Chapter 30Chapter 30Plant Diversity II: Plant Diversity II:

Evolution of Seed PlantsEvolution of Seed PlantsAP BiologyAP Biology

Seed PlantsSeed Plants Sporophyte dominantSporophyte dominant

Being diploid allows carrying recessive alleles from one Being diploid allows carrying recessive alleles from one generation to the othergeneration to the other

Eventually, these recessive alleles may be selected forEventually, these recessive alleles may be selected for All heterosporousAll heterosporous

MegasporangiaMegasporangia Nucellus; is solid & fleshy part of the ovule located in the ovary of Nucellus; is solid & fleshy part of the ovule located in the ovary of

the flowerthe flower Produces megaspores (egg cells) that produce female gametophyteProduces megaspores (egg cells) that produce female gametophyte Female gametophyte consists of a group of cells called the embryo Female gametophyte consists of a group of cells called the embryo

sacsac MicrosporangiaMicrosporangia

Polen sacs of an antherPolen sacs of an anther Contain microsporocytes (2n) that produce microspores (n) that Contain microsporocytes (2n) that produce microspores (n) that

produce the male gametophyteproduce the male gametophyte Microspores develop into pollen grains when they divide by mitosis Microspores develop into pollen grains when they divide by mitosis

and are covered with cell wall sporopolleninand are covered with cell wall sporopollenin Pollen grains will germinate and form male gametophytePollen grains will germinate and form male gametophyte

Seed Plants, cont.Seed Plants, cont.

Embryo – multicellular sporophyte that will grow Embryo – multicellular sporophyte that will grow into new plantinto new plant Encased in protective seed coat (derived from outer Encased in protective seed coat (derived from outer

structure called integuments)structure called integuments) Supplied with its own source of food (endosperm or Supplied with its own source of food (endosperm or

cotyledons)cotyledons) Seeds allow embryo to be moved away from parent Seeds allow embryo to be moved away from parent

through wind, water, and animalsthrough wind, water, and animals Truly land plants – not tied to water for pollination; Truly land plants – not tied to water for pollination;

gametophytes or embryos do not require as much gametophytes or embryos do not require as much water for supportwater for support

Integument

Megasporangium(2n)

Megaspore (n)

Unfertilized ovule Fertilized ovule

Spore wall

Male gametophyte(within germinatingpollen grain) (n)

Micropyle

Femalegametophyte (n)

Egg nucleus (n)

Dischargedsperm nucleus (n)

Pollen grain (n)

Seed coat(derived fromintegument)

Embryo (2n)(new sporophyte)

Gymnosperm seed

Food supply(femalegametophytetissue) (n)

Seeded Vascular PlantsSeeded Vascular Plants Gymnosperms – “naked Gymnosperms – “naked

seed”seed” Lack enclosed chambers Lack enclosed chambers

(ovaries) in which seeds (ovaries) in which seeds developdevelop

Seeds form naked on Seeds form naked on surface of modified leaf surface of modified leaf (called a scale)(called a scale)

Economically important Economically important as a lumber sourceas a lumber source

About 900 speciesAbout 900 species

Division: Ginkgophya (Ginkgo)Division: Ginkgophya (Ginkgo) Single extant species – Ginkgo bilobaSingle extant species – Ginkgo biloba Used in Chinese herbal medicinesUsed in Chinese herbal medicines

Grows wild in ChinaGrows wild in China May play a role in a cure for May play a role in a cure for

Alzheimer’s, memory loss, increased Alzheimer’s, memory loss, increased circulationcirculation

Dioescious (“two houses”) – produces Dioescious (“two houses”) – produces pollen and seeds on separate treespollen and seeds on separate trees

Male and female treesMale and female trees Male tree creates small pollen coneMale tree creates small pollen cone Female seed covered by fleshy coat (not Female seed covered by fleshy coat (not

a fruit) that smells a fruit) that smells BAD BAD when rottingwhen rotting

Division: Cycadophyta Division: Cycadophyta (Cycads)(Cycads)

Approximately 100 species; Approximately 100 species; some threatened by habitat some threatened by habitat lossloss

Palm-like appearance (ex: Palm-like appearance (ex: Sago palm)Sago palm)

Beetles and bees used for Beetles and bees used for pollination – plant generates pollination – plant generates heat and odors to attract themheat and odors to attract them

Seeds are quite large, often Seeds are quite large, often brightly colored (red, purple, brightly colored (red, purple, or yellow)or yellow)

Roots possess coralloid roots Roots possess coralloid roots (coral-like in appearance); (coral-like in appearance); contain nitrogen fixing contain nitrogen fixing bacteriabacteria

Large, slow growingLarge, slow growing Seeds of Puerto Rican cycad, Zamia portoricensis

Division: GnetophytaDivision: Gnetophyta

One species in US One species in US (Ephedra)(Ephedra)

Gnetum and Gnetum and Welwitschia other Welwitschia other generagenera

Found in southwest US, Found in southwest US, South America, AfricaSouth America, Africa

Division: Coniferophyta (Conifer)Division: Coniferophyta (Conifer)

Cone bearers – often called Cone bearers – often called evergreens since they retain evergreens since they retain their needle-shaped leavestheir needle-shaped leaves

Most have woody cones; Most have woody cones; yews and junipers have yews and junipers have fleshy, berry-like tissues fleshy, berry-like tissues (called aril)(called aril)

Oldest living organisms Oldest living organisms (Bristle-cone pine)(Bristle-cone pine)

Tallest organisms (Coast Tallest organisms (Coast Redwood)Redwood)

Needles have thick cuticle, sunken stomata, Needles have thick cuticle, sunken stomata, mesophyll without air spaces and veins only in center mesophyll without air spaces and veins only in center of the leaf (why might this be valuable?)of the leaf (why might this be valuable?)

Tracheids (xylem) transport water Tracheids (xylem) transport water Larger in summer than in winterLarger in summer than in winter Have pits at ends to facilitate water movement up tissueHave pits at ends to facilitate water movement up tissue Have secondary cell wallsHave secondary cell walls

Economically important for wood, pulp, turpentine, Economically important for wood, pulp, turpentine, resins, and ornamentalsresins, and ornamentals

Monoecious (“one house”) – male and female cones Monoecious (“one house”) – male and female cones (actually sporophyte tissue) appear on same tree(actually sporophyte tissue) appear on same tree

Division: Coniferophyta (Conifer), cont.Division: Coniferophyta (Conifer), cont.

Division: Coniferophyta (Conifer) Division: Coniferophyta (Conifer) Male ConesMale Cones

Male cone (staminate or pollen cone) Male cone (staminate or pollen cone) produces microspores that develop into produces microspores that develop into male gametophytesmale gametophytes

Each cone made up of a number of small Each cone made up of a number of small sporophylls (scales)sporophylls (scales)

Microsporangia contain microsporocytes Microsporangia contain microsporocytes that undergo meiosis to produce haploid that undergo meiosis to produce haploid microspores microspores

Each microspore divides a number of times Each microspore divides a number of times to form a viable pollen grain (immature male to form a viable pollen grain (immature male gametophyte)gametophyte)

Division: Coniferophyta (Conifer) Division: Coniferophyta (Conifer) Female ConesFemale Cones

Female cones (ovule or seed cones) Female cones (ovule or seed cones) produce megaspores that develop into produce megaspores that develop into female gametophytesfemale gametophytes

The megasporangium and the outer The megasporangium and the outer integuments form the ovuleinteguments form the ovule

Megasporocyte divides meiotically to Megasporocyte divides meiotically to form 4 haploid megaspores (only one form 4 haploid megaspores (only one develops into female gametophyte – develops into female gametophyte – other degenerate)other degenerate)

Within gametophyte tissue, Within gametophyte tissue, archegonia are formed, containing egg archegonia are formed, containing egg cellcell

Conifer Life CycleConifer Life Cycle

Angiosperms – “Vessel Seed”Angiosperms – “Vessel Seed”

Division: AnthophytaDivision: Anthophyta Flowering plantsFlowering plants

Reproductive structure of angiosperms – a cluster of Reproductive structure of angiosperms – a cluster of highly-specialized leaves which participate in reproductionhighly-specialized leaves which participate in reproduction

Diversity of species – partially attributed to Diversity of species – partially attributed to coevolution of plants with animal pollinators (specific coevolution of plants with animal pollinators (specific pollinators = edible fruits)pollinators = edible fruits)

Nearly all our food comes from flowering plantsNearly all our food comes from flowering plants Grains, beans, nuts, fruits, vegetables, herbs, spices, tea, Grains, beans, nuts, fruits, vegetables, herbs, spices, tea,

coffee, chocolate, wine, beer, colacoffee, chocolate, wine, beer, cola

Division Anthophyta, cont.Division Anthophyta, cont. Two classes:Two classes: Monocotyledones (monocots)Monocotyledones (monocots)

Ex: lily, orchid, grass, palm, yucca and grains such as Ex: lily, orchid, grass, palm, yucca and grains such as corn, oats, rice, rye, and wheatcorn, oats, rice, rye, and wheat

Dicotyledones (dicots)Dicotyledones (dicots) Ex: sunflower, bean, snapdragon, carrot, roseEx: sunflower, bean, snapdragon, carrot, rose

Have vessel elements (xylem) for water Have vessel elements (xylem) for water transport instead of tracheidstransport instead of tracheids Vessel elements have perforated or absent end Vessel elements have perforated or absent end

plates to speed transportplates to speed transport Reinforced with fiber cellsReinforced with fiber cells Both tracheids and vessel elements are dead cellsBoth tracheids and vessel elements are dead cells

HeterosporousHeterosporous

Division Anthophyta, cont.Division Anthophyta, cont.

Division Anthophyta, cont.Division Anthophyta, cont. Gametophyte greatly reducedGametophyte greatly reduced

Male gametophytes (pollen) have Male gametophytes (pollen) have only two nuclei – tube nucleus and only two nuclei – tube nucleus and generative nucleusgenerative nucleus

Female gametophyte is reduced to Female gametophyte is reduced to only 7 cells and 8 nucleionly 7 cells and 8 nuclei

Sperm and egg nuclei fuse to Sperm and egg nuclei fuse to form 2n zygote that forms form 2n zygote that forms embryoembryo Other sperm nucleus fuses with Other sperm nucleus fuses with

polar nuclei in center to form a 3n polar nuclei in center to form a 3n endospermendosperm

Two fertilizations take place Two fertilizations take place double fertilizationdouble fertilization

Double FertilizationDouble Fertilization

Division Anthophyta, cont.Division Anthophyta, cont. After fertilization, the ovule After fertilization, the ovule

(female gametophyte) (female gametophyte) develops into a seeddevelops into a seed

The endosperm is either The endosperm is either retained in the seed or retained in the seed or absorbed by developing absorbed by developing cotyledonscotyledons

As the seed develops, the As the seed develops, the ovary begins to mature ovary begins to mature around the seed to form around the seed to form fruitfruit

Angiosperm Flower AnatomyAngiosperm Flower Anatomy

Angiosperm Life CycleAngiosperm Life Cycle