Unit 3

• Plants can make their own food-it's ace. Here's how..
• Photosynthesis


  1. Photosynthesis produces glucose using sunlight

  2. Photosynthesis happens in the leaves of all green plants

  3. Photosynthesis happens inside the chloroplasts

  4. Photosynthesis converts light energy to chemical energy stored in glucose

  5. Photosynthesis produces oxygen
• Word and Symbol Equations for Photosynthesis

  6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
• Limiting Factors


  • Light intensity, CO₂ concentration and temperature can all be the limiting factor
  • The limiting factor depends on the environmental conditions
• Not enough light


  Slows down the rate of photosynthesis
• Increasing light intensity


  Increases the rate of photosynthesis up to a certain point
• Too little CO₂


  Slows down the rate of photosynthesis
• Increasing CO₂ concentration


  Increases the rate of photosynthesis up to a certain point
• Temperature


  • Affects the rate of photosynthesis
  • If temperature is too high, enzymes are destroyed and rate decreases
  • If temperature is too low, it is the limiting factor
• Leaves


  • Broad surface area exposed to light
  • Most chloroplasts in palisade layer near top of leaf
  • Upper epidermis is transparent
  • Network of vascular bundles to deliver water, nutrients and remove glucose
  • Waxy cuticle reduces water loss
  • Stomata allow gas exchange
• You can control the growing environment in a glasshouse to create optimum conditions for photosynthesis
• Plants need carbon dioxide, water and light to photosynthesise
• Nitrates


  Contain nitrogen for making amino acids and proteins, needed for cell growth
• Phosphates


  Contain phosphorus for making DNA, cell membranes, respiration and growth
• Potassium


  Helps enzymes needed for photosynthesis and respiration, needed for flower and fruit growth
• Magnesium is needed in small amounts for making chlorophyll
• Plants can't make minerals, they get them from the soil
• Root hairs


  • Absorb water by osmosis
  • Absorb minerals by active transport
• Transpiration


  1. Evaporation and diffusion of water from plant surface, mainly leaves

  2. Creates transpiration stream drawing water up from roots
• Light intensity


  Higher light increases transpiration rate
• Temperature


  Higher temperature increases transpiration rate
• Wind speed


  Higher wind speed increases transpiration rate
• Humidity


  Lower humidity increases transpiration rate
• A big tree loses about a thousand litres of water from its leaves every day