B8

• Carbon dioxide + water = glucose + oxygen

  6co2 + 6h2O = C6H12O6 + 6O2
• Photosynthesis require energy in form of light to drive the chemical reaction. Photosynthesis is an endothermic reaction
• Light energy is absorbed by chlorophyll
• Palisade mesophyll is adapted to absorb light efficiently. The cells :

  Are packed with many chloroplasts

  Are column-shaped and arranged closely together

  towards upper surface of leaf
• Spongy mesophyll is packed closely for gas exchange. They are covered by thin layer of water
• As stomata open water is lost by transpiration
• Xylem transport water. Phloem transport food
• How to test for starch in a plant / leaf ;

  Dip leaf in beaker of boiling water using forceps to remove waxy waterproof layer and kills it

  Heat leaf in tube of ethanol in beaker of boiling water for 5 minutes to decolourise leaf for visible result

  Wash the leaf in boiling water to soften it and wash ethanol off

  Spread leaf out on white tile to see colour change

  Wearing safety specs cover leaf in iodine drops to protect eyes

  Observe the leaf looking for any colour changes to see if starch is visible

  Draw leaf and colour to show result to see if starch is contained
• 4 limiting factors of photosynthesis :

  Light intensity

  Temperature

  Chlorophyll

  carbon dioxide levels
• As light intensity increase the rate of photosynthesis also increase
• Inverse square law : 2 x distance = 1/ (2x2) = 1/4 light intensity
• Plants use glucose for : respiration

  insoluble starch for storage

  cellulose for cell walls

  amino acids for proteins

  glucose for fats and oils for storage
• To test for glucose use benedict and heat , colour change - red
• To test for starch use iodine , colour change - black
• To test for protein use biuret , colour change - purple
• To test for lipids use Sudan iii, colour change - red floating layer
• Carnivorous plants like pitcher plants, Venus fly traps and sundews are adapted to cope with this
• How can farmers make their crops grow quicker ?

  Faster photosynthesis = more biomass added = quicker growth = less starvation around world
• Warmer increase rate of photosynthesis
• In some greenhouses the plants are grown in a solution of mineral ions of soil so that they can never run out of essential ions. This system is called hydroponics
• In some greenhouses the plants are grown in a solution of mineral ions of soil so that they can never run out of essential ions. This system is called hydroponics
• Using greenhouse can be costly in terms of buildings electricity control systems such as computers but higher yield means higher profit
• In hydroponics nutrients are important such as :

  Nitrates to make proteins

  Phosphate for photosynthesis and repsoration

  Potassium to help enzyme action for photosynthesis and respiration

  Magnesium for photosynthesis