Bio 132 Chp 25- 32

Plants

Early Plants

Adaptation to Land

1. Alternation of Generations

2. Apical meristem (root and shoot)

3. Waxy cuticle

4. Cell walls with lignin

Haplodiplontic life cycle

both haploid and diploid multicellular stages

Gametophyte

multicellular haploid form

Produced gametes via mitosis

Sporophyte

Multicellular diploid form

• Produce “spores” via meiosis

Sporangium

produces spores in seedless plants

Homosporous

produces one type of spores

Heterosporous

produces 2 types of spores

Gametangia

Produces gametes in seedless plants

Apical Meristems

• Site of rapid cell division

• Root tip and shoot tip

• Undifferentiated cells – continued proliferation

• Allows for root and shoot elongation

Lateral meristem

gives trees girth

Vascular tissue

structure and nutrient movement

• Xylem

• Phloem

Xylem

water and ions from root to shoot

Phloem

Food derived via photosynthesis throughout plant

Lignin

adds to strength of tissues

Waxy Cuticle

Prevents H2O loss, stifles CO2 uptake

• Stomata – pores for gas exchange

Additional Adaptations of Land Plants

• Vascular tissue

• Lignin

• Waxy Cuticle

• UV protective flavonoids

• Chemical deterents

Plant Evolution

Paleozoic Era – has six periods

• Cambrian

• Ordovician

• Silurian

• Devonian

• Carboniferous

• Permian

Plant Evolution: Ordovician

colonization of land by plants (> 500 MYA)

Plant Evolution: End of Devonian

Ferns, Horsetails (seedless) and seed plants populated

• Gave rise to trees and forests

• Vegetation enriched air with O2

• Provided food for land animals

Major Divisions of Land Plants

• Non-vascular Plants

• Seedless Vascular Plants

• Seed Plants

  • Gymnosperms

  • Angiosperms

    • Monocots

    • Dicots

Groups of Green Algae

• Charophytes and Chlorophytes

• Chlorophytes

• Charophytes

Charophytes and Chlorophytes

• Same chlorophyll a & b, and carotenoids as land plants – Archaeplastida

• Store carbohydrates as starch (like land plants)

Chlorophytes

sea lettuce and volvox

Charophytes

Chara

Green Algae Structure

single cellular, colonial (even in long chains), multicellular

Cannot survive without thin film of H2O

Groups of Green Algae Reproduction

Asexual – Fragmentation or dispersal of spores

Sexual – fusion of gametes

How Algae differ from plants

Molecular analysis- Land plants and Charophytes = sister groups

Similarities of Land Plants and Charophytes

• Cells divide along cell plates

Plasmodesmata – intercellular channels

Apical growth

Streptophyta

New monophyletic group including land plants and Charophytes

Charophytes

Three groups thought to be closest relatives of land plants:

• Charales

• Zygnematales

• Coleochaetales

Charales

• 420 MYA – freshwater habitats

• Ex. Chara – or Skunkweed – stem has no supportive tissue = not a plant

• Haplontic lifecycle

Zygnematales

• More closely related to embryophytes

• Reproduce sexually and asexually, life cycle haplontic

Bryophytes

• Closest extant relatives of early terrestrial plants (450 MYA)

• 25,000 species ID’d to date

• Thrive in Tundra and other moist habitats

• Lack xylem and lignin (no fossils)

• Life cycle dominated by Gametophyte

Life cycle dominated by Gametophyte

• Male gamete has flagella

• Sporophyte lives on gametophyte, sporangium barely noticeable

Liverworts (Hepaticophyta)

• Most closely related to ancestor of vascular plants – terrestrial

• 7,000 species

• Lobe (like lobe of liver) like flat thallus (some are leafy)

• Organelles allow movement of gas (not stomata)

• Sporophyte contained in archegonium (figure 25.11)

• Asexual reproduction via fragmentation

Hornworts (Anthocerophyta)

• Narrow pipe-like sporophyte

• Sporophytes emerge from gametophyte

• Stomata appear in this group

• Many have symbiotic relationships with cyanobacteria

• Lifecycle follows alternation of generations

Mosses

• More than 10,000 species

• Very abundant on tundra, and bogs

• Sensitive to air pollution and Cu salts

• Gametophyte dominates life cycle

• Lack stomata and vascular tissue

• Anchored to substrate with Rhizoids

• Not major route of H2O absorption

• Sporophyte attached to gametophyte

Tracheophytes

• Vascular plants (>260,000 species)

• Diploid sporophyte is dominant structure

• Seedless vascular plants depend on H2O during fertilization

Tracheophytes

• Vascular Tissue – arose 430 MYA

• Xylem – storage and long distance transport of H2O

  • Tracheids (conducting cells) supportive filler tissue

  • Tracheids incorporate lignin – gives rigid strength

• Phloem – Transports sugars, proteins, solutes throughout plant

  • Sieve elements (conducting cells), supporting cells

Parts of Seedless Plants- Roots

• Roots – evolved after vascular tissue

  • Absorb H2O and nutrients, anchors plant, Symbiosis with Fungi

Leaves, Sporophylls and Strobili

• Microphylls (350 MYA)

  • Single un-branched vein (xylem and phloem) center of leaf

  • Club mosses

• Megaphylls (big leaves)

  • Multiple veins

Sporophylls

modified to bear sporangia

Strobili

Cone-like structures that contain sporangia (conifers)

Ferns and other Seedless Vascular Plants

• Thrived in Carboniferous (360-300 MYA)

• P. Lycophyta (club mosses)

• P. Monilophyta (classes Equisetopsida, Psilotopsida, Polypodiopsida)

  • Equisetopsida – Horsetails

P. Lycophyta (club mosses)

• Earliest seedless vascular plants

• 1,200 sp today

• Lifecycle like moss – except sporophyte is major stage

P. Monilophyta (classes Equisetopsida, Psilotopsida, Polypodiopsida)

• Equisetopsida – Horsetails

• Needle like leaves, photosynthesis in stem

• Silica in stem = rigidity

• Bisexual gametophytes

Psilotopsida – Whisk Ferns

• Lack roots and leaves (reduction – reversal)

• Photosynthesis in stems

Polypodiopsida – True Ferns (20,000 sp)

• Large fronds

  • Photosynthetic

  • Carry reproductive organs (sori = sporangia)

  • Sporophyte is dominant

Importance of Seedless Plants

• Mosses and liverworts - First in primary succession

  • Mosses replenish soil with N2 symbiotic fungi

  • Biological indicators

• Ferns

  • Promote weathering of rock, slow erosion

• Peat moss – bog plant used as fuel

  • Cultivate blueberries and cranberries, used in floral arrangements

• Provided food for land animals

Moving Toward Seed plants

• Dominant sporophyte generation

• Reduction in gametophyte to microscopic

• Heterosporous

• Seeds and Pollen distinguish seed plants

Heterosporous

unlike seedless plants, gametophytes not free living

Megaspore

develop into female gametophytes – produce eggs

Microspores

develop into male gametophytes – produce sperm

First Seed Plants

• Distinct seed plants 350 MYA

• Gymnosperms – 319 MYA (Pennsylvanian period) •

  • Dominated Early Triassic (240 MYA) and mid Jurassic (205 MYA)

• Angiosperms – dominated beginning mid Cretaceous (100 MYA)

Gymnosperm Evolution

• Seed Ferns

• Progymnosperms- Devonian Period (390 MYA)

• Permian dry – advantage seed plants

• Remain dominant plants in Tiaga (N. Boreal Forest), Alpine

Seed Ferns – first seed plants (ex. Elkinisia polymorpha)

• 400 MYA, produced seeds along branches in cupules (protected ovule)

• Seed ferns diversified Carboniferous (coal swamps)

Permian dry – advantage seed plants

• Ginkgoales (Ginkgo biloba) first gymnosperms in Jurrasic

• Gymnosperms expanded in Mezozoic (240 MYA)

Seeds

• Baby in a box with a lunch

• Embryo in a protective coating with a nutrient store

• Can maintain dormancy up to thousands of years

• Protective coat prevents desiccation

• Allow dispersal in space and time

  • Wind, Animals, water

  • Dispersal avoids competition

Pollen grains

male gametophytes

• Produce pollen (sperm)

• Encased haploid cells to prevent desiccation

• Creates pollen tube on contact with female gametophyte = no H2O

Evolution of Angiosperm

• Not derived from Gymnosperms

• Evolved with Insects (at same time) – second in number to insects

• Monocots, Eudicots, Basal Angiosperms (Water Lily)

• New innovations – Flowers and Fruit

  • Protected site of fertilization and seed development

  • Fertilization, ovary thickens = Fruit

Gymnosperm

"Naked seed" plants

• separate female and male gametes, pollination by wind, presence of tracheids (t-port H2O and solutes)

• Seeds are not enclosed in an ovary (fruit) but are partly sheltered by modified leaves called sporophylls.

Strobilus

A tight arrangement of sporophylls around a central stalk, commonly referred to as a cone (e.g., a pine cone).

Gymnosperm- Mesozoic Era

Dominant

adapted to live where : Fresh H2O is scarce during part of the year and N2 poor soil (like a Bog)

Tracheids

t-port H2O and solutes

Specialized cells in the xylem used for the transport of water and solutes; they are the primary conducting cells in most gymnosperms.

Life Cycle of a Gymnosperm

Heterosporous:

• Monoecious (bisexual)

• Dioecious (unisexual)

Monoecious (Bisexual):

male and female sporangia produced on same plant

Dioecious (Unisexual):

male and female sporangia on separate plants

Life Cycle of Conifer- Monecious

Small male cones and large female cones

• Microsporocysts – Meiosis – Pollen grains (male gametophytes)- 2 sperm cells

• Megasporocyte – Meiosis – gametophyte – traps pollen

• Embryo develops- maybe 2 yrs after pollination

Coniferophyta:

• dominant phyla

• Scale like (needle) leaves, low evaporation, snow slides off

• Pine, Spruce, Fir, Cedar, Yew, Sequoia

• Tracheids but no vessel elements

• Important pulp and timber

Cycadophyta:

• Often mistaken for palms

• Mild Climates

• Pollenated by beetle and not wind

• Common in Mesozoic, now only 100 sp

• Ornamental plants

Ginkgophyta:

• Single species today (Ginkgo biloba)

• Fan shaped leaves

• Cultivated by Chinese Buddhist monks

• Very resistant to pollution

• Separate male and female plants

Gnetophyta:

A group of gymnosperms considered the closest relatives to angiosperms due to vessel elements

• genetically close to conifers

Angiosperm Success:

Attributed primarily to two evolutionary innovations: Flowers (for pollination) and Fruit (for seed protection and dispersal).

Flower:

modified leaves (sporophylls) arranged around a central receptacle.

Perianth:

The collective term for the Sepals (which enclose the bud) and the Petals (which attract pollinators).

Sepals

base of attachment of flower to plant – enclose unopened floral bud

Petals

Inside whorl of sepals – attract pollinators

Gynoecium:

The female reproductive part of the flower

• Multiple Carpels (or a Pistil)

• Stigma (pollen receptacle)

• Style (the neck the pollen tube grows through)

• Ovary (houses the ovules).

Androecium:

The male reproductive part of the flower

• It consists of Stamens, which are made of a Filament (stalk) and an Anther (pollen sac).

Angiosperm Reproduction

• Double fertilization – Zygote (1st), Endosperm (2nd)

• Embryo has radicle (small root) & Cotyledon(s) (leaf like organ)

Double Fertilization:

Zygote (1st), Endosperm (2nd)

A reproductive process where one sperm fuses with the egg to form a diploid Zygote, and a second sperm fuses with two polar nuclei to form a triploid Endosperm (food source for the embryo).

Cotyledon:

A leaf-like organ within the seed that provides nutrients to the developing embryo; also known as a "seed leaf."

Fruit:

Thickened ovary walls that develop after fertilization to aid in seed dispersal. Can be fleshy (berries) or dry (wheat/rice).

• Not all fruits from single ovary

• Aid in dispersal

Diversity of Angiosperms

Anthophyta – single phylum of Angiosperms

Basal Angiosperms – Magnoliidea

• Magnolias, laurels, peppers

• Laurels – avocado, cinnamon, spicebush

Monocots:

Angiosperm group with single cotyledon

• scattered vascular tissue

• no tap root (e.g., grasses, lilies).

Dicots (Eudicots):

A group of angiosperms characterized by two cotyledons

• Flowers in multiples of 4 or 5

• Herbaceous or woody

• Main tap root

• 2/3 of all flowering plants

Herbivory

• Both pollination and herbivory attribute to angiosperm success

Evolutionary Arms Race:

• plant defense and animal feeding

A concept within herbivory where plants develop defenses (toxins, spines) and animals evolve new ways to bypass those defenses.

Mutualism:

A relationship where both species benefit, such as the interaction between Ants and Acacia trees or plants and their pollinators.

Foundation of Human Diets

• Carbohydrates – rice, potato, wheat

• Protein – Beans and nuts

• Fats – seeds, avocado, olives, coconut

• Drinks – Tea, Coffee

• Spices – Pepper, Cinnamon, ….

Ethnobotany:

The study of how different human cultures and populations interact with and make use of indigenous plants.

Bioprospecting:

The search for plant species that may yield new medicines or commercial products.

Heirloom Seeds:

• Preservation of seeds used by human populations

Seeds from plant varieties that have been preserved and passed down by human populations to maintain genetic diversity.

DNA Barcoding:

A molecular technique that uses short, standardized sequences of DNA to quickly identify and catalog plant species.