Plant Reproduction and Development - PowerPoint Presentation

Plant Reproduction and Development Chapter 27

Flowers – Basic Concepts reproductive structures of angiosperms monoecious vs. dioecious monoecious : each flower has both male and female structures d ioecious : some individuals have “male flowers”, others “female” multipurpose structures production of sexual spores and gametes site of fertilization and embryo, seed, and fruit development facilitate pollination transfer of pollen from one plant to another of same species functions and methods of pollination

Various Animal Pollinators

Flower Structure pedicel ( peduncle) : short stem that attaches flower to plant r eceptacle : base of flower from which all other parts emerge sepals ( calyx) green leaves  produce sugars (photosynthesis)  nourish flower help protect rest of flower petals ( corolla) do not photosynthesize attract pollinators, if colorful and/or elaborate in shape s tamens male reproductive structures ( many) filament a nther cells divide by meiosis  microspores  pollen grains male gametophytes  will produce two sperm cells each chemical substances to attract pollinators carpel ( pistil) female reproductive structures (usually one or a few) s tigma s tyle o vary : contains one or more ovules cells in ovules divide by meiosis  megaspores  embryo sacs female gametophytes each contains one egg cell + a few other cells

Fig. 27.2 Anatomy of a flower

Flower structure

n ectaries glands producing sugary “ nectar” diversity among flowers and pollen pollen is species-specific (why ?) complete vs. incomplete flowersperfect vs. imperfect flowers Fig. 27.6Pollen grains from (a) grass, (b) goldenrod, and (c) willow

The Formation of Gametes production of male gametes ( sperm) diploid microsporocytes in anthers of stamens undergo meiosis forms four haploid microspores eacheach microspore then divides by mitosisthis produces a haploid, 2-cell male gametophytem icrogametophyte pollen grains pollen grains each consists of two cells generative cell produces two sperm cells tube cell forms the pollen tube encloses the generative cell surrounded by a tough outer membrane

production of female gametes ( eggs) eggs are produced within ovules ovules are contained within ovary of carpel integuments tough layers that surround each ovule micropylesingle opening through integumentsp rocess diploid megasporocytes in each ovule undergo meiosis forms 4 haploid megaspores each three of these then degenerate the surviving one divides 3 times by mitosis produces a haploid, 7-cell female gametophyte m egagametopyte embryo sac embryo sacs each consists of 7 cells 6 have a single nucleus and are haploid 1 has 2 nuclei and is diploid only cell nearest micropyle will become the egg cell with 2 nuclei is endosperm mother cell polar nuclei

Fig. 27.5 Life cycle of flowering plants

Fertilization pollen from one flower lands on stigma of another flower must be of same species stages of fertilization tube cell of pollen grain forms a pollen tubepollen tube grows down through carpel tube penetrates micropyle of an ovule generative cell of pollen grain divides to form 2 sperm cells the sperm travel down pollen tube one fuses with the egg f ertilization  forms a diploid zygote now back to sporophyte (diploid, 2n) stage 2 nd fuses with the 2 polar nuclei of endosperm mother cell “double fertilization” forms a triploid (3n) primary endosperm cell

Fig. 27.5 Life cycle of flowering plants

Close-up of fertilization in flowering plants

Fig. 27.5 Life cycle of flowering plants

events following fertilization dramatic transformations in the flower zygote grows into an embryo primary endosperm cell develops into endosperm surrounds and nourishes embryo while in seedovule develops into a seed entire ovary develops into a fruit remember that each ovule can be fertilized why most fruits have many seeds Pea flower and pea pod

Fruit and Seed Dispersal necessity and functions of dispersal reduces competition by separating seeds scatters seed to new areas and habitats fruits function to disperse a plant’s seedsbursting apart, wind, water, animal species Fig. 27.10 Methods of fruit and seed dispersal

Other methods of fruit and seed dispersal

Asexual Reproduction some plants produce new individuals this way most plants produce asexual structures vegetative reproduction  vegetative structuresdiploid structures, always formed through mitosisexamples of vegetative structures runners ( stolons ), rhizomes , bulbs , tubers, and “leaf shoots” p arthenocarpy development of fruits without fertilization contain no embryos and no seeds (seedless fruits) Fig. 27.12 Example of asexual structure and asexual offspring

Fig. 24.19 Different kinds of asexual, vegetative structures. These are all modified stems.