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Chapter 5: Plant Life Cycle: Flowers (Pollination and Fertilization (Wind…
Chapter 5: Plant Life Cycle: Flowers
The Flower
Floral Organs
outermost whorl consists of sepals, usually green and photosynthetic
calyx
:
collective term for sepals of a flower
corolla
:
collective term for the petals of a flower
petals often brightly colored and conspicuous
function by attracting animal pollinators
calyx and corolla together are the perianth
perianth
:
the petals and sepals together
in center of flower, find male and female structures
androecium
:
(pl: androecia) collective term for all the stamens in a flower
whorl of male structures
each androecium consists of of pollen-producing anthers supported on a stalk
anther
:
pollen-producing part of a stamen
filament
:
part of the stamen in a flower that supports the anther
each anther houses four chambers, where pollen develops
pollen
:
immature male gametophytes of seed plants
gynoecium
:
(pl: gynoecia) collective term for the carpels in a flower
whorl of female structures, aka carpels, located in middle of flower
flowers can have one or more carpels; if many, could be fused together or separate
carpels consist of stigma, style, and ovary
stigma
:
the receptive portion of the carpel to which the pollen adheres
style
:
the tissue that connects the stigma to the ovary in the carpel
ovary
:
enlarged basal portion of a single carpel or several fused carpels; contains one to many ovules
within ovary are one or many ovules
ovule
:
structure that will become a seed after fertilization; an integumented megasporangium that contains the embryo sac before fertilization
rising from ovary is slender column called style
expanded tip of style is stigma, which functions in receiving pollen
complete flower
:
a flower with all four floral whorls (sepals, petals, stamens, and carpels)
some flowers may have additional floral structures called bracts
bract
:
a floral leaf
found outside the calyx
may appear leaflike or petallike and be of various sizes
there are easily recognizable differences in floral structures
monocots generally have floral parts in threes or multiples of three
dicots generally have a numerical plan of four to five or multiples
Modified Flowers
basic pattern of flower structure often modified
tepal
:
members of the perianth that are not differentiated into sepals and petals
ex- lilies and tulips, in which sepals and petals are identical
tepals refers to the sepals and petals together
petals can also be partly or completely fused together (forming corolla tube), sepals can be partially or completely fused (forming calyx tube), and flowers of grasses possess neither sepals nor petals (incomplete flowers)
incomplete flower
:
flower lacking one or more floral whorls; typically, either the sepals, petals, or both
perfect flowers
:
a flower having both stamens and carpels
even if sepals or petals are missing
some flowers are unisexual, are either staminate or carpellate
staminate flower
:
a flower having stamens but no carpels
carpellate flower
:
a unisexual flower that contains carpels but no stamens
imperfect flower
:
unisexual flower; either staminate or pistillate
some plants have both staminate and carpellate flowers
monoecious
:
refers to a plant species whose separate male and female reproductive structures are borne on the same plant; pollen-bearing and ovule-bearing flowers or cones are borne on the same plant
as opposed to monoecious, some plants have only unisexual flowers
dioecious
:
refers to a plant species that has separate male and female plants; pollen-bearing and ovule-bearing flowers or cones are borne on different plants
position of ovary in relation to other floral parts important for classification of flower
superior ovary
:
an ovary located above the sepals, petals, and stamens
inferior ovary
:
ovary that lies below the attachment of the sepals, petals, and stamens; an epigynous flower
hypogynous
:
floral whorls (sepals, petals, stamens) inserted below the ovary of a flower
flower parts below the superior ovary
epigynous
:
refers to a plant whose floral parts (sepals, petals, and stamens) appear to arise from the top of an ovary; the ovary is said to be inferior
flower parts inserted above the inferior ovary
perigynous
:
refers to a flower in which the bases of the sepals, petals, and stamens form a cup around the ovary
bases of flower parts fused into cup-like structure surrounding a superior ovary
flowers can be described in terms of symmetry
actinomorphic
:
(regular flower) regular or radially symmetric
zygomorphic flower:
(irregular flower) a bilaterally symmetrical flower, capable of being divided into two symmetrical halves only by a single longitudinal plane passing through the axis
some flowers (solitary flowers) borne singly on stalk, but usually flowers grouped together
inflorescences
:
a cluster of flowers
sometimes what is usually called single flower is actually inflorescence
arrangement of flowers in cluster determines the type of inflorescence
spike
:
an inflorescence in which the main axis is elongated and the flowers are sessile
raceme
:
a vertical inflorescence with stalked flowers
panicle
:
a branched inflorescence with the branches bearing loose flower clusters
umbel
:
a flat-lopped inflorescence in which the stalked flowers all radiate out from a common point
head
:
horizontal inflorescence of sessile flowers
catkin
:
inflorescence of unisexual flowers
flowers play pivotal role in life cycle of angiosperms, since they are the sites of sexual reproduction
flowers, unique to angiosperms, are essentially modified branches bearing four sets of specialized appendages or floral organs
appendages grouped into whorls and consist of these whorls, from outermost to innermost
sepal
:
a leaflike floral organ that protects the unopened flower bud
petal
:
a floral organ that is leaflike and often brightly colored; a component of the corolla
stamen
:
the floral organ that produces pollen; consisting of an anther and filament
carpel
:
the ovule-bearing part of the flower
appendages inserted into the receptacle, the expanded top of the pedicel or peduncle
receptacle
:
the expanded tip of a pedicel or peduncle to which the floral organs are attached; also, swollen areas at the end of the blade that function as reproductive regions in certain members of the brown algae
pedicel
:
an individual stalk of a flower that is part of an inflorescence
peduncle
:
the main stalk of a flower that is part of an inflorescence
Mad About Tulips
the flower, characteristic of angiosperms, technically is a modified branch bearing specialized leaves that are integral to sexual reproduction
Ottoman court favored tulips with elongated, pointed petals
first arrived in Europe in 1554
wild tulips originated in central Asia
monocots belonging to the lily family (Liliaceae)
about 120 species of tulips, usually with one flower on a stalk
most have three sepals and three petals apiece, six stamens, and a central gynoecium of three carpels
shape of flower and petals vary
can produce seeds, but takes 7 years before a tulip grown from seed will flower
faster to grow it from bulbs (an underground stem with fleshy storage leaves
as bulb grows, produces 2-4 new bulbs within the layers, or skirts, of the original bulb
bulbs can be divided and planted and flower within a few months of a single growing session
characteristics of parent plant remain, since it is asexual reproduction
part of fascination with tulips has to do with phenomenon called breaking
2-3 out of every 100 tulips prone to spontaneous, unpredictable eruptions of color, with stripes or feathers of bold color against a contrasting background
caused by tulip breaking virus spread by the peach-potato aphid, an insect that sucks the sap out of plants
color of tulips is due to two types of pigment
base color is either white or yellow and red or blue anthocyanin pigments; these two combine to create final color
Meiosis
Stages of Meiosis
Prophase I
at beginning, chromosomes appear threadlike and DNA is duplicated in S phase of preceding interphase, so that each chromosome consists of two chromatids
as chromosomes continue to condense/coil, homologous chromosomes pair up in synapsis
synapsis
:
the pairing of homologous chromosomes that occurs in prophase I of meiosis
consists of four chromatids since each chromosome is doubled
breaks and exchanges of genetic material can occur between chromatids as synapsed chromosomes continue to condense
crossing over
:
the exchange of genetic material between chromatids of homologous chromosomes during prophase I of meiosis
results in chromatids that are complete but have new genetic combinations
soon, synapsis breaks down and homologous chromosomes break apart at all places except where crossing over occurred
chiasma
:
(pl: chiasmata) the X-shaped configuration between the chromatids of homologous chromosomes that have exchanged genetic material during prophase I of meiosis
while chromosome events occurring, nucleolus and nuclear membrane break down, leaving chromosomes free in cytoplasm
longest and most complex stage of meiosis
Metaphase I
homologous chromosome pairs line up at equatorial plane (across center of cell)
spindle fibers that began to form in late prophase attach to centromeres of each homologous pair
Anaphase I
homologous chromosomes separate
pulled by spindle fibers to opposite poles of cell
chromosomes from each parent mixed randomly into number of possible combinations during separation process
chromatids of each chromosome still united, only homologous pairs separate
by end of phase, chromosome number has been halved
Telophase I
the spindle disappears, chromosomes become less distinct, and nuclear membrane may re-form
generally followed by cytokinesis, dividing cell into two daughter cells, each with half the number of chromosomes of original parent cell
Second Meiotic Division
in some organisms, interphase occurs between two meiotic divisions, but in other cases, cells proceed directly from telophase I to prophase II
second meiotic division essentially similar to mitosis- chromatids are still joined together and finally separate
prophase II identical to mitotic prophase where, in each cell, chromosomes become evident and nuclear membrane breaks down
during metaphase II, chromosomes line up at equatorial plane of each cell and spindles appear, with spindle fibers stretching from pole to pol and pole to centromere
during anaphase II, chromatids separate, pulled to poles by spindle fibers
in telophase II, cytokinesis occurs and nuclear membrane and nucleoli reappear as single-stranded chromosomes become threadlike chromatin
by end of telophase II, four haploid cells produced, which contain unique genetic combination, different from each other and from parent
meiosis is specialized form of cell division that consists of two consecutive divisions and results in the formation of four haploid cells
both first and second division divided into four stages
during first meiotic division, chromosome number is halved
meiosis
:
two successive nuclear divisions during which the chromosome number is halved; in plants, meiosis results in the formation of spores
occurs within stamens and carpels
sexual reproduction (in plant or animal) basically fusion of male and female gametes (sperm and egg), which produce zygote
gamete
:
sex cell
zygote
:
a diploid cell that is formed by the fusion of two gametes
when egg fertilized by sperm, zygote receives equal number of chromosomes from each gamete, which are different from other cells in angiosperm because gametes each have only one set of chromosomes
haploid
:
one set of chromosomes in a cell; 1N
diploid
:
two complete sets of chromosomes in a cell; 2N
during process of fertilization, diploid number restored in zygote
in diploid cell, there are two of each kind of chromosome
homologous chromosomes
:
chromosome pairs of the same size and shape that carry genes fo the same traits
members of pair derived from contributing haploid gametes
meiosis important because reduces the number of chromosomes from diploid to haploid, compensates for the doubling that occurs during fertilization
product of meiosis in plants are haploid spores
spore
:
a reproductive unit (often unicellular) that is capable of developing into a new organism without fusion with another cell
formed in sporangium
diploid plant that undergoes meiosis to form spores called sporophyte
sporophyte
:
a diploid plant that produces spores; the diploid phase of a life cycle that has an alternation of generations
spores develop into haploid gametophytes, that produce gametes, egg, or sperm
gametophytes
:
haploid generation of plants that produce gametes
sporophyte and gametophyte are the two stages in the life cycle of each plant
process of fertilization brings together egg and sperm to provide genetically unique zygote
Meiosis in Flowing Plants
Male Gametophyte Development
during development of stamen, certain cells in pollen chambers of anther become distinct as microspore mother cells
microspore mother cells
:
diploid cell in microsporangium that undergoes meiosis to produce microspores
pollen chambers referred to as microsporangia
microsporangium
:
sporangium that contains microspores
each microspore mother cell undergoes meiosis to produce four microspores (male spores), which initially stay together as tetrad, but eventually separate and each forms into pollen grain, an immature male gametophyte
microspore
:
spore that develops into male gametophyte
tetrad
:
a group of four, such as the four haploid spores that form after meiosis, or the four chromatids in a bundle after homologous chromosomes pair
in development of pollen grain, the microspore undergoes a mitotic division to produce two cells
generative cell
:
cell in male gametophyte (pollen grain) that divides, produces two sperm
vegetative cell
:
the cell in the pollen grain that develops into the pollen tube
wall of microspore becomes chemically and structurally modified into the pollen wall, consists of inner layer and outer layer, which may be ornamented with spines, ridges, or pores
intine
:
the inner layer of the pollen wall
exine
:
the outer layer of the pollen wall
when pollen grains fully developed, released as anthers open, or dehisce
Female Gametophyte Development
within the ovary, one or more ovules develop, which consists of a megasporangium enveloped by one or two layers of tissue called integuments
megasporangium
:
sporangium that contains megaspores
integument
:
outermost layers of an ovule that typically develop into the seed coat
integuments completely surround megasporangium except for micropyle
micropyle
:
the opening in an ovule though which the pollen tube enters during fertilization
ovary first appears as bulge in ovary wall, then during development one cell becomes distinct as megaspore mother cell, which is surrounded by tissue called nucellus
megaspore mother cell
:
diploid cell in megasporangium that, upon undergoing meiosis, yields megaspores
nucellus
:
tissue in the ovule within which the embryo sac develops; integuments surround the nucleus
megaspore mother cell undergoes meiosis to produce four megaspores, three of which generally degenerate
megaspore
:
spore that develops into the female gametophyte
megaspore then undergoes series of mitotic divisions, eventually producing a mature female gametophyte, called embryo sac
embryo sac
:
female gametophyte of angiosperms; retained within the ovule
in typical pattern of development, series of three mitotic divisions produces eight nuclei within the greatly enlarged megaspore
eight nuclei distributed with three egg apparatus near micropyle end of ovule, three antipodals at opposite end, and two polar nuclei in enter
egg apparatus
:
egg cell and adjacent synergids in the embryo sac (female gametophyte) of angiosperms
consists of two synergids and one egg
synergid
:
one of a pair of short-lived cells that lie close to the egg in the mature embryo sac
egg
:
nonmotile female gamete
antipodals
:
one of several cells (usually three) of the embryo sac (female gametophyte) of angiosperms; located opposite the egg and synergids
polar nuclei
:
two nuclei found in the embryo sac that unite with a sperm to form the primary endosperm nucleus
cell walls develop around egg, synergids, and antipodals, producing the mature female gametophyte
within flower, meiosis occurs during the formation of pollen in the anthers and stamen and the formation of ovules within the ovary of the carpel
Pollen is More than Something to Sneeze At
palynology is the study of pollen
when pollen released by wind-pollinated plants (either gymnosperms or angiosperms), only a tiny percentage reaches the receptive female organ
the distinctive ornamentation of the outer wall of a polled grain allows for the identification of most types of pollen to the genus level
under certain conditions, polled can be preserved and leave a record of climate conditions
can indicate whether area is rich in oil
examination of fossil pollen can indicate when shift from gathering native vegetation to cultivating cereal grain tool place
Pollination and Fertilization
Animal Pollination
color and scent are what attract animals to flowers
certain colors associated with specific pollinators
nectar guide
:
color patterns present on petals that direct insects toward the nectar; often not visible to the human eye
essential oil
:
volatile component that contributes to the scent and flavoring of aromatic plants
in most cases, flower attracts animal with nectar, pollen, or both
nectar
:
a sugary solution that attracts animals to plants
nectary
:
a gland that secretes nectar
found in the epidermis of a floral organ
flowering plants and pollinating animals are example of coevolution
coevolution
:
the interaction of species as selective forces upon each other, resulting in adaptations that enhance their interdependency
adaptations occur that make flower more attractive to pollinator, who changes in ways that enhance efficiency in exploiting nutritional rewards offered by the flower
Honey Bees and Colony Collapse Disorder
approximately 25% of US diet comes from crops pollinated by honey bees
beginning in 2006, significant losses of honey bees in their hives, losses of 30-50%
colony collapse disorder
:
sudden loss of honey bees from their hive, often leaving just a queen bee and a few workers; the cause is uncertain with viruses, mites, and insecticides implicated in the phenomenon
Wind Pollination
wind-pollinated flowers, as opposed to animal-pollinated, have much simpler structure, don’t require as much color, nectar, fragrance
wind-pollinated flowers usually small and inconspicuous, usually lacking petals and sometimes even sepals, frequently arranged in inflorescences
most grasses have perfect flowers, but many other wind-pollinated species are imperfect
stamens and stigmas modified for this method of pollination
filaments usually are long, allowing anthers to hang freely, away from flower
stigmas often feathery, increasing the surface area for trapping pollen
small size offset by large number of flowers form and production of copious amounts of dry, lightweight pollen
Double Fertilization
once pollination accomplished, stage set for fertilization
pollen grain at time of pollination contains tube cell and generative cell
on compatible stigma, pollen grain germinates, pollen tube begins to grow down into the style toward the ovary
pollen tube
:
a tube that develops from the pollen grain and carries the sperm to the ovule
vegetative nucleus generally found at the growing end of the pollen tube while behind it, the generative nucleus divides mitotically, producing two nonmotile sperm
pollen tube continues to grow until it reaches and grows into micropyle of an ovule, penetrating the ovule at one synergid
vegetative nucleus, synergids, and antipodals usually degenerate during the fertilization process, leaving the two sperm, egg, and polar nuclei as the remaining participants
both sperm involved in fertilization
one sperm fertilizes the egg to produce a zygote that will develop into an embryo
embryo
:
immature sporophyte that develops from a zygote
zygote produced from the fusion of the haploid egg and sperm is diploid, restores chromosome number for sporophyte generation
second sperm fertilizes or fuses with the two polar nuclei, producing a primary endosperm nucleus, which develops into endosperm, a nutritive tissue for the developing embryo
primary endosperm nucleus
:
the product of the fusion of a sperm and two polar nuclei in the embryo sac of angiosperms; double fertilization
endosperm
:
nutrient tissue that forms by the fusion of a sperm nucleus with two polar nuclei during double fertilization in angiosperms
fusion of the haploid sperm and polar nuclei usually procure triploid endosperm
triploid
:
refers to a cell or a nucleus that contains three sets of chromosomes; common in endosperm
endosperm generally begins immediately, followed by division of the zygote to produce the embryo
double fertilization
:
the fusion of egg and sperm resulting in a zygote, and the simultaneous fusion of sperm with two polar nuclei resulting in the formation of endosperm that characterizes all angiosperms
distinctive feature of angiosperm production
nutritive value of many foods due to the large endosperm reserves in these grains
after fertilization, changes begin to occur in whole flower
sepals, petals, and stamens often whither as ovary expands and becomes a fruit
fruit
:
a ripened ovary of an angiosperm flower
within ovary, each fertilized ovule becomes a seed, containing an embryo and nutritive tissue
seed
:
a mature ovule containing an embryo and food supply and covered by a seed coat
the integuments of the ovule develop into the seed coat
seed coat
:
the outer layer of a seed that is developed from the integuments of the ovule; the testa
fruit occasionally forms without fertilization
parthenocarpy
:
development of fruits without fertilization resulting in seedless fruits
pollination
:
the transfer of pollen from an anther to a stigma
self-pollination
:
transfer of pollen from stamen to stigma within the same flower or plant
cross-pollination
:
transfer of pollen from the stamen to the stigma of a flower of another plant
prevents the effects of inbreeding and most perfect flowers have physiological mechanisms to prevent self-fertilization
large, showy flowers usually attract animal pollinators, whereas small, inconspicuous flowers are often wind-pollinated
Alluring Scents
fragrances of plants, due to their essential oils, values as source of perfumes
many current perfumes are synthetics that resemble natural essences from plants, but many expensive perfumes still rely on natural essential oils extracted directly from plants
different methods used to extract essential oils from plants, method determined by location and chemical properties of essential oil