Flowers and Reproduction (Angiosperms)

Asexual Reproduction

fragmentation

individual parts become self sufficient

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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

flower 1

flower2

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

endosperm

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)

show4.open_seed

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

botany-anatomy-jan-2012-53-728

Perfect+Flower+Has+both+Pistil+(Female)+and+Stamen+(Male)+Examples_

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

symmetry actin

symmetry

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

wind pollination

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

inflorescence_types1_med

inflorescence_types2_med

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

strawberry

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multiple fruit

all individual fruits of an inflorescence fuse into one fruit

pineapple3

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