From Cell to Organism : Plants

• Plant Systems

  Two main organ systems:

  1. The shoot- stems, leaves, absorb CO2
  2. The Roots- absorbs water and nutrients from the ground
• Tissue Types


  • Dermal - outer protective layer
  • Ground - supports and transports
  • Vascular - xylem and phloem for transport
• Dermal Tissue


  • One cell thick outer layer
  • responsible for gas exchange
  • protection with waxy cuticle
  • has stomata that open and close for gas exchange (guard cells help it)
  • Stomata close when the turgor pressure decreases
• Ground Tissue


  • makes up majority of plant and is under epidermis
  • provides support, where photosynthesis occurs, and stores water and nutrients
  • includes palisade and spongy layers
• Vascular Tissue

  Responsible for the transport of materials throughtout plant

  Two types:

  • Xylem: transports water and minerals (have thick walls)
  • Phloem: transports glucose (have thin walls with end walls)
• Plant Transport


  • Cohesive Forces - attraction between water molecules that help to pull up water
  • Adhesion Forces - attraction between water and other tissues that also pull water up
  • Root pressure - water absorbed by roots creates upward pressure
  • Cohesive forces and adhesive forces combine to be called the transpiration pull
  • Glucose is transported by the pressure-flow theory (transports sugar from an area of a lot of sugar (suger source) to an area of less sugar (sugar sink))
• Tropisms


  Plant growth responses to stimuli like light (phototropism) and gravity (gravitropism)

  • positive = towards
  • negative = away
• Auxin


  Hormone that controls phototropism by promoting cell elongation on the shaded side of the stem
• Multicellular Organisms

  • to become larger, you must be multicellular
  • Advantages

  1. Division of labour- cells get specialzed + carry out fuctions more efficiently
  2. Size- multiple cells work together to allow for efficient exchange and transport of materials
  3. Interdependance- if one cell dies, it can be replaced
• Cellular Adaptations

  Plants also perform mitosis (when cells divide to repair damage)

  • mitosis happens in the meristems (a specialized group of cells that produce shoot and root tissue)
• ground tissue types

  • Palisade layer- tightly packed layer that holds chloroplasts
  • Spongy layer- loosely packed for gas exchange
• Phototropism


  when a plant grows toward or away from light

  
• Gravitropism


  When a plant grows toward or away from gravity