Flowers and Reproduction (Angiosperms)
Asexual Reproduction
fragmentation
individual parts become self sufficient
Sexual Reproduction
flowers
produce the necessary reproductive cells and structures
The Plant Life Cycle
gametes=mammal or spores=plants
haploid sex cells
produced by meiosis
sperm (microgametes)
egg (megagametes)
produced by males
produced by females
zygote= sperm + egg
sporophyte phase
a.k.a. sporophyte generation
diploid phase of plant life cycle
organs (located in the flowers)
capable of undergoing meiosis
produce spores
do not undergo syngamy
syngamy or fertilization
the fusion of gametes
undergo mitosis
grows into new haploid plant (gametophyte)
microgametophytes=male
megagametophytes=female
from microspores
from megaspores
plant (-phyte)
gametes (gameto-)
heterospory
having two types of spores
alteration of generations
life cycle with two generations
sporophyte
gametophyte
gametophytes do not resemble sporophytes
alteration of heteromorphic generations
complex life cycle
3 distinct plants
1 sporophyte
2 gametophytes
Flower Structure
basically a stem with leaf-like structures
never become woody
secondary growth does not occur
pedicel
a flowers stalk
receptacle
very end of axis
other flower parts are attached
four types of floral appendages:
sepals
petals
stamens
carpels
lowermost and outermost appendage
modified leaves
enclose/ surround other flower parts
typically thickest, toughest, and waxiest flower part
protect bud as it develops
calyx
all the sepals together
above the sepals on receptacle
"leaf-like"
corolla
all petals together
perianth
sepals and petals together
contain pigments instead of chlorophyll
attract correct pollinators
distinct size, shape, color, and arrangement
above the petals
androecium
all of the stamens together
technically not "male"
produce pollen
two parts:
filament
anther
its stalk
composed of diploid cells
four columns of of tissue become distinct
some cells enlarge
prepare for meiosis
microspore mother cells
a.k.a. microsporocytes
continue to enlarge
undergo meiosis
each producing four microspores
tapetum
neighboring anther cells
act as nurse cells
contributing to microspore development/maturation
initially remain in tetrad
later seperate
expand to characteristic shape
form resistant wall
now called pollen
constitute gynoecium
collective of parts that produce ovule
located highest level of receptacle
three main parts:
1) stigma
catches pollen grains
2) style
elevates stigma to useful position
3) ovary
where megaspores are produced
too few or zero carpels=imperfect flowers
too many carpels (fused)=pistil
placentae (singular, placenta)
tissue that bear ovules
ovules have short stalk=funiculus
carries water/ nutrients
from placenta to ovule
nucellus
central parenchyma
integuments
two thin sheets of cells
surround the nuclellus
leaving small hole (micropyle)
megaspore mother cells
a.k.a. megasporocytes
usually only one enlarges
preparing for meiosis
after meiosis
3/4 megaspores degenerate
only 1 survives
obsorbing protoplasm of other 3
megaspore remains enclosed inside carpel
after egg is fertilized
develops into a seed
develops into the fruit
microspores develop into microgametophytes
megaspores develop into megagametophytes
small/ simple
consists at most 3 cells
within pollen cell wall
microspore nucleus migrates
lies next to the wall
divides mitotically
producing large vegetative cell
small lens-shaped generative cell
divides forming two sperm cells
which germinate producing a pollen tube
penetrates the stigma
embryo sac
multinucleated megagametophyte
nuclei migrate through cytoplasm
until 3 nuclei lie at each end
two are in the center
walls then form around nuclei
8 nucleate megaspore becomes megagametophyte
only 7 cells
1 cell binucleate
7 cells are one large central cell
two polar nuclei
3 antipodal cells
egg apparatus
two synergids
and an egg (the megagametophyte)
Fertilization (syngamy)
plasmogamy
fusion of protoplasts of the gametes
karyogamy
fusion of the nuclei
pollen tube grows downward
through style toward ovule
guided to ovule's micropyle
penetrates nucellus
reaches egg
pollen tube tip bursts
two sperm released
1 sperm nucleus fuses with egg nucleus
diploid zygote
endosperm nucleus
2nd sperm undergoes karyogamy w/central cell
two polar nuclei + sperm nuclei=triploid
three full sets of genes
double fertilization
both sperm nuclei undergo fusions
endosperm
coencytic and cellular tissue
Embryo and Seed Development
endosperm nucleus proliferates
zygote also begins to grow
by both nuclear and cellular divisions
small cluster of cells
embryo proper
suspensor
pushes embryo deep into endosperm
delicate
ephemeral (lasting for a short time)
crushed by later growth of embryo
continue to divide mitotically
developing into embryo
first arranged in small sphere (globular stage)
two primordia grow into cotyledons
cotyledons primordia
give embryo a heart shape (heart stage)
monocots=only 1 primorida grows out
dicotyledon=2 primordia grow out
embryo becomes elongate cyclinder (torpedo stage)
short axis established
radicle (embryonic root)
epicotyl (embryonic stem)
hypocotyl (root/shoot junction)
vascular tissue differentiates
in embryo
albuminous seed=endosperm abundant in mature seed
exalbuminous=endosperm sparse/absent at maturity
integuments that surround nucellus
mature into seed coat (testa)
Fruit Development
ovary matures into fruit
3 distinct layers during growth:
exocarp=outer layer (skin/peel)
mesocarp=middle layer (flesh)
endocarp=innermost layer (pit)
pericarp
entire fruit wall
Flower Structure and Cross-Pollination
Cross-Pollination
pollination of a carpel
by pollen from a different individual
Self-Pollination
pollination of a carpel
by pollen from
same flower
or another flower from same plant
Stamen and Style Maturation Times
self -fertilization prevented if:
anthers stigmas mature at different times
Stigma and Pollen Incompatibility
compatibility barriers
chemical reactions between pollen and carpels
prevent pollen growth
if incompatability proteins match
stigma and style block growth of pollen
Monoecious and Dioecious Species
stamens & carpels (essential organs)
produce critically important spores
imperfect flowers
lack either or both essential organs
perfect flower
has both essential organs
nonessential organs
sepals or petals
dioecy
(dioecious)species with individuals
produce only staminate flowers
produce carpellate flowers
monoecy
staminate flowers and carpellate flowers
located on same plant
monoecious species
extreme adaptation
ensures cross-pollination
Animal-Pollinated Flowers
adaptive mutations resulting in:
pigments
fragrances
sugar-rich secretions
probability of pollination improved
insect-flower association
120 million years ago
coevolution between insects and plants
actinomorphic
radially symmetrical
zygomorphic
billaterally symmetrical
Wind-Pollinated Flowers
adaptive mutations:
prevention of petal formation (energy saved)
reduced or absent sepals
ovaries need no special protection
large feathery stigmas (large number of pollen)
individuals producing thousands of small flowers
Ovary Position
ovary and ovules
must be protected from pollinators
adaptations that maximize seperation
long styles and stamen filaments
ovaries deep within flower
inferior ovary or other parts epigynous
base of stamens, petals, and sepals fuse
creating thick layer of protective tissues around ovaries
superior ovary or hypogynous parts
partially buried ovaries
half-inferior with perigynous flower parts
Inflorescences and Pollination
positoning of flowers important
position of flower relative to other flowers, leaves, and trunk
height from ground
open, uncluttered pollinator flight path
inflorescense
collective visual signal to pollinators
if many flowers are grouped together
two basic arrangements:
1) determinate inflorescences
2) indeterminate inflorescences
Fruit Types and Seed Dispersal
fruits are adaptations
protection
distribution of seeds
gravity
wind
water
animals
True Fruits and Accessory Fruits
"pericarp"
tissues of the fruit
regardless of origin
true fruit
fruits with only ovarian tissue
accessory fruit (or false fruit)
if any nonovarian tissue is present
simple fruit
fruit from single ovary or fused ovaries from one flower
aggregate fruit
separate carpels of one gynoecium fuse
multiple fruit
all individual fruits of an inflorescence fuse into one fruit
Classification of Fruit Types
several ways of grouping (classifying) fruits
dry
fleshy
typically not eaten by
natural seed-distributing animals
eaten
dehiscent fruits
break open
release seeds
indehiscent fruits
do not break open to release seeds