Plant Diversity 1 How Plants Colonized Land. From Water to Land In order to survive the transition from water to land, it was necessary for plants to

Plant Diversity 1Plant Diversity 1

How Plants Colonized LandHow Plants Colonized Land

From Water to LandFrom Water to Land

In order to survive the transition from In order to survive the transition from water to land, it was necessary for plants water to land, it was necessary for plants to make adaptations for obtaining water to make adaptations for obtaining water and to prevent them from drying out. and to prevent them from drying out.

Reproduction in Water Reproduction in Water PlantsPlants

Algae reproduce with flagellated sperm Algae reproduce with flagellated sperm cells which require water for fertilization. cells which require water for fertilization.

Land plants must be able to reproduce Land plants must be able to reproduce without water. without water.

Surviving UV radiationSurviving UV radiation

Once plants emerge from the protective Once plants emerge from the protective cover of water, the genetic material cover of water, the genetic material (DNA) is more susceptible to damage by (DNA) is more susceptible to damage by ultraviolet radiation. ultraviolet radiation.

Major Plant Adaptations Major Plant Adaptations for Survival on Land:for Survival on Land:

1. Except for primitive bryophytes, the 1. Except for primitive bryophytes, the dominant generation of all plants is the diploid dominant generation of all plants is the diploid sporophyte generation. sporophyte generation.

A diploid structure is more apt to survive A diploid structure is more apt to survive genetic damage because two copies of each genetic damage because two copies of each chromosome allows recessive mutations to be chromosome allows recessive mutations to be masked.masked.


2. All plants possess a cuticle, a waxy 2. All plants possess a cuticle, a waxy covering on aerial parts that reduces covering on aerial parts that reduces desiccation (drying out). desiccation (drying out).


3. The development of a vascular system 3. The development of a vascular system in plants further reduced their dependency in plants further reduced their dependency on water. on water.

Without a vascular system, all cells must Without a vascular system, all cells must be reasonably close to water. be reasonably close to water.

A vascular system allowsA vascular system allows

for water to be distributedfor water to be distributed

throughout the plant. throughout the plant.


4. In the more primitive plants, flagellated 4. In the more primitive plants, flagellated sperm require water to swim to the eggs.sperm require water to swim to the eggs.

In the more advanced plants, the sperm, In the more advanced plants, the sperm, packaged as pollen, are adapted for packaged as pollen, are adapted for delivery by wind or animals. delivery by wind or animals.


5. In the most advanced division of 5. In the most advanced division of plants, the Anthophyta*, the plants, the Anthophyta*, the gametophytes are enclosed (and thus gametophytes are enclosed (and thus protected) inside an ovary. protected) inside an ovary.

*These are the flowering*These are the flowering

plants. plants.


6. The most advanced plants (Conifers 6. The most advanced plants (Conifers and Flowering plants) have developed and Flowering plants) have developed adaptations to seasonal variations in the adaptations to seasonal variations in the availability of water and light. Ex: availability of water and light. Ex:

Deciduous Trees shed their leaves to minimize water loss during the dormant season.

Desert wildflowers germinate, grow, bloom and produce seeds during the brief time there is water after a rain.

Key Idea! Key Idea!

Understand how the various plant types Understand how the various plant types evolved:evolved:

Chlorophytes Chlorophytes → Bryophytes → → Bryophytes →

Seedless Vascular Plants → Seedless Vascular Plants → Gymnosperms → AngiospermsGymnosperms → Angiosperms

Chlorophyta—Green Chlorophyta—Green AlgaeAlgae

Scientists have found enough evidence to conclude Scientists have found enough evidence to conclude that they are the common ancestors of land plants.that they are the common ancestors of land plants.

They have both chlorophyll They have both chlorophyll a a and and bb.. They have cellulose cell walls and store their They have cellulose cell walls and store their

carbohydrates as starch.carbohydrates as starch. Some species show trends towards multicellular Some species show trends towards multicellular

colonies.colonies.

CosmariumDesmidium

Microasterius

Volvox colony

BryophytesBryophytes

Bryophytes are Bryophytes are considered the most considered the most primitive land plants.primitive land plants.

They were the first to They were the first to evolve from the evolve from the chlorophytes.chlorophytes.

They include They include mosses, liverworts, mosses, liverworts, and hornworts.and hornworts.

Bryophytes’ Evolution Bryophytes’ Evolution from Water:from Water:

In order to survive on In order to survive on land where water is not land where water is not unlimited, two unlimited, two evolutionary adaptations evolutionary adaptations helped:helped:

1) A waxy cuticle to 1) A waxy cuticle to protect against water protect against water lossloss

2) the packaging of 2) the packaging of gametes in structures gametes in structures known as gametangia. known as gametangia.

The gametangia provide a safe haven because the fertilization and development of the zygote occur within the protected structure.

Alternation of Alternation of Generations in Plants:Generations in Plants:

In plants, a multicellular sporophyte (diploid, 2N) In plants, a multicellular sporophyte (diploid, 2N) alternates with a multicellular gametophyte (haploid, 1N)alternates with a multicellular gametophyte (haploid, 1N)

In plants, meiosis produces spores. Spores are haploid cells that divide by mitosis to become a multicellular haploid organism, the gametophyte. Gametes are produced by the gametophyte by mitosis since it is already haploid.

Alternation of Alternation of Generations in Plants:Generations in Plants:

When both the gametophyte and sporophyte When both the gametophyte and sporophyte stages are multicellular, the life cycle stages are multicellular, the life cycle demonstrates an alternation of generations. demonstrates an alternation of generations.

The gametes fuse and produce a diploid cell that grows by mitosis to become the sporophyte. Specialized cells in the sporophyte divide by meiosis to produce spores.

Bryophyte ReproductionBryophyte Reproduction

In bryophytes, the gametes are packaged in In bryophytes, the gametes are packaged in structures called structures called gametangia.gametangia.

Bryophyte sperm is produced by the male Bryophyte sperm is produced by the male gametangia, called gametangia, called antheridiaantheridia..

Bryophyte eggs are produced by the female Bryophyte eggs are produced by the female gametangia, called gametangia, called archegoniumarchegonium. .

The gametangia provide a safe haven because The gametangia provide a safe haven because the fertilization and development of the zygote the fertilization and development of the zygote occur within the protected structure. occur within the protected structure.

LiverwortsLiverworts

Liverworts are very small Liverworts are very small plants (usually less than plants (usually less than 1” in size)1” in size)

Like all Bryophytes, they Like all Bryophytes, they live in very moist places live in very moist places since they reproduce since they reproduce with flagellated sperm with flagellated sperm that must swim through that must swim through water to fertilize the water to fertilize the eggs. eggs.

LiverwortsLiverworts

Like other bryophytes, liverworts Like other bryophytes, liverworts do not have vascular tissues to do not have vascular tissues to carry water. carry water.

This lack of vascular tissue (plus This lack of vascular tissue (plus the fact they have flagellated the fact they have flagellated sperm cells) results in a sperm cells) results in a dependence on water. dependence on water.

For this reason, bryophytes must For this reason, bryophytes must live in damp areas so they don’t live in damp areas so they don’t dry out. dry out.

HornwortsHornworts

Reproductive structures at the tips release spores

HornwortsHornworts

The group's common The group's common name "hornwort" name "hornwort" refers to the tall refers to the tall narrow narrow sporophytessporophytes which are embedded which are embedded in the top of the in the top of the plant.plant.

MossesMosses

Mosses are special Mosses are special because, unlike in all because, unlike in all other plants, the other plants, the dominant generation dominant generation in their life cycle is the in their life cycle is the haploid gameophyte. haploid gameophyte. (What you see when (What you see when you look at a moss you look at a moss plant is a collection of plant is a collection of haploid cells!) haploid cells!)

MossesMosses

The moss sporophyte (2N) is tiny, short-The moss sporophyte (2N) is tiny, short-lived, and relies on the gametophyte (1N) lived, and relies on the gametophyte (1N) for nutritional support. for nutritional support.

Tracheophytes—The First Tracheophytes—The First Vascular Plants Vascular Plants

The transition from The transition from water to land was water to land was tricky—how to get tricky—how to get nutrients and water nutrients and water from the soil up to all from the soil up to all parts of the plant?parts of the plant?

The answer: Phloem The answer: Phloem and Xylem—Vascular and Xylem—Vascular tissues that transport tissues that transport materials.materials.

Vascular PlantsVascular Plants

Xylem—water Xylem—water superhighway, superhighway, transporting water transporting water from the soil from the soil throughout all parts of throughout all parts of the plantthe plant

Phloem—Sugar food Phloem—Sugar food superhighway, superhighway, transporting sugar transporting sugar and nutrients. and nutrients.

Tracheophytes—First Tracheophytes—First Vascular PlantsVascular Plants

The first vascular The first vascular plants to evolve did plants to evolve did not have seeds.not have seeds.

They live their lives as They live their lives as sporophytes (2N).sporophytes (2N).

They produce spores They produce spores (haploid) which are (haploid) which are bisexual (neither male bisexual (neither male nor female)nor female)

Ferns-Spores on LeavesFerns-Spores on Leaves

The spores of ferns live on the underside The spores of ferns live on the underside of the leaves. The spores will germinate of the leaves. The spores will germinate to form tiny gametophytes under the leaf to form tiny gametophytes under the leaf surface. surface.

Fern Life CycleFern Life Cycle

http://academic.kellogg.edu/herbrandsonc/bio111/animations/0124.swf

Seed PlantsSeed Plants

Seeds are packages containing an Seeds are packages containing an embryo and the food to feed the embryo and the food to feed the developing embryo that is surrounded by developing embryo that is surrounded by a nice protective shell. a nice protective shell.

Evolution of Seed PlantsEvolution of Seed Plants

3 major changes led to the evolution of seed 3 major changes led to the evolution of seed plants:plants:

1. Further decline in the prominence of the 1. Further decline in the prominence of the gametophyte generation of the life cycle.gametophyte generation of the life cycle.

2. The birth of pollination2. The birth of pollination 3. The evolution of the seed.3. The evolution of the seed.

GymnospermsGymnosperms

The first major seed plants to surface The first major seed plants to surface were the gymnosperms (“naked” “seeds”)were the gymnosperms (“naked” “seeds”)

The most important gymnosperms are the Conifers. Their reproductive structures are cones.They include pine trees, firs, cedars and redwoods.

GymnospermsGymnosperms

Gymnosperms produce both male and female gametes. Gymnosperms transport their sperm through the use of pollen. These plants survive well in dry conditions and keep their leaves all year.They usually have needles for leaves.

PollenPollen

Pollen is the sperm-bearing male gametophyte Pollen is the sperm-bearing male gametophyte (1N).(1N).

Pollen grains have a hard coat that protects the Pollen grains have a hard coat that protects the sperm cells during the process of their sperm cells during the process of their movement from the stamens to the pistil of movement from the stamens to the pistil of flowering plants or from the male cone to the flowering plants or from the male cone to the female cone of conifers.female cone of conifers.

Gymnosperms Life CycleGymnosperms Life Cycle

Flowering PlantsFlowering Plants

The final major plant evolutionary The final major plant evolutionary category to branch off are the flowering category to branch off are the flowering plants.plants.

Today, there are more of these than any Today, there are more of these than any other plants. other plants.

AngiospermsAngiosperms

Flowers are the Flowers are the reproductive reproductive structures of the structures of the angiosperms angiosperms (“covered” “seeds”)(“covered” “seeds”)

AngiospermsAngiosperms

The flower is a major evolutionary advancement The flower is a major evolutionary advancement because:because:

It attracts pollinators such as insects and birdsIt attracts pollinators such as insects and birds The ovules are protected inside the ovaryThe ovules are protected inside the ovary The ovary develops into The ovary develops into

a fruit which fosters the a fruit which fosters the

dispersal of seeds by wind,dispersal of seeds by wind,

insects, birds, mammals andinsects, birds, mammals and

other animals. other animals.

Angiosperm Life CycleAngiosperm Life Cycle

Major Evolutionary Major Evolutionary Trends in the Plant Trends in the Plant Kingdom:Kingdom:

Dominant gametophyte generation Dominant gametophyte generation → → dominant sporophyte generationdominant sporophyte generation

Nonvascular → vascularNonvascular → vascular Seedless → seedsSeedless → seeds Motile sperm → pollenMotile sperm → pollen Naked seeds → seeds in flowersNaked seeds → seeds in flowers

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Plant Diversity 1 How Plants Colonized Land. From Water to Land In order to survive the transition from water to land, it was necessary for plants to