How Plants Colonized Onto Land

First Sign of a Plant  The first plant was a form of green algae called Charophyceans.  Molecular homologies present evidence of ancestry to land plants.  Similar chlorophyll pigments  Homologous cell walls  Homologouus peroxisomes  Homologous sperm

CAROPHYCEANS

Necessary Adaptations to Colonize Terrestrial Habitats.  Must be able of protect the gametes.  Dispersal of gametes.  Protection against dehydration.  Vascular system.  Support against gravity.  Development of seeds.

Evolution of Land Plants

Next step up were the Bryophytes  Include mosses, hornworts and liverworts.  Nonvascular plants.  Contain elongated conducting cells that lack liginin that were precursor to a vascular system.  Must have a moist environment to reproduce.  Offspring arise from multicellular embryos that are still attached to the mother plant.  Most predominant form is the gametophyte generation which is haploid.

Meet the Bryophytes

Bryophyte Reproduction  Germinating moss spores develop in a filamentous structure called the protonema.  The large surface area enhances water absorption minerals.  From the protonema emerges the gametophore that produces gametes. This whole structure is known as the gametophyte.  Male gametophyte called the antheridium.  Female gametophyte called the archegonium.  Fertilization produces the sporophyte generation.  Sporophyte grows within the gametophyte giving rise to the sporangium.  Sporanguim produces spores through meiosis.  Spores undergo mitosis and produce the protonema.

The Protonema

Archegonium and Anthridium

Sporophyte Generation

Moss Life Cycle

Bryophytes  Lack true stems and leaves.  Are anchored by long tubular cells called rhizoids.  Have flagellated gametes.

Pteridophytes  Seedless vascular plants.  Ferns, Equisetum (horsetails), Lycophytes (club mosses).  Most have true roots and lignified vascular tissue.  Have small leaves because vascular system is not as developed.  Predominant most visible form is the sporophyte generation.  Most are homosporous. Only aquatic ferns are heterosporous.  The heterosporous condition is very in important in the evolution o seeds.  Gametes are still flagellated so ferns must live in a moist habitat.  Seedless vascular plants formed the “coal forests” of the Carboniferous.

Meet Pteridophyte’s

 Homosporous  Sporophyte produces:  single type of spore bisexaul gametes. That either produce eggs or sperm.  Heterosporous  Sporophyte gives rise to:  Megaspores (female) - egg  Microspore (male) - sperm

Ferns produce clusters of sporangia called sori.

Pteridophyte Reproduction

Carboniferous “coal forests”

THE EVOLUTION OF SEED PLANTS

Seed Plant Evolution Seed plants are vascular plants. Seed plants are vascular plants. Include gymnosperms (conifers) and angiosperms (flowering plants) Include gymnosperms (conifers) and angiosperms (flowering plants) Three primary adaptations: Three primary adaptations: Reduction the gametophyte. Reduction the gametophyte. Advent of the seed. Advent of the seed. Evolution of the seed. Evolution of the seed.

The Sporophyte is the Most Visible Form in seed Plants The gametophyte is contained within the sporangia. The gametophyte is contained within the sporangia. The gametophyte becomes the reproductive tissue of the sporophyte and nourishes the developing embryo. The gametophyte becomes the reproductive tissue of the sporophyte and nourishes the developing embryo. Advantages Advantages Do not have to deal with environmental stresses. Do not have to deal with environmental stresses. Nutrients derived from parent plant. Nutrients derived from parent plant. The female gametophyte and the embryos they produced are sheltered from drought and U.V. radiation. The female gametophyte and the embryos they produced are sheltered from drought and U.V. radiation. Gametophytes in seed plants are microscopic. Gametophytes in seed plants are microscopic.

Seeds are an important means of dispersing offspring. Seeds resist harsh conditions. Seeds resist harsh conditions. Seeds contain the developing embryo and a food supply along with a protective coat. Seeds contain the developing embryo and a food supply along with a protective coat. All seed plants are heterosporous which means they produce two types of sporangia with two types of spores. All seed plants are heterosporous which means they produce two types of sporangia with two types of spores. Megaspore - female spore Megaspore - female spore Microspore - male spore Microspore - male spore

Gymnosperm Seed

Structure of the Seed of Megasporangium Integuments encase and protect the megasporangium with the megaspore inside. Integuments encase and protect the megasporangium with the megaspore inside. The whole structure is known as the ovule. The whole structure is known as the ovule. The megaspore produces one or more eggs and if fertilized will produce the embryo sporophyte. The megaspore produces one or more eggs and if fertilized will produce the embryo sporophyte. Once the seed is released from the parent it remains dormant until there is favorable conditions for the embryo to grow. Once the seed is released from the parent it remains dormant until there is favorable conditions for the embryo to grow.

Structure of Pollen or Microsporangium Microspores develop into pollen which mature into the male gametophyte of seed plants. Microspores develop into pollen which mature into the male gametophyte of seed plants. Transfer of pollen to ovules is called pollination. Transfer of pollen to ovules is called pollination. In most gymnosperms and all angiosperms sperm lack flagella. In most gymnosperms and all angiosperms sperm lack flagella. Transfer can airborne, carried on fur or feathers or “bee fuzz”. Transfer can airborne, carried on fur or feathers or “bee fuzz”. Wider terrestrial range Wider terrestrial range

Gymnosperms Conifers or “naked seed” plants. Conifers or “naked seed” plants. Lack ovaries Lack ovaries Possess pine cones. Possess pine cones. Seeds develop on special leaves called sporophylls. Seeds develop on special leaves called sporophylls. Evolved before angiosperms. Evolved before angiosperms. Reproduction involves: Reproduction involves: Pollen cone (male) Pollen cone (male) Ovulate cone (female) Ovulate cone (female)

Gymnosperm Fertilization Pollen grain is released from microsporangium and reaches the megasporagium in the ovulate cone. Pollen grain is released from microsporangium and reaches the megasporagium in the ovulate cone. Pollen is drawn into ovulate cone through the micropyle and produces a pollen tube. Pollen is drawn into ovulate cone through the micropyle and produces a pollen tube. The megaspore in the megasporangium undergoes meiosis. Same thing happens in the pollen. The megaspore in the megasporangium undergoes meiosis. Same thing happens in the pollen. Fertilization occurs when the sperm nuclei is injected into the egg through the pollen tube. Fertilization occurs when the sperm nuclei is injected into the egg through the pollen tube. More than one egg may be fertilized but only one develops into the zygote. More than one egg may be fertilized but only one develops into the zygote.

Life Cycle of a Pine

Ovulate Cone

Pollen Cone

Pine Embryo

Sequoia

ANGIOSPERMS (flowering plants) Two main classes and recently a third. Two main classes and recently a third. Monocots Monocots Dicots Dicots Eudicots Eudicots Vascular system of angiosperms are much more refined than gymnosperms. Vascular system of angiosperms are much more refined than gymnosperms. Gymnosperms possess trachieds only. Gymnosperms possess trachieds only. Tapered hollow cells that make up the xylem. Tapered hollow cells that make up the xylem. Angiosperms contain tracheids and xylem vessels. Angiosperms contain tracheids and xylem vessels. Xylem vessels are much more efficient is transporting water in all directions. Xylem vessels are much more efficient is transporting water in all directions.

The Flower Structure specialized for reproduction. Structure specialized for reproduction. Fruit is the mature ovary. Fruit is the mature ovary. Seeds develop from the ovules after fertilization. Seeds develop from the ovules after fertilization. Fruits help disperse seeds: Fruits help disperse seeds: Dandelions – flying propeller seeds Dandelions – flying propeller seeds Burrs that cling to animal fur Burrs that cling to animal fur Delicious fruits attract hungry predators that pass the seeds along with a supply of fertilizer. Delicious fruits attract hungry predators that pass the seeds along with a supply of fertilizer.

Vessel Elements Verses Tracheids

The Flower

Reproduction of an Angiosperm The immature gametophytes are contained within pollen grains in the anthers of the stamen. The immature gametophytes are contained within pollen grains in the anthers of the stamen. Each pollen grain has two haploid cells. Each pollen grain has two haploid cells. Ovules develop in the ovary contain the female gametophyte also known as the embryo sac. Ovules develop in the ovary contain the female gametophyte also known as the embryo sac. Pollen sticks to the stigma which is the tip of the of the carpel. Pollen sticks to the stigma which is the tip of the of the carpel.

Angiosperm Reproduction

Evolution of Seed Pods

The Pollen Grain

Angiosperm Seed Dispersal

Fruits The fruit begins to develop after pollination and trigger hormonal signals that cause the ovary to grow and the wall to thicken. The fruit begins to develop after pollination and trigger hormonal signals that cause the ovary to grow and the wall to thicken. The wall is called the pericarp. The wall is called the pericarp. Simple fruit - develops form one ovary (cherry) Simple fruit - develops form one ovary (cherry) Aggregate fruit – single flower with several ovaries or carpels ( raspberry). Aggregate fruit – single flower with several ovaries or carpels ( raspberry). Multiple fruit – develop from several flowers packed together and the ovary walls fuse( pineapple). Multiple fruit – develop from several flowers packed together and the ovary walls fuse( pineapple).

Fruits