Seed Formation in
Gymnosperms & Angiosperms
Fig. 30-2a
Mosses and other
nonvascular plants
Gametophyte Dominant
Sporophyte
Reduced, dependent on
gametophyte for nutrition
Sporophyte
(2n)
Gametophyte
(n)
Example
Fig. 30-2b
Ferns and other seedless
vascular plants
Reduced, independent
Gametophyte (photosynthetic and
free-living)
Sporophyte
Dominant
Sporophyte
(2n)
Example
Gametophyte
(n)
Fig. 30-2c
Seed plants (gymnosperms and angiosperms)
Reduced (usually microscopic), dependent on surrounding
Gametophyte sporophyte tissue for nutrition
Sporophyte Dominant
Gymnosperm
Microscopic female
gametophytes (n)
inside ovulate cone
Angiosperm
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Example
Microscopic male
gametophytes (n)
inside pollen
cone
Sporophyte (2n)
Sporophyte (2n)
Microscopic
female
gametophytes
(n) inside
these parts
of flowers
Fig. 30-2
PLANT GROUP
Mosses and other
nonvascular plants
Gametophyte Dominant
Sporophyte
Ferns and other seedless
vascular plants
Seed plants (gymnosperms and angiosperms)
Reduced, independent
(photosynthetic and
free-living)
Reduced (usually microscopic), dependent on surrounding
sporophyte tissue for nutrition
Reduced, dependent on
Dominant
gametophyte for nutrition
Dominant
Gymnosperm
Sporophyte
(2n)
Microscopic female
gametophytes (n) inside
ovulate cone
Sporophyte
(2n)
Gametophyte
(n)
Angiosperm
Microscopic
female
gametophytes
(n) inside
these parts
of flowers
Example
Microscopic male
gametophytes (n)
inside pollen
cone
Sporophyte (2n)
Gametophyte
(n)
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Sporophyte (2n)
Pollen and Production of Sperm

Microspores develop into pollen grains, which
contain the male gametophytes

Pollination is the transfer of pollen to the part
of a seed plant containing the ovules
Pollen eliminates the need for a film of water
and can be dispersed great distances by air or
animals
If a pollen grain germinates, it gives rise to a
pollen tube that discharges two sperm into the
female gametophyte within the ovule


The Evolutionary Advantage of Seeds


A seed is a sporophyte embryo, along with its
food supply, packaged in a protective coat
Seeds provide some evolutionary advantages
over spores:
–
–
They may remain dormant for days to years, until
conditions are favorable for germination
They may be transported long distances by wind or
animals
Fig. 30-6-1
Key
Haploid (n)
Diploid (2n)
Pollen
cone
Mature
sporophyte
(2n)
Microsporocytes
(2n)
Pollen
grains (n)
MEIOSIS
Microsporangia
Microsporangium (2n)
Fig. 30-6-2
Key
Haploid (n)
Diploid (2n)
Ovule
Ovulate
cone
Pollen
cone
Mature
sporophyte
(2n)
Megasporocyte (2n)
Integument
Microsporocytes
(2n)
Megasporangium
Pollen (2n)
Pollen grain
grains (n) MEIOSIS
MEIOSIS
Microsporangia
Microsporangium (2n)
Surviving
megaspore (n)
Fig. 30-6-3
Key
Haploid (n)
Diploid (2n)
Ovule
Ovulate
cone
Pollen
cone
Mature
sporophyte
(2n)
Megasporocyte (2n)
Integument
Microsporocytes
(2n)
Megasporangium
Pollen (2n)
Pollen grain
grains (n) MEIOSIS
MEIOSIS
Microsporangia
Microsporangium (2n)
Archegonium
Female
gametophyte
Sperm
nucleus (n)
Pollen
tube
FERTILIZATION
Egg nucleus (n)
Fig. 30-6-4
Key
Haploid (n)
Diploid (2n)
Ovule
Ovulate
cone
Pollen
cone
Megasporocyte (2n)
Integument
Microsporocytes
(2n)
Megasporangium
Pollen (2n)
Pollen grain
grains (n) MEIOSIS
MEIOSIS
Mature
sporophyte
(2n)
Microsporangia
Microsporangium (2n)
Seedling
Archegonium
Female
gametophyte
Seeds
Food
reserves
(n)
Seed coat
(2n)
Embryo
(2n)
Sperm
nucleus (n)
Pollen
tube
FERTILIZATION
Egg nucleus (n)
Surviving
megaspore (n)
Fig. 30-3-3
Seed coat
(derived from
integument)
Food supply
(female
gametophyte tissue)
Embryo (2n)
(new sporophyte)
(c) Gymnosperm seed
Angiosperms


Angiosperms are seed plants with
reproductive structures called flowers and
fruits
They are the most widespread and diverse
of all plants
Flowers


The flower is an angiosperm structure
specialized for sexual reproduction
Many species are pollinated by insects or
animals, while some species are windpollinated

A flower is a specialized shoot with up to
four types of modified leaves:
–
–
–
–
Sepals, which enclose the flower
Petals, which are brightly colored and attract
pollinators
Stamens, which produce pollen on their terminal
anthers
Carpels, which produce ovules
Fig. 30-7
(Female)
(Male)
Stamen
Stigma
Anther
Carpel
Style
Filament
Ovary
Petal
Sepal
Ovule
(or Pistil)

A carpel (or pistil) consists of an ovary
at the base and a style leading up to a
stigma, where pollen is received
Video: Flower Blooming (time lapse)
Fruits



A fruit typically consists of a mature ovary
but can also include other flower parts
Fruits protect seeds and aid in their
dispersal
Mature fruits can be either fleshy or dry
Animation: Fruit Development
Fig. 30-8
Tomato
Ruby grapefruit
Nectarine
Hazelnut
Milkweed


Various fruit adaptations help disperse
seeds
Seeds can be carried by wind, water, or
animals to new locations
Fig. 30-9
Wings
Seeds within berries
Barbs
The Angiosperm Life Cycle
•
The flower of the sporophyte is composed of both
male and female structures
•
Male gametophytes are contained within pollen
grains produced by the microsporangia of anthers
•
The female gametophyte, or embryo sac, develops
within an ovule contained within an ovary at the
base of a stigma
•
Most flowers have mechanisms to ensure crosspollination between flowers from different plants of
the same species
The Angiosperm Life Cycle (cont)
•
•
•
A pollen grain that has landed on a stigma
germinates and the pollen tube of the male
gametophyte grows down to the ovary
The ovule is entered by a pore called the
micropyle
Double fertilization occurs when the
pollen tube discharges two sperm into the
female gametophyte within an ovule
The Angiosperm Life Cycle (cont)
•
•
•
One sperm fertilizes the egg (now a zygote
(2n)), while the other combines with two nuclei
in the central cell of the female gametophyte
and initiates development of food-storing
endosperm (3n)
The endosperm nourishes the developing
embryo
Within a seed, the embryo consists of a root
and two seed leaves called cotyledons
Fig. 30-10-1
Key
Haploid (n)
Diploid (2n)
Mature flower on
sporophyte plant
(2n)
Anther
Microsporangium
Microsporocytes (2n)
MEIOSIS
Microspore
(n)
Generative cell
Tube cell
Male gametophyte
(in pollen grain)
Pollen
(n)
grains
http://bio.rutgers.edu/~gb101/lab8_angio_repro/8a3m-microgpyt.html
A diploid microsporocyte, or
microspore mother cell, divides to
give rise to four haploid
microspores.
Each microspore
divides by mitosis to
form two haploid
nuclei (the tube
nucleus and the
generative nucleus);
After landing on the
stigma, the pollen
germinates forming a
pollen tube; the
generative nucleus then
divides by mitosis to
form two haploid sperm
nuclei.
Fig. 30-10-2
Key
Haploid (n)
Diploid (2n)
Mature flower on
sporophyte plant
(2n)
Microsporangium
Microsporocytes (2n)
Anther
MEIOSIS
Ovule (2n) Microspore
(n)
Ovary
MEIOSIS
Generative cell
Tube cell
Male gametophyte
(in pollen grain)
Pollen
(n)
grains
Megasporangium
(2n)
Megaspore
(n)
Antipodal cells
Female gametophyte Central cell (or polar bodies that form endosperm)
(embryo sac)
Synergids
Egg (n)
http://bio.rutgers.edu/~gb101/lab8_angio_repro/8a3m-microgpyt.html
A diploid megasporocyte (megaspore
mother cell) undergoes meiosis, giving
rise to four haploid megaspore nuclei (3
of which disintegrate).
The remaining
megaspore nucleus
undergoes three
mitotic divisions to
form eight haploid
nuclei.
Nuclear migration and
cytokinesis occur to form the
mature megagametophyte
Fig. 30-10-3
Key
Haploid (n)
Diploid (2n)
Mature flower on
sporophyte plant
(2n)
Microsporangium
Microsporocytes (2n)
Anther
MEIOSIS
Ovule (2n) Microspore
(n)
Ovary
MEIOSIS
Megasporangium
(2n)
Male gametophyte
(in pollen grain)
Pollen
(n)
grains
Stigma
Pollen
tube
Megaspore
(n)
Antipodal cells
Female gametophyte Central cell
(embryo sac)
Synergids
Egg (n)
Generative cell
Tube cell
Sperm
Style
Pollen
tube
Sperm
(n)
FERTILIZATION
Egg
nucleus (n)
Discharged sperm nuclei (n)
Fig. 30-10-4
Key
Haploid (n)
Diploid (2n)
Mature flower on
sporophyte plant
(2n)
Microsporangium
Microsporocytes (2n)
Anther
MEIOSIS
Ovule (2n) Microspore
(n)
Ovary
Germinating
seed
MEIOSIS
Megasporangium
(2n)
Embryo (2n)
Endosperm (3n)
Seed
Seed coat (2n)
Nucleus of
developing
endosperm
(3n)
Male gametophyte
(in pollen grain)
Pollen
(n)
grains
Stigma
Pollen
tube
Megaspore
(n)
Antipodal cells
Female gametophyte Central cell
(embryo sac)
Synergids
Egg (n)
Generative cell
Tube cell
Sperm
Style
Pollen
tube
Sperm
(n)
FERTILIZATION
Zygote (2n)
Egg
nucleus (n)
Discharged sperm nuclei (n)
Practice!!!

http://bio.rutgers.edu/~gb101/lab8_angio_rep
ro/index.html