pollen grain Pollination occurs when a pollen grain lands on the stigma of a carpel 1 A pollen tube grows down through the style of the carpel to the ovary; the tube cell nucleus travels at the tip of the tube, and the two sperm follow close behind 2 Double fertilization: One sperm fuses with the central cell One sperm fuses with the egg cell 3

24 Animation: Pollination and Fertilization

25 Fruit and Seed Development Female gametophyte and integuments become seeds Ovary becomes fruit Petals, pollen, stamens dry up and fall off

26 Development of Fruit and Seeds in a Pepper sepal ovary petal pepper flowerpepper fruits ovary wall ovule pepper fruit flesh of pepper seed ripening

27 Seed Development Three processes transform ovule into seed – Integuments become seed coat – Triploid central cell divides to form endosperm – Zygote develops into the embryo As seed matures, embryo differentiates into shoot and root – Shoot includes 1 or 2 cotyledons – absorb food from endosperm – Monocot – most of endosperm stays in seed until germination – Dicot – cotyledons absorb most of the endosperm, so the mature seed is full of embryo

28 Seed Structures Monocot – Shoot Coleoptile – sheath that surrounds embryonic leaves Dicot – Shoot Hypocotyl Epicotyl

29 integuments (diploid) seed coat central cell (triploid) endosperm (a) Early development of the seed (b) Corn seed (monocot) (c) Bean seed (dicot) fertilized ovuleseed zygote (diploid) embryo embryonic leaves embryonic root shoot endosperm seed coat cotyledon cotyledons embryonic root embryonic leaves coleoptile shoot hypocotyl seed coat Seed Development

30 Animation: Embryo and Endosperm Development

31 Germination Germination – sprouting of seed – Embryo grows and breaks out of seed – Forms seedling Warmth and moisture are necessary

32 Dormancy Some seeds have a period of dormancy – Resist adverse environmental conditions – Dormancy solves 2 problems Prevents seeds from germinating within moist fruit Environmental conditions optimal for germination may not coincide with conditions that will allow seedling to survive and mature Seeds mature in fall – in temperate climate, it isnt a good time to germinate In moist, tropical regions dormancy is less common

33 Additional Requirements for Germination Necessary to break dormancy Drying – often dispersed by fruit eating animals, excreted and dry our Cold – prolonged sub freezing temp. – ensures that seeds released in temperate weather do not germinate Seed coat disruption – weathered or partially digested before germination can occur – Desert plants have seeds that are water soluble

34 Cotyledons Nourish the Developing Plant

35 Germination Embryo absorbs water, seed coat bursts Root emerges first and grows, absorbing water and minerals Shoot cells elongate and push upward Monocots - energy comes from endosperm, digested by cotyledons and transferred to embryo Dicots – cotyledons have already absorbed endosperm so they transfer energy to embryo

36 Germination, part 2 Seeds are buried in soil and must be protected – Root tip protected by root cap – Monocot – coleoptile encloses shoot tip to protect – Dicot – shoot forms a hook, as grows clears a path for downward pointing apical meristem Cotyledons are carried out of the soil, become green and photosynthetic, transfer stored and new food to shoot True leaves take over photosynthesis, cotelydons die back

37 Seed Germination root hypocotyl hook root seed coat cotyledons cotyledon hypocotyl epicotyl withered cotyledons true leaves coleoptile true leaves (b) Bean (dicot) (a) Corn (monocot)

38 Plants and their Pollinators Coevolution – each as acted as an agent of natural selection on the other Some flowers provide food – Beetles, moths, butterflies, hummingbirds – Animals distribute pollen – Flower colors have coevolved to match the color vision of the animal Bees see UV light so flowers are white, blue, yellow, orange Marking s that point to the center of the flower Structural adaptations - nectar containing tubes, stamens, smell, etc.

39 UV Patterns Guide Bees to Nectar near UV 400 bee visionhuman vision violetbluegreenyelloworangered far- red wavelength (nm) human bee (a) A comparison of color vision in humans and bees (b) Flower color patterns seen by humans and bees

40 Pollinating a Pollinator

41 Vertebrate Pollinators Hummingbirds need a lot of energy so the flowers they pollinate produce more nectar than flowers that are pollinated by insects.

42 Mating Decoys Particularly orchids Mimic female wasps, bees or flies in smell and shape. Males attempt to copulate but only pick up pollen packet which transfers to the next flower

43 Nurseries for Pollinators Some insects pollinate the flower, then lay their eggs in the flowers ovary – Milkweed and milkweed bugs – Yucca and yucca moth Visit – collect – visit and drill hole, lay eggs – pollinate stigma with pollen Neither can reproduce without the other

44 Fruit helps disperse seeds Disperse seeds far away so there is no competition Adult plants can withstand more damage than seedlings Species will be more successful if they disperse their seeds a distance Many different types of dispersal Seed dispersion methods

45 Water-Dispersed Fruit

46 Wind-Dispersed Fruits

47 Clingy Fruits

48 Colored fruit attracts animals Blackberries, raspberries, strawberries, tomatoes, peppers - small seeds that animals swallow – Eventually excreted unharmed – Some seed coats must be scraped or weakened by an animals digestive tract before germination – Transported away from its parent plant and ends up with is own fertilizer! – Seed dispersal video Seed dispersal video


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