Plants

• There are more than 270 000 species of plants that inhabit Earth today
• Plant characteristics


  • Lack mobility (sessile)
  • Eukaryotic
  • Multicellular
  • Autotrophic - perform photosynthesis
  • Cell walls contain cellulose
• Plants face difficulties with the water to land transition
• Difficulties with the water to land transition

  • Structure: no buoyancy on land to maintain structure
  • Getting nutrients to every cell: no water on land to wash cells with necessary nutrients
  • Danger of drying out
  • Reproduction: no excessive water to wash pollen to the egg; no method that did not rely on water
• Methods of overcoming difficulties with the water to land transition

  1. Firmer stems & trunks with strong cell walls of cellulose provide structure to support taller plants and their more complex conducting tissue

  2. Rhizoids: tiny root like structures

  3. Roots

  4. Leaves that have xylem (dead cells that conduct water and dissolved materials from the roots) and phloem (living cells that transport sugars down the root for storage)

  5. Waxy covering on leaves/needles, cuticle, stops evaporation

  6. Stomata — pores to allow for gas exchange and water to escape

  7. Nectar, colourful and special shapes of flowers, pollen, fruit, spores, seeds with protective coats, various methods of pollen dispersal including: by animal (inside and outside), by wind, by water
• Alternation of generations (sexual reproduction life cycle in plants)

  Plants have 2 stages: a haploid stage that produces gametes (THE GAMETOPHYTE GENERATION) and a diploid stage that produces spores (THE SPOROPHYTE GENERATION)

  
• Bryophytes: The mosses


  • Simplest of land plants
  • Do not have specialized vascular tissue, leaves, roots or seeds
  • Produce swimming sperm (antheridia) and eggs, so can only live and reproduce in moist locations
• Lycophytes and Pterophytes: The ferns


  • Seedless vascular plants
  • Considered "living fossils" because they are the only remaining genus of what was once a diverse group of plants
  • Have simple roots and stems
• The seed plants


  • Dominant land plants on Earth
  • Pollen grains can be carried over long distances before pollination occurs
• Types of seed plants

  • Gymnosperms: coniferous trees. Cones are the reproductive structures
  • Angiosperms: The flowering plants