Seed Formation in Gymnosperms & Angiosperms. Fig. 30-2a Gametophyte Sporophyte (2n) Gametophyte (n) Sporophyte Example Dominant Reduced, dependent on

Seed Formation in Gymnosperms & Angiosperms

Fig. 30-2a

Gametophyte

Sporophyte(2n)

Gametophyte(n)

Sporophyte

Example

Dominant

Reduced, dependent ongametophyte for nutrition

Mosses and othernonvascular plants

Fig. 30-2b

Reduced, independent(photosynthetic andfree-living)

Sporophyte(2n)

Gametophyte(n)

Dominant

Ferns and other seedlessvascular plants

Example

Gametophyte

Sporophyte

Fig. 30-2c

Reduced (usually microscopic), dependent on surroundingsporophyte tissue for nutrition

Dominant

Seed plants (gymnosperms and angiosperms)

Gymnosperm AngiospermMicroscopic femalegametophytes (n) inside ovulate cone

Microscopic malegametophytes (n) inside pollencone

Sporophyte (2n) Sporophyte (2n)

Microscopic femalegametophytes (n) insidethese partsof flowers

Microscopic malegametophytes (n) insidethese partsof flowers

Example

Gametophyte

Sporophyte

Fig. 30-2

Reduced (usually microscopic), dependent on surroundingsporophyte tissue for nutrition

Reduced, independent(photosynthetic andfree-living)

Gametophyte

Sporophyte(2n)

Sporophyte(2n)

Gametophyte(n)

Sporophyte

Example

Gametophyte(n)

Dominant

Dominant DominantReduced, dependent ongametophyte for nutrition

Mosses and othernonvascular plants

Ferns and other seedlessvascular plants

Seed plants (gymnosperms and angiosperms)

PLANT GROUP

Gymnosperm Angiosperm

Microscopic femalegametophytes (n) insideovulate cone

Microscopic malegametophytes (n) inside pollencone

Sporophyte (2n) Sporophyte (2n)

Microscopic femalegametophytes (n) insidethese partsof flowers

Microscopic malegametophytes (n) insidethese partsof flowers

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

Microsporangium (2n)

Microsporocytes(2n)

Pollengrains (n)

Pollencone

Microsporangia

MEIOSIS

Maturesporophyte(2n)

Haploid (n)Diploid (2n)

Key

Fig. 30-6-2


Microsporocytes(2n)

Pollengrains (n)

Pollencone

Microsporangia

MEIOSIS



Key

MEIOSIS

Survivingmegaspore (n)

Pollengrain

Megasporangium(2n)

Megasporocyte (2n)

Ovule

Integument

Ovulatecone

Fig. 30-6-3


Microsporocytes(2n)

Pollengrains (n)

Pollencone

Microsporangia

MEIOSIS



Key

MEIOSIS

Pollengrain

Megasporocyte (2n)

Ovule

Integument

Ovulatecone

FERTILIZATION

Pollentube

Femalegametophyte

Spermnucleus (n)

Egg nucleus (n)

Archegonium

Megasporangium(2n)

Fig. 30-6-4


Microsporocytes(2n)

Pollengrains (n)

Pollencone

Microsporangia

MEIOSIS



Key

MEIOSIS

Survivingmegaspore (n)

Pollengrain

Megasporocyte (2n)

Ovule

Integument

Ovulatecone

FERTILIZATION

Pollentube

Femalegametophyte

Spermnucleus (n)

Egg nucleus (n)

Archegonium

Seedling

Seeds

Seed coat(2n)

Foodreserves(n)

Embryo(2n)

Megasporangium(2n)

Fig. 30-3-3

Seed coat(derived fromintegument)

(c) Gymnosperm seed

Embryo (2n)(new sporophyte)

Food supply(femalegametophyte tissue)

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 wind-pollinated

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

Carpel

Ovule

Sepal

Petal

Stigma

Style

Ovary

Stamen Anther

Filament

(or Pistil)(Male)

(Female)

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)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 DevelopmentAnimation: Fruit Development

Fig. 30-8

Hazelnut

Ruby grapefruit

Tomato

Nectarine

Milkweed

Various fruit adaptations help disperse seeds

Seeds can be carried by wind, water, or animals to new locations

Fig. 30-9

Barbs

Seeds within berries

Wings

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 cross-pollination between flowers from different plants of the same species

• 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

The Angiosperm Life Cycle (cont)

Fig. 30-10-1

MEIOSIS

Key

MicrosporangiumMicrosporocytes (2n)

Generative cell

Anther

Tube cell

Pollengrains

Microspore(n)

Male gametophyte(in pollen grain)(n)

Mature flower onsporophyte plant(2n)


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.

http

://b

io.r

utge

rs.e

du/~

gb1

01/la

b8_a

ngi

o_re

pro

/8a3

m-m

icro

gpyt

.htm

l

Fig. 30-10-2

MEIOSIS

Key


Generative cell

Anther

Tube cell

Pollengrains

Microspore(n)




MEIOSIS

Ovule (2n)

Ovary

Megasporangium(2n)

Megaspore(n)

Female gametophyte(embryo sac)

Antipodal cells

Central cell (or polar bodies that form endosperm)

Synergids

Egg (n)

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

http

://b

io.r

utge

rs.e

du/~

gb1

01/la

b8_a

ngi

o_re

pro

/8a3

m-m

icro

gpyt

.htm

l

Fig. 30-10-3

MEIOSIS

Key


Generative cell

Anther

Tube cell

Pollengrains

Microspore(n)




MEIOSIS

Ovule (2n)

Ovary

Megasporangium(2n)

Megaspore(n)


Antipodal cells

Central cell

Synergids

Egg (n)

Pollentube

Pollentube

Stigma

Sperm(n)

Discharged sperm nuclei (n)

FERTILIZATION

Eggnucleus (n)

Style

Sperm

Fig. 30-10-4

MEIOSIS

Key


Generative cell

Anther

Tube cell

Pollengrains

Microspore(n)




MEIOSIS

Ovule (2n)

Ovary

Megasporangium(2n)

Megaspore(n)


Antipodal cells

Central cell

Synergids

Egg (n)

Pollentube

Pollentube

Stigma

Sperm(n)

Discharged sperm nuclei (n)

FERTILIZATION

Germinatingseed

Embryo (2n)Endosperm (3n)Seed coat (2n)

Seed

Nucleus ofdevelopingendosperm(3n)

Zygote (2n)Eggnucleus (n)

Style

Sperm

Practice!!!

http://bio.rutgers.edu/~gb101/lab8_angio_repro/index.html

Documents

Seed Formation in Gymnosperms & Angiosperms. Fig. 30-2a Gametophyte Sporophyte (2n) Gametophyte (n) Sporophyte Example Dominant Reduced, dependent on