Plant Biology Study Guide module 8

Plants: The Diversity of Life

Introduction

Land plants evolved from green algae.
Adaptations allowed plants to diversify and colonize the land.
Major themes include diversification, key lineages, the transition to land, and controlling water loss.
Surviving intense sunlight and growing upright in air were crucial adaptations.
Reproducing without water and using animals for pollen and seed dispersal also played a key role.

Plant Ecosystem Services and Uses

Plants produce oxygen.
Plants build and hold soil.
They hold water and moderate climate.
Plants are primary producers.
They provide building material, medicines, and the 5 F’s of agriculture: food, feed, fuel, fiber, and flowers.

Phylogeny of the Plantae

Eukaryotes include fungi, animals, and land plants.
Land plants are monophyletic.
Green algae are the closest relatives to land plants.
Key groups within Plantae:
- Glaucophyta (glaucophyte algae)
- Rhodophyta (red algae)
- Green Algae
  - Ulvophyceae (ulvophytes)
  - Charophyceae (stoneworts)
  - Coleochaetophyceae (coleochaetes)
  - Zygnematophyceae (conjugating algae)
- Land Plants
  - Nonvascular Plants
    - Hepaticophyta (liverworts)
    - Bryophyta (mosses)
    - Anthocerophyta (hornworts)
  - Vascular Plants
    - Seedless Plants
      - Lycophyta (club mosses)
      - Psilotophyta (whisk ferns)
      - Pteridophyta (ferns)
      - Equisetophyta (horsetails)
    - Seed Plants
      - Gymnosperms
        Ginkgophyta (ginkgoes)
        Cycadophyta (cycads)
        Cupressophyta (redwoods et al.)
        Pinophyta (pines et al.)
        Gnetophyta (gnetophytes)
      - Angiosperms
        Anthophyta (angiosperms)

Basic Land Plant Characteristics

Eukaryotes.
Multicellular.
Autotrophic via photosynthesis.
Possess chlorophylls a and b.
Have carotenoids.
Cell walls made of cellulose.
Store energy as starch.
Exhibit alternation of generations in their life cycle.

General Plant Life Cycle: Alternation of Generations

Involves multicellular diploid and haploid stages.
Each generation is named after what it produces.
Key Processes:
- Meiosis: Cell division that produces haploid spores.
- Mitosis: Cell division that maintains the ploidy level (either haploid or diploid).

Alternation of Generations: Trends in Land Plants

The life cycle alternates between a gametophyte (haploid) and a sporophyte (diploid) generation:
- Gametophyte Generation: Produces gametes (via mitosis).
- Sporophyte Generation: Produces spores (via meiosis).

Land Plant Categories

Bryophytes and allies (non-vascular plants):
- Lack vascular tissue.
Ferns and allies (seedless vascular plants):
- Possess vascular tissue.
Gymnosperms (plants with 'naked' seeds):
- Have vascular tissue and seeds.
Angiosperms (flowering plants):
- Have vascular tissue, seeds, and flowers.

Major Taxa of Land Plants

Non-vascular Plants
- Hepaticophyta (liverworts)
- Bryophyta (mosses)
- Anthocerophyta (hornworts)
Seedless Vascular Plants
- Lycophyta (lycophytes)
- Psilotophyta (whisk ferns)
- Pteridophyta (ferns)
- Equisetophyta (horsetails)
Gymnosperms
- Cycadophyta (cycads)
- Ginkgophyta (ginkgo)
- Pinophyta (pines et al.)
- Redwood group (junipers et al.)
- Gnetophyta (gnetophytes)
Angiosperms
- Anthophyta (angiosperms) - Flowering plants

Bryophytes and Allies (Non-Vascular Plants)

First embryophytes (land plants).
Characteristics:
- Low growth form (usually <5 cm).
- Simple water-conducting cells.
- Flagellated sperm.
Major groups: mosses, liverworts, hornworts.

Adaptations to Life on Land

Waxy cuticle: prevents water loss.
Sporopollenin: waterproofs spores and pollen (in seed plants).
Evolution of complex gametangia: protection of gametes and nourishment of the embryo.

Bryophytes - Adaptations to Life on Land details

Waxy Cuticle: A waxy layer that reduces water loss from stems and leaves.
Stomata: Pores that allow gas exchange in photosynthetic tissues; guard cells regulate the opening and closing of stomata.
Leaves cross section

Ferns and Allies (Seedless Vascular Plants)

The first vascular plants.
Characteristics:
- Vascular tissue.
- Larger than bryophytes.
- Flagellated sperm.
Major Groups: ferns, horsetails, lycopods.

Ferns and Allies - Adaptations to Life on Land

Vascular tissue:
- Specialized water-conducting cells.
- Movement of water.
- Structural strength to fight gravity.
Roots:
- Uptake of water and nutrients.
- Anchors plant in place.
Vascular tissue:
- Simple water-conducting cells: Little structural support; found in fossils and present-day mosses.
- First vascular tissue: Some structural support; found in fossils.
- Tracheids: Increased structural support; found in all vascular plants.
- Vessel elements: Found in gnetophytes and angiosperms.
- Primary wall (with cellulose)
- Secondary wall (with lignin)

Ferns and allies - reproduction

Fern Gametophyte?:
Fern Sporophyte?:
Fertilization?:

Gymnosperms (Naked Seeded Plants)

The first seed plants.
Characteristics:
- Pollen.
- Seeds.
- Wood.
- Most have needle-like leaves.
Some Major groups: pines, cycads, ginkgos

Gymnosperms- Adaptations to Life on Land

Wood
- Advantages include structural support and increased height for better sunlight capture
Needle or scale-like leaves
- Advantages include reduced water loss in dry conditions
Heterospory:
- Micro- and mega-spores.
- Pollen is the microgametophyte.
- The ovule is the megagametophyte.
Pollen Advantages?
- No longer tied to water for gametophyte growth OR sperm+egg contact
- Gametes can travel further
Seeds – Advantages?
- Embryo nourishment
- Dispersal
- Dormant phase
Seeds germinate when conditions are favorable
- Factors that can break seed dormancy: temperature, moisture, light, fire

Gymnosperms facts

Immense size
- Largest -General Sherman giant sequoia
- Tallest – Hyperion coast redwood -379 ft
Extreme age
- Bristlecone pines- >5,060 yrs old
Boreal forests (taiga)
Ginkgo biloba
- Living fossil
- Widely planted
- Foul-smelling seeds

Angiosperms (Flowering Plants)

Characteristics:
- Flowers.
- Fruits.
- Broad leaves.
- Amazing diversity.

Angiosperms details

Earth’s most dominant plants for more than 100 million years.
- Diverse group of more than 260,000 species
Why do they dominate?
- Flowers, fruits

Angiosperms: Monocots vs. "Dicots"

Monocots:

Single cotyledon (seed leaf).
Parallel leaf veins.
Floral parts often in multiples of 3.
Scattered vascular bundles in the stem.
Fibrous root system.

Dicots:

Two cotyledons.
Branched leaf veins.
Floral parts often in multiples of 4 or 5.
Vascular bundles arranged in a ring in the stem.
Taproot system.

Angiosperms – flowering plants

Most angiosperms have “perfect” flowers
- Have both carpel (female) and stamen (male) parts of flowers
Some have separate male and female flowers
- On the same plant (monoecious); E.g. Corn, Oaks
- On different plants (dioecious); E.g. Holly (Ilex)

Angiosperms – flowering plants - Pollination syndromes

Flowers attract pollinators:
- Scent (e.g. carrion flower)
  - Smells like rotting flesh
  - Pollinated by flies
- Flower shape (e.g. cardinal flower)
  - Red with long tube containing nectar
  - Hummingbird pollinated
- Flower color (e.g. aster)
  - Often purple or yellow
  - Bee pollinated
- Advantages? Costs?

Angiosperms – flowering plants details

Inconspicuous flowers--wind pollination (e.g. corn, oaks, ragweed, grasses)

Angiosperms – flowering plants - Seed dispersal

Fruits encourage seed dispersal
- Animals eat them (e.g. berries)
  - Seeds pass through the digestive system
- Animals transport them (e.g. burdock)
- Wind carries them (e.g maple samaras, dandelions)
- Advantages? Costs?

Angiosperms – flowering plants - Leaves, adaptations and defenses

Broad leaves capture more sunlight
- Broad leaves vs. needle like leaves
  - Trade-offs: broad leaves vs needle-leaves
- Adaptations to defend against herbivores
  - Thorns, spines, chemical defenses

Angiosperms - flowering plants - Special adaptations

Carnivorous plants
- Low N habitats
- Digestive enzymes
Parasitic plants
- Little to no photosynthesis
- Convergent horizontal gene transfer and cross-talk of mobile nucleic acids in parasitic plants