C2.5 - Kingdom Plantae

What are Plants?

• Plants are eukaryotic
• Plants have cell walls that contain the carbohydrate cellulose
• Plants carry out photosynthesis, using the pigment chlorophyll to transform sunlight into chemical energy

Importance

• base of almost all food chains
• provide food, fuel, fiber
• basis of medicines
  • aspirin
  • quinine
  • morphine
• release oxygen
• cycle nutrients
• regulate ecosystem processes to
  • clean air
  • purify water
  • absorb carbon
  • detox. soil
• some can clean up pollution
  • i.e. Indian mustard plant
  • can bind Pb, Cr, Cd (cadmium), Ni, Zn, Cu, Se
  • used to clean major pollution leaks

Evolution

• Photosynthetic organisms clustered around nutrient rich shoreline
• Turbulent shoreline resulted in the evolution of multicellular organisms with strong cell walls, holdfasts, tissues
• Land had abundant light, carbon dioxide, oxygen
• Early plants developed water retention and collection systems, roots, leaves with a waxy cuticle, stomata, vascular system (xylem and phloem tubes)
• xylem: ‘pipes’ carry water and minerals up and act as supports
• phloem: ‘pipes’ carry sap (root foot) down
• pith: cells store sugars and proteins
• cortex and epidermis protect the stem

Cooksonia fossil

• Plants evolved from green algae and share common characteristics
• Invasion of land 430 mya
• Cooksonia fossils one of earliest and simplest plants known
• Key Evolutionary Characteristics
  • formation of embryo (reprod. structure that develops into plant)
  • ability to stand upright and grow tall
    • to get as much sunlight as pssible
  • tissues to transport nutrients, waste, and water
  • strategies to reduce water loss
  • strategies to disperse reproductive structures without water currents
  • lignin: chemical that hardens cell walls

Major Periods of Plant Evolution

Time Period	Key Evolutionary Event	Examples Today
475 mya	Primitive plants evolve from algae; no leaves, stems, seeds, or rigid tissue	Mosses
425 mya	Plants develop lignin and vascular tissues; can grow upright and farther from water	Ferns
365 mya	Seeds develop; protect embryos and allow wider land spread	Seed plants (gymnosperms)
135 mya	Flowers appear; help with reproduction and seed dispersal	Flowering plants (angiosperms)

Alternation of Generations

• life cycle alternating between diploid and haploid forms
• each form distinct, multicellular gens.
• alternation of generations: alternation between haploid and diploid forms
• Haploid Generation
  • gametophyte: plant gametes (egg / sperm cells)
  • prod. of egg and sperm cells
• Diploid Generation
  • sporophyte: plant spores
  • prod. of spores

Green Algae

• modern relatives of plant ancestors
• found in shallow fresh water
• originally classified as Protista
• many green algae have been found to be plants
  • have cell walls
  • and photosynthetic pigments
  • identical to plants

The Bryophytes: Liverworts, Mosses, and Hornworts

• bryophytes: seedless non-vascular plants
• Found in moist environments
• Relatively unspecialized plants
• grow close to the ground in damp locations for easy water access
• NON-VASCULAR plants: plants without xylem or phloem
• no seeds, stems
• no rigid support structures
  • i.e. lignin-reinforced cell walls
• gametophyte dominant generation
  • sperm flagellated and must swim towards eggs

Division Hepatophyta: The Liverworts

• hepato = liver-related
• Simplest plants, small, and inconspicuous
• Lack stomata, cuticle
• Evolutionary branch seperate from other plants
• Sexual reprod. by sports, asexual reprod. by fragmentation
• fragmentation: reproduction by breaking plants apart for new plants to grow

Division Bryophyta: The Mosses

3 classes: Bryidae (true mosses), Sphaginidae (peat mosses), Andreaeidae (granite mosses)

Class Sphaginidae: The Peat Mosses

• Form densely packed peat bogs in cold and temperate regions
• Peat bogs cover 1% of World’s land surface area
• Bogs highly acidic, pH 4 or less
• Peat formed by compression of dead moss
• Peat is absorbent because of pores in dead plants
• Peat can absorb 20x its own dried mass (cf. cotton 4-6x)

Uses of Peat

• Wound dressings (pre-WWI)
• Horticulture: agriculture of plants
• Industrial fuel
• Domestic heating

Seedless Vascular Plants

• No flowers or seeds!
• vascularization: formation of xylem and phloem
• Evolution of conducting tubes (xylem and phloem) solved problem of water and food transport
• Plants could now grow larger
• Underside of gametophyte
  • sperm and egg producing structures
  • sperm flagellated and swim through film of water to eggs
  • sporophyte dominant generation
• 4 Divisions

Division Sphenophyta: The Horsetails

• Mostly extinct, reached max. diversity 300 mya
• One genus survives: Equisetum
• Jointed stems, rough texture from ribs strengthened by silica
• ‘Scouring rushes’

Division Pterophyta: The Ferns

• 11,000 species species, abundant since Carboniferous
• Most diverse group
• Anatomy: fiddleheads, fronds, rhizomes (underground stems)
• Asexual reprod. by fragmentation
• Sexual reprod. by spores

Each brown “dot” on the underside of this fern leaf is made up of many capsules that each contain large numbers of spores.

Seeded Vascular Plants

• Seeds responsible for domination of these plants
• Why? Seed has survival value
  • Guaranteed to grow when planted under right conditions
• Seed protects and feeds plant embryo
• Overall advantage over spores
• 2 types
  • Gymnosperms (naked seed)
  • Angiosperms (vessel seed)

Gymnosperms: The Naked Seed

• gymnosperms: plants that bear “naked” seeds
• “naked” seeds not protected and enclosed in ovary
• 4 divisions
• diploid sporophyte gen. more highly developed than haploid gen.
  • i.e. pine tree is sporophyte
  • gametophytes live in cones
• pollen grain: small male gametophytes that contain cells that develop into sperm
  • adaptation to dry land
• Male gametophyte is the pollen grain
• Transfer of pollen to female gametophyte called pollination

Division Coniferophyta: The Conifers

• Includes pines, spruces, junipers, cedars
• Thin needle-like leaves and thick waxy cuticle reduces water loss
• Well-developed roots
• Basis of many ecosystems
• Economically important in building pulp and paper

Division Cycadophyta: The Cycads

• Palm-like tropical and subtropical plants
• Mesozoic era ‘Age of Dinosaurs and Cycads’
• i.e. Sago Palm

Cycad Fossil

Division Ginkgophyta: The Ginkgos

• One survivor: Gingko biloba, the Maidenhair Tree
• Slow growing tree w/ fan-shaped leaves
• Living trees grown in Chinese and Japanese temples
  • no ginkgos left in the wild

Gingko Fossil

Division Gnetophyta

Welwitschia

• Consists of genuses:
  • Gnetum → tropical trees
  • Ephedra → dry climate shrubs
  • Welwitschia → one species of two-leaved desert plant

Angiosperms

• angiosperms: plants that produce flowers
  • means “enclosed seed”
• The flowering plants
• Over 250,000 species
• Structures to prevent water loss and improve reprod. on land
• Flowers most effective reprod. and speed dispersal structures in Plantae
  • adaptations to attract insects or other animals
  • transfer of pollen flower to flower
  • ovary develops into fruit after pollination
• Seeds enclosed by fruit
• fruit: ripened ovary of a flower
  • attract animals to eat them
  • seeds usually remain undigested and spread through wastes
  • other fruits stick to animals
  • maple keys adapted for wind dispersal
  • coconuts adapted for water dispersal
• Reproduce asexually and sexually
• Sexual repro. produces genetic variability

Classification

• One division: Anthophyta
• Two classes
  • Monocots: one seed leaf, i.e. corn
  • Dicots: two seed leaves, i.e. bean
• Evolution closely tied w/ insects and other pollinators
• Major food source for humans

Monocots vs. Dicots Diagram

Anatomy of Flower: Diagram

Plant Secondary Metabolites

• ‘The plant/insect chemical arms race’
• Plants produce poisonous compounds or bad-tasting compounds
  • i.e. nicotine, caffeine
• Examples
  • Coffee
  • Tea
  • Tobacco
  • Opium
  • Payote (hallucinogen)
  • Marijuana

Climate Change

• transpiration: plants giving off water vapour
  • moves lots of water from ground to atmosphere
• rainforests produce high water vapour, causing rain
• deforestation reduces precipitation
• nearby farmland gets less rain, needs irrigation
• local microclimates and species diversity affected
• ecosystems may recover if damage stops
• heavy deforestation may prevent rainforest regrowth