plant parts

• Plant Physiology Introduction


  • Cell
  • Tissues
  • Organs
• Vascular transport


  • Light as source of energy
  • Light as source of information
• Plant parts & their functions


  • Life in a box
  • Simple tissues
  • Complex tissues
  • Tissue systems
  • Organs and their modifications
• Plants


  Photoautotrophic: Direct use of sun's energy, CO2 as carbon source
• Animals


  Chemoheterotrophic: Energy & C source: energy-rich organic substances
• Plant cells are unusual for one very important reason (besides chloroplasts): they live in boxes, making up the cell wall
• Plant cells can't move
• Evolution of plant diversity

  • Vascular tissue
  • Seeds
  • Flowers & fruits
• Majority of plants (290,000) are angiosperms
• Pine trees do not make fruits
• There are no non-vascular seed plants
• Angiosperms


  • Monocots
  • Eudicots
• Plant organization


  • Cells
  • Tissues
  • Tissue Systems
  • Organs
• Simple tissues


  Made up of only one cell type
• Complex tissues


  Made up of more than one cell type
• Simple tissues


  • Parenchyma
  • Collenchyma
  • Sclerenchyma
• Parenchyma


  • Very common in plants
  • Alive at maturity
  • Surrounded by a thin & flexible primary cell wall
  • Isodiametric shape
  • Most of metabolic functions of a plant
• In flooded areas, plant roots get oxygen through intercellular spaces (aerenchyma)
• Collenchyma


  • Common only in a few plant families
  • Alive at maturity
  • Unevenly thickened primary cell walls
  • Longer than wide (elongated) shape
  • Flexible and elastic
• Structural support of collenchyma depends on both the cell wall and turgor pressure
• Sclerenchyma


  • Fibres
  • Sclereids
• Sclerenchyma


  • Thin primary cell wall and a very rigid secondary cell wall with lignin
  • Inflexible and inelastic, dead at maturity
• The secondary cell wall is on the inside of the primary cell wall
• Primary cell wall


  Carbohydrates: Cellulose, hemicellulose pectin, Proteins
• Secondary cell wall


  As above (but more structured), Lignin - a phenolic polymer polymerized around cellulose fibrils, Provides stiffness and mechanical strength
• Sclereids in pears (stone cells) have a gritty texture and potential function as defense against predators
• There is a correlation between density of sclereids in Sitka spruce bark and susceptibility to weevil attack
• Commercial uses of plant fibres

  • Rope (hemp), Clothing (ramie), Linen (flax), MDF boards (wood fibres), Bioplastics (ramie)
• Commercial uses of walnut shell abrasives

  • Cosmetics: walnut shell exfoliator, skin-smoothing, Clean surfaces without damaging underlying material, Can absorb contaminants, Renewable and environmentally friendly
• Complex tissues


  • Xylem
  • Phloem
• Xylem


  • Composed of living cells (parenchyma) and dead cells (sclerenchyma, tracheary elements)
  • Parenchyma: active solute transport, defense
  • Sclerenchyma: structural support
  • Tracheary elements (tracheids, vessel elements): water/mineral transport from roots to leaves (passive)
• Wood is a type of xylem
• Tracheids have tapered ends and water moves through pits, while vessel elements are wider, shorter and thinner walled, aligned end to end forming micro-pipes
• The spiral thickenings in vacuum hoses and the lignin encrustation in the secondary cell walls of tracheids and vessel elements provide structural support
• Xylem parenchyma cells


  • Unloading of minerals from vessels and tracheids, Active transport of solutes including hormones like auxin which controls development
• Douglas-fir trees with less auxin have a "broccoli tree" appearance
• Wood


  A type of xylem
• Tracheids


  • Found in all vascular plants, dead at maturity
  • Long, thin cells with tapered ends
  • Water moves through pits
• Vessel elements


  • Found in most angiosperms
  • Wider, shorter, thinner walled
  • Aligned end to end forming micro-pipes
• Xylem parenchyma cells


  • Alive
  • Unloading of minerals from vessels and tracheids
  • Active transport of solutes including hormone (e.g. auxin)