Biodiversity of Plants

• Four major plant groups

  • Bryophyte
  • Pteridophyte
  • Gymnosperms
  • Angiosperms
• Plant Life Cycle


  Alternates between two phases: Sporophyte (produces spores, diploid structure) and Gametophyte (produces gametes, haploid structure)

  
• Diploid


  Cell has two (2n) sets of chromosomes in its nucleus
• Haploid


  Cell has one (1n) set of chromosomes in its nucleus
• Reproduction types


  • Asexual
  • Sexual
• Asexual Reproduction


  Only one parent is required, new organism is produced by mitosis, offspring is genetically identical to parent
• Sexual Reproduction

  Two parents needed, haploid sperm cell fuses with haploid egg cell to produce a diploid zygote, offspring contains combination of parents' DNA and is genetically different
• Advantages of Asexual Reproduction


  • Only one parent required
  • All offspring are genetically identical to parent – if parent is well adapted to environment, all offspring will be well-adapted
  • Lots of offspring can be produced in a short period of time
  • Does not rely on pollinators or dispersion agents
• Disadvantages of Asexual Reproduction

  • No genetic diversity – if conditions become unfavorable all offspring might not survive
  • Poor characteristics in parents will be passed on to offspring
  • Rapid multiplication may lead to overcrowding – increased competition for resources
• Advantages of Sexual Reproduction

  • All offspring are genetically different
  • Genetic diversity allows organism to withstand a variety of conditions
  • Farmers can select organisms with desirable traits & cross-breed with them to enhance these traits
• Disadvantages of Sexual Reproduction

  • Two parents are required
  • Rely on pollinating and dispersal agents to spread their seeds
  • Offspring take a long time to mature – vulnerable to predators/disease & rely on parents for protection and food
• Bryophyta


  Includes mosses, liverworts & hornworts – most primitive terrestrial plants

  
• Bryophyta


  • Commonly found in damp, shady areas
  • Atracheophyta – Plant that does not have vascular tissue

  
• Characteristics of Bryophytes


  • Small (<20cm)
  • Plant body is referred to as a thallus
  • Thallus – does not have true stems, roots & leaves
  • Size is limited due to plants having no conducting tissue (xylem or phloem)
  • Leaves do not contain waxy cuticle – water absorbed directly through leaves
  • Produces spores instead of seeds
  • Reproduction is dependent on water
  • Can reproduce both sexually & asexually
  • Dominant generation – Gametophyte

  
• Structure of Bryophytes


  • Diploid Generation (2n)
  • Haploid Generation (n)
  • Archegonium
  • Antheridium
  • Rhizoids found at base of plant – responsible for anchoring plant to a substrate
  • Not true stem & leaves
  • Leaves often referred to as leaflet
  • Spore producing structure
  • Controls the release of spores
  • Transports water and nutrients to developing capsule for sporogenesis (spore production)

  
• Sexual reproductionprocess


  1. When conditions are "ideal" spores are released through operculum

  2. Spores grow to produce gametophyte generation

  3. After maturation, the male sperm (n) swims across to fertilize the egg (n)

  4. This leads to the production of the capsule structure (2n) in which sporogenesis takes place

  5. Once spores are ripened, they are released via the operculum and the cycle repeats itself
• Asexual Reproduction


  1. Bryophytes reproduce Asexually through fragmentation

  2. A small portion of the moss breaks off and can grow into a new plant if the habitat is suitable

  
• Pteridophyte


  Includes all ferns

  
• Pteridophyte


  • Require a warm, damp, shady habitat
  • Ferns have true leaves, roots and stems
  • Fern leaves contain a waxy cuticle – prevents water loss
  • Contain vascular tissue (Tracheophytes) – can grow taller than mosses
  • Reproduction dependent on water
  • Dominant generation – Sporophyte (2n)
• Fern leaves


  Referred to as a frond

  
• Fern leaves


  • Consist of compound leaves – A leaf divided into smaller leaflets (pinna/pinnae)
  • The smallest segment of a pinna
  • Central supporting axis of leaf

  
• Pteridophyte structure


  • A stalk that attaches a leaf to the plant stem
  • Horizontal stem – not to be confused with rhizoids of mosses
  • Roots that form from non-root plant tissue like stems and leaves – increases water & nutrient uptake
• Sexual reproduction pteridophytes

  1. Ferns produce haploid spores (n) that are released during favourable conditions

  2. Spores grow into a structure called a Gametophyte

  3. Gametophytes produce both eggs and sperm

  4. The sperm cells swim to the egg – fertilisation occurs (2n)

  5. This gives rise to a new fern plant

  
• Sori


  Groups of sporangia found on the underside of a fern frond which contain spores

  
• Sporangia


  Produce and store spores