Plant Reproduction and Development

Chapter 27

I. Flowers – Basic ConceptsA. reproductive structures of angiospermsB. monoecious vs. dioecious

A. monoecious: each flower has both male and female structuresB. dioecious: some individuals have “male flowers”, others “female”

C. multipurpose structures1. production of sexual spores and gametes2. site of fertilization and embryo, seed, and fruit

development3. facilitate pollination

a. transfer of pollen from one plant to another of same speciesb. functions and methods of pollination

Various Animal Pollinators

II. Flower StructureA. pedicel (peduncle): short stem that attaches flower to plantB. receptacle: base of flower from which all other parts emergeC. sepals (calyx)

1. green leaves produce sugars (photosynthesis) nourish flower2. help protect rest of flower

D. petals (corolla)1. do not photosynthesize 2. attract pollinators, if colorful and/or elaborate in shape

E. stamens1. male reproductive structures (many)2. filament3. anther

• cells divide by meiosis microspores pollen grainso male gametophytes will produce two sperm cells eacho chemical substances to attract pollinators

F. carpel (pistil)a. female reproductive structures (usually one or a few)b. stigmac. styled. ovary: contains one or more ovules

• cells in ovules divide by meiosis megaspores embryo sacso female gametophytes

each contains one egg cell + a few other cells

Fig. 27.2 Anatomy of a flower

Flower structure

G. nectaries• glands producing sugary “nectar”

H. diversity among flowers and pollen1. pollen is species-specific (why?)2. complete vs. incomplete flowers3. perfect vs. imperfect flowers

Fig. 27.6Pollen grains from (a) grass, (b) goldenrod, and (c) willow

III. The Formation of GametesA. production of male gametes (sperm)

1. diploid microsporocytes in anthers of stamens undergo meiosis2. forms four haploid microspores each3. each microspore then divides by mitosis4. this produces a haploid, 2-cell male gametophyte

• microgametophyteo pollen grains

B. pollen grains1. each consists of two cells

a. generative cell• produces two sperm cells

b. tube celli. forms the pollen tubeii. encloses the generative cell

2. surrounded by a tough outer membrane

C. production of female gametes (eggs)1. eggs are produced within ovules

a. ovules are contained within ovary of carpelb. integuments

• tough layers that surround each ovulec. micropyle

• single opening through integuments2. process

a. diploid megasporocytes in each ovule undergo meiosisb. forms 4 haploid megaspores eachc. three of these then degenerated. the surviving one divides 3 times by mitosise. produces a haploid, 7-cell female gametophyte

• megagametopyteo embryo sac

D. embryo sacs1. each consists of 7 cells

a. 6 have a single nucleus and are haploidb. 1 has 2 nuclei and is diploid

2. only cell nearest micropyle will become the egg3. cell with 2 nuclei is endosperm mother cell

• polar nuclei

Fig. 27.5 Life cycle of flowering plants

IV. FertilizationA. pollen from one flower lands on stigma of another flower

• must be of same speciesB. stages of fertilization

1. tube cell of pollen grain forms a pollen tube2. pollen tube grows down through carpel3. tube penetrates micropyle of an ovule4. generative cell of pollen grain divides to form 2 sperm cells5. the sperm travel down pollen tube

a. one fuses with the eggi. fertilization forms a diploid zygoteii. now back to sporophyte (diploid, 2n) stage

b. 2nd fuses with the 2 polar nuclei of endosperm mother celli. “double fertilization”ii. 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

C. events following fertilization1. dramatic transformations in the flower

a. zygote grows into an embryob. primary endosperm cell develops into endosperm

• surrounds and nourishes embryo while in seedc. ovule develops into a seedd. entire ovary develops into a fruit

2. remember that each ovule can be fertilized• why most fruits have many seeds

Pea flower and pea pod

V. Fruit and Seed DispersalA. necessity and functions of dispersal

1. reduces competition by separating seeds2. scatters seed to new areas and habitats

B. fruits function to disperse a plant’s seedsC. bursting apart, wind, water, animal species

Fig. 27.10 Methods of fruit and seed dispersal

Other methods of fruit and seed dispersal

VI. Asexual ReproductionA. some plants produce new individuals this wayB. most plants produce asexual structures

1. vegetative reproduction vegetative structures2. diploid structures, always formed through mitosis3. examples of vegetative structures

a. runners (stolons), rhizomes, bulbs, tubers, and “leaf shoots”b. parthenocarpy

i. development of fruits without fertilizationii. contain no embryos and no seeds (seedless fruits)

Fig. 27.12Example of asexual structure and asexual offspring

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