1.5

• Cuticle

  • transparent - allows light through to lower layers containing chlorophyll
  • waxy and waterproof - reduces water loss
• Palisade layers


  cells are packed with chloroplasts for photosynthesis
• Phloem


  transports sugar away from leaf
• Xylem


  brings water to leaf
• Guard cells

  • open and close the stomata
  • allow carbon dioxide to enter
  • prevents water loss
• Spongy layer

  • contains large air spaces - allows carbon dioxide to reach palisade cell for photosynthesis
  • cells here contain chloroplasts - for photosynthesis
• Photosynthesis


  carbon dioxide + water --(light energy and chlorophyll)-> glucose + oxygen
• Limiting factors

  • light intensity
  • carbon dioxide concentration
  • temperature
  • water
• Light intensity

  • 1/distance²
  • rate of photosynthesis + light intensity increases
  • standstill occurs due to limiting factors such as temperature and carbon dioxide concentration
• Carbon dioxide concentration

  • rate of photosynthesis + co2 concentration increases
  • standstill occurs due to limiting factors such as temperature and light intensity
• Temperature

  • rate of photosynthesis + kinetic energy increases
  • reaches optimum temperature (around 20 °c )
  • enzyme denatures (around 25 °c)
• Water

  • increasing it doesn't increase the rate of photosynthesis
  • too much will kill the plant by driving oxygen out of the soil - killing the roots of the plant
• Phloem structure

  • two way flow of water and food - photosynthesis products
  • end walls with perforations
  • sucrose goes down to be glucose in the sink
  • glucose splits into starch which is insoluble and won't effect osmosis and controls the pressure produced

  
• Xylem structure

  • One way flow of water and minerals
  • carries water uptake from root hairs in soil
  • water enters leaf and spongy mesophyll layer
  • water evaporates out of stomata - drawing more water up towards the leaf through the xylem vessel
  • cohesions (each other) and adhesion (walls)
  • walls of vessel are strengthened with lignin

  
• Root hairs

  • water is in higher concentration (lower water concentration) in soil than in the root hair
  • mineral ions are pumped against concentration current, from low to high
  • process requires ATP energy - a product of aerobic respiration

  
• KPN fertilisers


  ensures plants are taking in essential minerals

  • nitrate deficiency - poor plant growth
  • phosphate deficiency - poor root growth
  • potassium deficiency - yellowing of leaf
• Structure of a leaf

  A - cuticle

  B - upper epidermis

  C - palisade layer

  D - phloem

  E - xylem

  F - lower epidermis

  G - guard cells

  H - stoma

  I - spongy layer