Plant Biodiversity

• Embryophyta (true plants)


  • Eukaryotic
  • Autotrophic
  • Multicellular
  • Photosynthetic (some parasitic)
  • Cellulose cell wall
  • Plasmodesmata for intercellular exchange
  • Store starch
  • Plastids-chloroplasts containing chlorophyll 'a' + 'b'
  • Terrestrial
  • Carotene + xantophyll
• Diagnostic Feature of Embryophyta

  Protect embryo in parental tissue
• Embryophyta are believed to have evolved from a common ancestor with green algae, but they are distinguished by the features listed
• Kingdom Plantae


  Dominant gametophyte generation
• Non-Tracheophytes


  • Bryophyta (liverworts)
• Tracheophytes


  • Polypodiophyta (ferns)
  • Pinophyta (conifers)
  • Magnoliophyta (flowering plants)
• Alternation of Generations


  Alternation between spore-producing diploid sporophyte and gamete-producing haploid gametophyte
• Spore Production


  1. Spore mother cell (2n)

  2. Meiosis

  3. Spore (n)
• Gamete Production


  1. Mitosis in archegonium/antheridium cell

  2. Male gamete (n)

  3. Female gamete (n)
• General life cycle

  • Sporophyte (2n)
  • Meiosis
  • Spores (n)
  • Gametophyte (n)
  • Mitosis
  • Gametes (n)
  • Fertilisation
  • Zygote (2n)
• Dominant Generation


  More conspicuous and long-term/sustained generation in lifecycle (independent)
• Phylum Bryophyta (mosses, liverworts)


  • Simplest land plants
  • Small, 'leafy', flattened in appearance
  • Still require moist/damp environments
  • Exist as colonies to retain H2O
  • Non-vascular, cannot undergo bulk transport
  • No proper roots, stems or leaves (body = THALLUS)
  • Rhizoids for anchorage only (no absorption)
  • Phyllids = leaf-like structures 1 cell thick, have supportive midrib, no stomata, no waxy cuticle
  • Absorb H2O + nutrients from all over plant surface
  • Prone to desiccation
  • Produce sperm which require medium to swim to female gamete
  • Spores resistant to dry conditions, stay dormant until conditions favourable
  • Very small due to lack of lignified/supportive tissue and no vascular tissue
• Gametophyte (Bryophyta)


  Dominant generation, capable of photosynthesis, sporophyte completely dependent on it for sugars/nutrients
• Reproductive Organs/Gametangia (Bryophyta)


  • Both antheridia (male) and archegonia (female) found in same gametophyte
  • Produce gametes by mitosis of mother cells
  • Paraphyses (sterile hairs) present between to retain H2O/moisture
  • Perichaetial leaf-like structures protect gametangia
• Fertilisation (Bryophyta)


  1. Surface of gamete wet, mature antheridia absorb H2O and burst, releasing sperm

  2. Sperm swim through H2O towards archegonia

  3. Mature archegonium neck canal cells break down, releasing mucilage and chemicals to attract sperm

  4. One sperm fertilises egg within venter, forming diploid zygote

  5. Zygote divides by mitosis, forming multicellular, diploid sporophyte embryo which grows out of archegonium

  6. Placenta develops to supply sporophyte with H2O and nutrients
• Sporophyte (Bryophyta)


  • Dependent on gametophyte, remains attached at base where supplied with nutrients
  • Capable of photosynthesis but loses chloroplasts
  • Grows out of archegonium and consists of seta (thin, flexible, long stalk), capsule containing sporangium with spore mother cells that undergo meiosis to produce spores
  • Peristome teeth surround opening of capsule, calyptra derived from archegonium covers capsule
• Spore Release (Bryophyta)


  1. Calyptra shed

  2. Annulus cells lose H2O, operculum becomes loose and falls off

  3. Peristome teeth lose H2O by evaporation, curl backwards and open capsule

  4. Spores released, small and light with sporopollenin coat to prevent desiccation, dispersed by wind and swaying of seta
• Adaptations of Bryophyta to terrestrial life

  • Produce spores protected by sporopollenin coat, resistant to dry conditions and dormant until conditions favourable
  • Many spores produced, chance some will land on suitable substratum and germinate
  • Do not need soil, rhizoids can anchor to rock
  • Colonise new areas
  • Spores formed by meiosis provide genetic diversity
  • Sperm only released if H2O present, zygote/embryo protected during growth
  • Seta holds capsule higher than gametophyte for better spore dispersal
• Limitations of Bryophyta:
• Tracheophyta (vascular plants)


  • Well-developed vascular tissue for bulk flow
  • Xylem for H2O, solutes and support
  • Phloem for sugar transport
  • Differentiated body with proper leaves, stems and roots for absorption and anchorage
  • Allowing for increased size and better adaptation to terrestrial life
• Tracheophyta


  • Pteridophytes (seedless vascular plants, e.g. ferns)
  • Spermatophytes (seed plants, e.g. conifers, flowering plants)
• Phylum Polypodiophyta (ferns)


  • Vascular plants, do not form seeds
  • Dominant generation is sporophyte
  • Vascular tissue for bulk transport and support, only present in sporophyte
  • Differentiated body with true roots, stems and leaves (fronds)
  • Fronds develop from underground rhizome, have rachis (main axis) and pinnae (leaflets)
  • Sori (clusters of sporangia) on underside of fronds, each sporangium contains diploid spore mother cells which undergo meiosis to form haploid spores
• Spore Release (Polypodiophyta)


  1. Indusium (covering) loses H2O and shrivels, exposing sporangia

  2. Annulus cells lose H2O, causing tension in sporangial wall

  3. Thin-walled stomium cells rupture, breaking open sporangium

  4. Thick-walled annulus cells stick together and flip backwards, catapulting spores
• Gametophyte (Polypodiophyta)


  • Small, simple, heart-shaped undifferentiated body (prothallus)
  • No vascular tissue, only unicellular rhizoids for anchorage
  • Independent and photosynthetic, but needs moist conditions for fertilisation since it produces sperm that must swim
• Fertilisation (Polypodiophyta)


  1. Mature antheridium releases multi-flagellate sperm

  2. Sperm swim through moisture to archegonium

  3. Neck canal cells break down, releasing mucilage and chemicals to attract and guide sperm to egg

  4. Sperm fuses with egg, forming diploid zygote within protected archegonium
• Sporophyte (Polypodiophyta)


  • Embryo develops foot embedded in gametophyte for nutrition
  • Embryo grows horizontally up to apical notch, then develops first leaf and root
  • Once leaves and roots develop, sporophyte becomes independent of gametophyte which then dies away
• Advantages of dominant sporophyte in ferns:
• Limitations of ferns:
• Homaspory


  Producing one type of spore (isospores) which germinate into bisexual gametophytes
• Heterospory


  Producing two different types of spores (microspores and megaspores) which develop into separate male and female gametophytes
• Heterosporous plants (conifers, angiosperms)

  • Microspore develops into male gametophyte (pollen grain)
  • Megaspore develops into female gametophyte (within ovule)
  • Male gametophyte transferred to female reproductive structure, germinating pollen tube to deliver sperm, removing need for swimming sperm
  • Zygote develops into embryo within protective seed, with nutrients (endosperm/cotyledons) and coat
• Homasporous vs Heterosporous life cycles

  Homasporous (bryophytes, ferns): Sex differentiation in gametophyte only, bisexual gametophyte

  Heterosporous (conifers, angiosperms): Sex differentiation in sporophyte stage, separate male and female gametophytes

  Homasporous more prone to self-fertilisation, embryo not protected in seed

  Heterosporous more prone to cross-fertilisation, embryo usually enclosed in protective seed
• Phylum Magnoliophyta (flowering plants)


  • Most adapted to terrestrial life morphologically and reproductively

  Complex vascular tissue with xylem vessel elements and phloem sieve tubes with companion cells

  Flowers are the reproductive structures, co-evolved with insects

  Alternation of generations with dominant sporophyte and reduced/microscopic gametophyte

  Endosporic, with embryo obtaining nutrients from endosperm
• Flower parts


  Pedicel: flower stalk

  Peduncle: main stalk of inflorescence

  Receptacle: top of flower stalk where flower parts arise

  Nectaries: glandular structures that secrete nectar to attract pollinators

  Perianth: two whorls of similar segments (tepals) or distinct sepals and petals
• Phylum Magnoliophyta are vascular, seed-bearing plants (spermatophytes) most adapted to terrestrial life morphologically and reproductively, and are the most successful, widespread and diverse
• Phylum Magnoliophyta


  • Complex vascular tissue; proper leaves, roots and stems
  • Main conducting unit of xylem is xylem vessel elements
  • Phloem sieve tubes have companion cells
• Flowers


  • Reproductive structures
  • Heterosporous - produce microspores and megaspores
  • Co-evolved with insects
  • Alternation of generations with sporophyte dominant and gametophyte reduced/microscopic
  • Endosporic
• Pedicel


  Flower stalk which attaches single flower to inflorescence
• Peduncle


  Main stalk of whole inflorescence
• Receptacle


  Top of flower stalk from which flower parts arise