Plants and Photo synthesis 1.2

• Photosynthesis


  The process by which plants make their own food using light energy
• Photosynthesis


  • Occurs in the Chloroplast inside leaf cells
• Photosynthesis equation


  Carbon dioxide + water → Glucose + oxygen
• Light energy is required for photosynthesis
• De-starching a leaf


  1. Store in a dark cupboard for 48 hours (in darkness to use up the starch)

  2. Test a leaf for starch

  3. Place leaf in boiling water for 3 mins to stop chemical reactions

  4. Place leaf in boiling tube of ethanol to remove chlorophyll

  5. Place leaf back in warm water to soften

  6. Place leaf on white tile and add iodine - if starch is present it will turn blue-black
• The purpose of de-starching a leaf is to remove all the starch that was stored in the plant before the experiment
• Sodium hydratide near a leaf will absorb (o₂ from the air so the plant can't photosynthesise
• If no co₂ no Starch Can be produced
• Factors affecting the rate of photosynthesis


  • Light intensity
  • Co₂ concentration
  • Temperature
• Light intensity


  Affects the rate of photosynthesis
• Carbon dioxide concentration


  Affects the rate of photosynthesis
• Temperature


  Affects the rate of photosynthesis
• Optimum temperature for photosynthesis


  Too high temperatures will denature enzymes
• At bright light conditions and low CO₂ concentration, light intensity can be the limiting factor
• Compensation point


  The light intensity at which the rate of photosynthesis = the rate of respiration
• Carbon dioxide concentration


  Affects the colour of the leaf (high CO₂ - yellow, normal CO₂ - red, low CO₂ - purple)
• Leaf structure


  • Waxy cuticle - transparent to allow light in and prevent water escaping
  • Upper epidermis - physical defence from damage and to allow light in
  • Vascular bundle - Xylem transports water, Phloem transports sugar solution
  • Guard cells surround the stomata and close at night
• Waxy cuticle - It is transparent to allow light in and prevent water escaping
• Upper epidermis - physical defence from damage and allow light in
• Vascular bundle

  • xylem - transplanted
  • phloem - transport sugar solution
• Guard cell - these surround the stomata and close at night (to prevent water loss)
• Palisade mesophyll - packed full of chloroplasts to capture light and carry out photo synthesis
• Spongy mesophyll - spongy texture give large surface area
• Air space - lots of air to allow Co2 to enter the leaf
• Respiration equation

  glucose + oxygen —> carbon dioxide + water + energy