Plant tissues, organs and systems

• plant tissues are :

  • Epidermal tissue - covers whole plant
  • Palisade mesophyll tissue - where photosynthesis happens
  • Spongy mesophyll tissue - big air spaces for diffusion of gases
  • Xylem and phloem - transportation of water, minerals and food
  • Meristem tissue - growing tips of shoots and roots, able to differentiate into plant cells, allow plant to grow
• leaf:

  • Epidermal tissue - have waxy cuticle to reduce water loss by evaporation
  • Upper epidermis - transparent so light passes through palisade layer
  • Palisade layer - chloroplasts, near top of leaf for light
  • Xylem and phloem - deliver water and nutrients around plant, take away glucose, support structure
  • Tissues of leaf adapted for gaseous exchange - lower epidermis have stomata
  • Guard cells - open and close stomata responding to environment
  • Air spaces in spongy mesophyll increase rate of diffusion
• translocation:

  • phloem cells have columns of elongated cells with small pores in end walls to allow cell sap to flow
  • (translocation) phloem transport dissolved sugars and food from leaves to plant for immediate use or storage
  • transportation goes both ways
• xylem:

  • made up of dead cells joined end to end
  • Strengthened by lignin
  • Carry water and minerals from root to stem to leaves
• transpiration stream:

  • Movement of water from roots through xylem and out leaves
• transpiration:

  • Caused by evaporation and diffusion of water from plants surface
  • Happens in leaves
  • Evaporation causes shortage of water in leaf, so more water is drawn up from rest of plant through xylem vessels to replace
  • More water being drawn from roots, so there is constant transpiration stream through plant
• • Water leaves plant by diffusion
  • More water inside plant than in air outside
• Transpiration affects:

  • Light intensity - brighter light, increased transpiration rate - stomata close when dark, photosynthesis cannot happen in dark so stomata do not need to be open to let carbon dioxide in
  • Temperature - warmer, faster rate of transpiration - particles have more energy
  • Air flow - better air flow, increase transpiration rate - bad air flow, water vapour surrounds leaf, high concentration of water outside and inside leaf, diffusion is slow
  • Humidity - drier air around leaf, increased transpiration rate - like air flow - needs large difference of conc.
• • Estimating rate of transpiration can be done by measuring uptake of water by plant
  • assumed that water uptake is directly related to transpiration
  • Set up apparatus, record starting position of air bubble, start stopwatch and record distance moved by bubble per unit time
  • Keep temperature and humidity constant
• Guard cells:

  • Kidney shape
  • Guard cells fill with water when plant contains lots of water - stomata open so exchange of gases for photosynthesis
  • Guard cells flatten and lose water when plant is short of water - stomata close and stop water loss
  • Thin outer walls and thick inner walls
  • Sensitive to light and close at night to save water
  • Control water loss and gas exchange