Презентация на тему Plant Diversity II: The Evolution of Seed Plants

Презентация на тему Plant Diversity II: The Evolution of Seed Plants, предмет презентации: Биология. Этот материал содержит 47 слайдов. Красочные слайды и илюстрации помогут Вам заинтересовать свою аудиторию. Для просмотра воспользуйтесь проигрывателем, если материал оказался полезным для Вас - поделитесь им с друзьями с помощью социальных кнопок и добавьте наш сайт презентаций ThePresentation.ru в закладки!

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Слайд 1
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Chapter 30

Plant Diversity II: The Evolution of Seed Plants


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Overview: Transforming the World

Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems.
A seed consists of an embryo and nutrients surrounded by a protective coat.
The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte.


Слайд 3
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What human reproductive organ is functionally similar to this seed?


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Seeds and pollen grains are key adaptations for life on land

In addition to seeds, the following are common to all seed plants:
Reduced gametophytes
Heterospory
Ovules
Pollen


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Gametophyte / sporophyte relationships in different plant groups

Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition

Reduced, independent (photosynthetic and free-living)

Gametophyte

Sporophyte (2n)

Sporophyte (2n)

Gametophyte (n)

Sporophyte

Example

Gametophyte (n)

Dominant

Dominant

Dominant

Reduced, dependent on gametophyte for nutrition

Mosses and other nonvascular plants

Ferns and other seedless vascular plants

Seed plants (gymnosperms and angiosperms)

PLANT GROUP

Gymnosperm

Angiosperm

Microscopic female gametophytes (n) inside ovulate cone

Microscopic male gametophytes (n) inside pollen cone

Sporophyte (2n)

Sporophyte (2n)

Microscopic female gametophytes (n) inside these parts of flowers

Microscopic male gametophytes (n) inside these parts of flowers


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Heterospory: The Rule Among Seed Plants

The ancestors of seed plants were likely homosporous, while seed plants are heterosporous.
Megasporangia produce megaspores that give rise to female gametophytes.
Microsporangia produce microspores that give rise to male gametophytes.


Слайд 7
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Ovules and Production of Eggs

An ovule consists of a megasporangium, megaspore, and one or more protective integuments.
A fertilized ovule becomes a seed.
Gymnosperm megaspores have one integument.
Angiosperm megaspores usually have two integuments.


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From ovule to seed in a gymnosperm

Megasporangium (2n)

Megaspore (n)

(a) Unfertilized ovule

Integument

Spore wall

Immature female cone


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Pollen and Production of Sperm

Microspores develop into pollen grains, which contain the male gametophytes.
Pollination is the transfer of pollen from the male to the female part 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.


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From ovule to seed in a gymnosperm

Male gametophyte (within a germinated pollen grain) (n)

Female gametophyte (n)

(b) Fertilized ovule

Micropyle

Pollen grain (n)

Spore wall

Discharged sperm nucleus (n)

Egg nucleus (n)


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The Evolutionary Advantage of Seeds

A seed develops from the whole ovule.
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.


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From ovule to seed in a gymnosperm

Seed coat (derived from integument)

(c) Gymnosperm seed

Embryo (2n) (new sporophyte)

Food supply (female gametophyte tissue) (n)


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From ovule to seed in a gymnosperm

Seed coat (derived from integument)

(c) Gymnosperm seed

Embryo (2n) (new sporophyte)

Food supply (female gametophyte tissue) (n)

(b) Fertilized ovule

(a) Unfertilized ovule

Integument

Immature female cone

Spore wall

Megasporangium (2n)

Male gametophyte (within a germinated pollen grain) (n)

Megaspore (n)

Micropyle

Pollen grain (n)

Egg nucleus (n)

Discharged sperm nucleus (n)

Female gametophyte (n)


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Gymnosperms bear “naked” seeds, typically on cones

The gymnosperms have “naked” seeds not enclosed by ovaries and exposed on modified leaves - cones. There are four phyla:
Cycadophyta (cycads)
Gingkophyta (one living species: Ginkgo biloba)
Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia)
Coniferophyta (conifers, such as pine, fir, and redwood).


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Seed plants can be divided into two clades: gymnosperms and angiosperms.
Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems.
Gymnosperms were better suited than nonvascular plants to drier conditions.
Today, cone-bearing gymnosperms called conifers dominate in the northern latitudes.


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Phylum Ginkgophyta

This phylum consists of a single living species, Ginkgo biloba.
It has a high tolerance to air pollution and is a popular ornamental tree.


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Gymnosperm

Ginkgo biloba Pollen-producing tree with fleshy seeds


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Gymnosperm

Welwitschia

Ovulate cones


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Phylum Coniferophyta

This phylum is by far the largest of the gymnosperm phyla.
Most conifers are evergreens and can carry out photosynthesis year round.


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Gymnosperms: Conifers perform year round photosynthesis

Douglas fir


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Gymnosperms: Conifers Sequoia - One of the Largest and Oldest Living Organisms

Giant Sequoia: 2,500 tons / 1,800 - 2,700 years old


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The Life Cycle of a Pine: A Closer Look

Three key features of the gymnosperm life cycle are:
Dominance of the sporophyte generation.
The transfer of sperm to ovules by pollen.
Development of seeds from fertilized ovules.

The life cycle of a pine provides an example.



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Life Cycle of a Pine

Microsporangium (2n)

Microsporocytes (2n)

Pollen grains (n)

Pollen cone

Microsporangia

MEIOSIS

Mature sporophyte (2n)

Haploid (n)

Diploid (2n)

Key

MEIOSIS

Surviving megaspore (n)

Pollen grain

Megasporocyte (2n)

Ovule

Integument

Ovulate cone

FERTILIZATION

Pollen tube

Female gametophyte

Sperm nucleus (n)

Egg nucleus (n)

Archegonium

Seedling

Seeds

Seed coat (2n)

Food reserves (n)

Embryo (2n)

Megasporangium (2n)


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The reproductive adaptations of angiosperms include flowers and fruits

Angiosperms are seed plants with reproductive structures called flowers and fruits.
They are the most widespread and diverse of all plants.
All angiosperms are classified in a single phylum: Anthophyta.
The name comes from the Greek anthos, flower.


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Flowers - Specialized for Sexual Reproduction

The flower is an angiosperm structure specialized for sexual reproduction. It is a specialized shoot with up to four types of modified leaves:
Sepals - enclose the flower
Petals - brightly colored and attract pollinators
Stamens - produce pollen on their terminal anthers
Carpels - consist of an ovary containing ovules at the base and a style holding up a stigma, where pollen is received.



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Structure of an Idealized Flower

Carpel

Ovule

Sepal

Petal

Stigma

Style

Ovary

Stamen

Anther

Filament




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Fruits

A fruit typically consists of a mature ovary but can also include other flower parts.
Fruits protect seeds and aid in seed dispersal.
Mature fruits can be either fleshy or dry.
Various fruit adaptations help disperse seeds by wind, water, or animals to new locations.


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Fruits

Hazelnut

Ruby grapefruit

Tomato

Nectarine

Milkweed







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Fruit Adaptations for Seed Dispersal

Barbs

Seeds within berries

Wings





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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 = 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.


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A pollen grain that has landed on a stigma germinates and the pollen tube of the male gametophyte grows down to the ovary.
Sperm enter the ovule through a pore opening called the micropyle.
Double fertilization occurs when the pollen tube discharges two sperm into the female gametophyte within an ovule.


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One sperm fertilizes the egg forming a zygote.
The other sperm combines with two nuclei and initiates development of food-storing endosperm.
The endosperm nourishes the developing embryo.
Within a seed, the embryo consists of a root and two seed leaves called cotyledons.

Double Fertilization: Produces
Zygote 2n and endosperm (food) 3n


Слайд 33
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Life Cycle of an Angiosperm

MEIOSIS

Key

Microsporangium

Microsporocytes (2n)

Generative cell

Anther

Tube cell

Pollen grains

Microspore (n)

Male gametophyte (in pollen grain) (n)

Mature flower on sporophyte plant (2n)

Haploid (n)

Diploid (2n)

MEIOSIS

Ovule (2n)

Ovary

Megasporangium (2n)

Megaspore (n)

Female gametophyte (embryo sac)

Antipodal cells Central cell Synergids Egg (n)


Pollen tube

Pollen tube

Stigma

Sperm (n)

Discharged sperm nuclei (n)

FERTILIZATION

Germinating seed

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

Seed

Nucleus of developing endosperm (3n)

Zygote (2n)


Egg nucleus (n)

Style

Sperm



Слайд 34
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Angiosperm Phylogeny

The ancestors of angiosperms and gymnosperms diverged about 305 million years ago.
Angiosperms may be closely related to Bennettitales, extinct seed plants with flowerlike structures.
Amborella and water lilies are likely descended from two of the most ancient angiosperm lineages.


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Angiosperm evolutionary history

Microsporangia (contain microspores)

Ovules

A possible ancestor of the angiosperms?

(a)

(b)

Angiosperm phylogeny

Most recent common ancestor of all living angiosperms

Millions of years ago

300 250 200 150 100 50 0

Living gymnosperms

Bennettitales

Amborella

Star anise and relatives

Water lilies

Monocots

Magnoliids

Eudicots


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Angiosperm Diversity

The two main groups of angiosperms are: monocots - one cotyledon eudicots (“true” dicots) - two cotyledons.
More than one-quarter of angiosperm species are monocots.
More than two-thirds of angiosperm species are eudicots.


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Angiosperms: Monocots and Eudicots

Monocot Characteristics

Eudicot Characteristics

Vascular tissue usually arranged in ring

Veins usually parallel

Veins usually netlike

Vascular tissue scattered

Leaf venation

One cotyledon

Embryos

Two cotyledons

Stems

Roots

Pollen

Root system usually fibrous (no main root)

Pollen grain with three openings

Taproot (main root) usually present

Pollen grain with one opening

Floral organs usually in multiples of three

Flowers

Floral organs usually in multiples of four or five


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Evolutionary Links Between Angiosperms and Animals

Pollination of flowers and transport of seeds by animals are two important relationships in terrestrial ecosystems.
Clades with bilaterally symmetrical flowers have more species than those with radially symmetrical flowers.
This is likely because bilateral symmetry affects the movement of pollinators and reduces gene flow in diverging populations.


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Can Flower Shape Influence Speciation Rate?

Common ancestor

Radial symmetry (N = 4)

Bilateral symmetry (N = 15)

Compare numbers of species

Time since divergence from common ancestor

“Radial” clade

“Bilateral” clade

3,000

2,000

1,000

0

EXPERIMENT

RESULTS

Mean difference in number of species


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Human welfare depends greatly on seed plants

No group of plants is more important to human survival than seed plants.
Plants are key sources of food, fuel, wood products, and medicine.
Our reliance on seed plants makes preservation of plant diversity critical.


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Products from Seed Plants

Most of our food comes from angiosperms. Six crops (wheat, rice, maize, potatoes, cassava, and sweet potatoes) yield 80% of the calories consumed by humans.
Modern crops are products of relatively recent genetic change resulting from artificial selection.
Many seed plants provide wood.
Secondary compounds of seed plants are used in medicines.


Слайд 42

Слайд 43
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Threats to Plant Diversity

Destruction of habitat is causing extinction of many plant species.
Loss of plant habitat is often accompanied by loss of the animal species that plants support.
At the current rate of habitat loss, 50% of Earth’s species will become extinct within the next 100–200 years.


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Summary

Reduced gametophytes

Microscopic male and female gametophytes (n) are nourished and
protected by the sporophyte (2n)

Five Derived Traits of Seed Plants

Male gametophyte

Female gametophyte

Heterospory

Microspore (gives rise to a male gametophyte)

Megaspore (gives rise to a female gametophyte)

Ovules

Ovule (gymnosperm)

Pollen

Pollen grains make water unnecessary for fertilization

Integument (2n)

Megaspore (2n)

Megasporangium (2n)



Seeds

Seeds: survive better than unprotected spores, can be transported long distances

Integument

Food supply

Embryo


Слайд 45
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Plant Evolutionary Relationships: Clades

Charophyte green algae

Mosses

Ferns

Gymnosperms

Angiosperms


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You should now be able to:

Explain why pollen grains were an important adaptation for successful reproduction on land.
List the four phyla of gymnosperms.
Describe the life history of a pine; indicate which structures are part of the gametophyte generation and which are part of the sporophyte generation.


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You should now be able to:

Identify and describe the function of the following floral structures: sepals, petals, stamens, carpels, filament, anther, stigma, style, ovary, and ovule.
Explain how fruits may be adapted to disperse seeds.
Diagram the generalized life cycle of an angiosperm; indicate which structures are part of the gametophyte generation and which are part of the sporophyte generation.
Describe the current threat to plant diversity caused by human population growth.



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