Chapter 2929.4Reproduction and Development in Flowering Plants
What kinds of plants do we rely on most for our food?
In this chapter, we investigate how sexual reproduction occurs in flowering plants;
Comparing sexual reproduction vs. asexual reproduction
29.1 Overview of Flowering Plant Reproduction
In plants, sexual reproduction occurs when male & female haploid gametes unite to create a diploid
zygote, which then embarks on a developmental course:
of mitotic cell division
cell enlargement, and
29.1a Diploid and Haploid Generations Arise in the Angiosperms life cycle
An angiosperm zygote develops into an embryo enclosed within a seed.
A seed is called a sporophyte(refers to the diploid, spore producing body of a plant) because the
plant tissue system begin to take place in early stages.
when one or more of the sporophyte’s shoots undergo changes in structure and function and
become reproductive shoots that give rise to a flower or an inflorescence.
Meiosis in plants give rise to haploid spores, and not gametes like animals, walled cells that
develop by mitosis into multicellular haploid gametophytes.
Male gametophytes produce sperm, and female gametophytes produce eggs.
Alternation of generations is the division of a life cycle into a diploid, spore producing.
Gametophyte vs. Sporophyte: In mosses, Gametophyte is longer lived than the sporophyte
The sporophyte grows out of the gametophyte and remains attached to and nourished by the
In angiosperms, gametophytes are reduced in sixe that they are retained inside sporophyte tissue
for all part of their lives.
The female gametophyte consists of seven cells
Male gametophyte are released in the environment as pollen grains.
The pollen grain matures when it reaches the floral tissue producing pollen tube that carries the
sperm into the egg.
Sporophytes may reproduce asexually.
29.2 Flower Structure and Formation of Gametes.
29.2a A flower consist of both sterile and fertile parts.
A flower develops from the end of the floral shoot, called the receptacle.
A flower consist of four whorls.
The two outer whorls consist of sterile organs
Outermost whorl(whorl 1) is made up of leaf like sepals.
Sepals are usually green and enclose all other parts, unopened rosebud.
Whorl(2) made up of petals
Petals play a role in pollen dispersal.
Glands that produce nectar are at the base of petals.
The other two flower’s inner whorls are reproductive organs.
Whorl(3) which male gametophytes form A stamen consists of a slender filament( stalk) capped by an anther.
Each anther is composed of four pollen sacs
Whorl (4) consist of one or more carpels, which female gametophytes form.
Lower part of carpel is the ovary
Inside the ovary consists of one more ovules.
A seed is a mature ovule.
Carper slender style widens at its upper end, terminating in the stigma, a receptive surface for
Not all plants have four whorls, these imperfect flowers are further divided according to whether
individual plants produce both sexual types of flowers or only one.
Monoecious(one) species(ex. Corn), each plant has some male flowers with only stamens and
some female flowers with only carpels.
Dioecious( two) species(ex. Willows) a plant produces flowers with only stamens or carpels.
29.2b Pollen Grains Arise from Microspores in Anthers
spores that give rise to male gametophytes are produced in anthers.
The pollen sacs inside each anther are microsporangia and contain diploid microsporocytes.
Each microsporocytes produces four small haploid microspores by meiosis.
Inside the spore wall, each microspore divides again this time mitosis.
The result is a haploid male gametophytea pollen grain.
A pollen grain consist of two cells: a larger vegetative cell that will later produce ▯ a pollen tube
and a smaller generative cell that will later divide ▯ to produce two gametes or sperm.
At maturity, a male gametophyte consist of three cells:
Two sperm calls and the tube cell
When pollen lands on a stigma, forms a pollen tube, then carries the sperm to the ovule. 29.2c Eggs and other cells of female gametophytes from megaspores in ovaries.
Each ovule consist of a stalk bearing a nucellus enveloped in additional layer of sporophyte tissue
called integuments, with an opening(the micropyle) at one end.
Inside the ovule, a diploid megasporocyte( mother cell) divides by meiosis from four haploid
First three rounds of mitosis occur without cytoplasmic division; these divisions produce a single
cell with eight nuclei, four at each pole of the cell.
Next, one nucleus in each group migrates to the center of the cell, these two polar nuclei may
fuse or remain separate.
Cell wall formation results in the formation of seven cells, three at either pole and one large central
cell containing the two polar nuclei.
Of three cells near the micropyle( the poles), one is an egg cell the other two called synergids.
At the other end of the embryo sac are three cells called antipodals,
The end result is an embryo sac containing seven cells and eight nuclei. Embryo sac is female
29.3 Pollination, Fertilization, and Germination
pollination occurs in all seed plants; it is the transfer of pollen to a female sexual structure, either a
female cone of a gymnosperm or the stigma of a flower in an angiosperm.
Gymnosperms rely on air or water currents to transport pollen, whereas pollen transfer in