Plant Nutrition

• Photosynthesis: process by which plants manufacture carbohydrates from raw materials using energy from light
• What are these equations for?

  Photosynthesis

  
• In photosynthesis, carbon dioxide and water is used to produce glucose and oxygen
• In photosynthesis the carbon dioxide diffuses through the open stomata of the leaf of a plant and water is taken up through roots
• Chlorophyll is a dye, which traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage.
• Light is necessary for Photosynthesis:

  • Destarch the plant by keeping it in darkness for 48hrs
  • Place a stencil over part of a leaf
  • Place the leaf in sunlight for 4-6 hours
  • Remove the stencil and test for starch
  • +ve result = parts which received light turn black
  • -ve result = parts which didn’t receive light remain yellow/brown

  
• Carbon Dioxide is necessary for Photosynthesis:

  • Get 2 destarched plants.
  • Cover with jars A & B
  • A: put $NaHCO_3$ (sodium bicarbonate). It produces $CO_2$ .
  • B: put $NaOH$ (sodium hydroxide). It absorbs $CO_2$
  • Keep in sunlight for 6+ hours
  • Perform starch test
  • A turns black
  • B remains orange/brown

  
• Limiting factor: something present in the environment in such short supply that it restricts life processes.
• • As the amount of light increases, the rate of photosynthesis increases (a-b)
  • The limiting factor is light
  • Increasing the amount of light after a certain point has no effect on the rate (c)
  • The limiting factor is now carbon dioxide or temperature

  
• Optimum temperature: thermostatically controlled heaters make the temperature right for enzymes to work
• Optimum light: light has a high intensity for more photosynthesis, the correct wavelengths (red and blue not green) and duration controls production of fruit
• To increase the crop yield, farmers control the limiting factors: $CO_2$ enrichment, optimum temperature and optimum light
• $CO_2$ enrichment: paraffin is burnt to increase $CO_2$ concentration by three times the original amount and doubling the yield
• Xylem = Unidirectional vessel which transports water and dissolved minerals.

  • Walls are made out of waterproof lignin.
  • Water moves up due to transpiration and osmosis

  
• Mineral requirements - Nitrogen:

  • Needed for protein synthesis
  • Deficiency: small plant, slow growth, top leaves pale, bottom leaves dead and roots slightly affected
• Mineral requirements - Magnesium:

  • Needed for chlorophyll synthesis
  • Deficiency: plant lacks chlorphyll, leaves yellow but normal roots
• Nitrogen fertilizers: provide nitrogen in the form of nitrate ions, nitrite ions or ammonium ions. But using fertilisers can lead to eutrophication, which is when the fertiliser is transported by rain and leaches into stagnant water e.g. pond or river