Plant nutrition

• Photosynthesis


  1. Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water

  2. Oxygen is made and released as a waste product

  3. The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun
• Photosynthesis


  The process by which plants manufacture carbohydrates from raw materials using energy from light
• The raw materials required for photosynthesis are carbon dioxide and water
• Light energy is not a raw material for photosynthesis
• Photosynthesis word equation


  Carbon dioxide + Water -> Glucose + Oxygen
• Chlorophyll


  • Green pigment found in chloroplasts within plant cells
  • Reflects green light, giving plants their characteristic green colour
  • Absorbs light energy and transfers it into energy in chemicals for the synthesis of carbohydrates, such as glucose
• Photosynthesis will not occur in the absence of chlorophyll
• How the products of photosynthesis are used

  • Converted into starch molecules which act as an effective energy store
  • Converted into cellulose to build cell walls
  • Glucose can be used in respiration to provide energy
  • Converted to sucrose for transport in the phloem
  • As nectar to attract insects for pollination
  • Converted into lipids for an energy source in seeds
  • Converted into amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots
• Glucose molecules won't affect osmosis in cells
• Starch


  Insoluble, used for storage
• Cellulose


  Used for strength in cell wall
• Glucose can be converted into fats and oils for energy storage in seeds
• Glucose can be combined with nitrates from the soil to produce amino acids and proteins
• Photosynthesis produces carbohydrates, but plants contain many other types of biological molecules such as proteins, lipids and nucleic acid (DNA)
• Plants obtain mineral elements in the form of mineral ions actively absorbed from the soil by root hair cells
• Mineral is a term used to describe any naturally occurring inorganic substance
• Magnesium ion (Mg2+) deficiency


  Yellowing between veins of leaves (chlorosis), stunted growth
• Nitrate ion (NO3-) deficiency

  Yellowing leaves
• Magnesium is needed to make chlorophyll, which is needed to absorb light for photosynthesis
• Nitrogen is needed to make amino acids, which are needed to make proteins for growth
• Magnesium


  Needed to make chlorophyll
• Magnesium deficiency


  Causes yellowing between the veins of leaves (chlorosis)
• Nitrate


  A source of nitrogen needed to make amino acids (to build proteins)
• Nitrate deficiency


  Causes stunted growth and yellowing of leaves
• Investigating the need for chlorophyll

  1. Leaf dropped in boiling water

  2. Leaf left in hot ethanol for 5-10 minutes

  3. Leaf dipped in boiling water

  4. Leaf spread on white tile and covered with iodine solution
• In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf
• The white areas of a variegated leaf contain no chlorophyll and when tested only the areas that contain chlorophyll stain blue-black
• The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored
• Investigating the need for light

  1. Plant destarched by placing in dark for 24 hours

  2. Leaf partially covered with aluminium foil and plant placed in sunlight for a day

  3. Leaf tested for starch using iodine
• The area of the leaf that was covered with aluminium foil will remain orange-brown as it did not receive any sunlight and could not photosynthesise, while the area exposed to sunlight will turn blue-black
• Investigating the need for carbon dioxide

  1. Two plants destarched by placing in dark

  2. One plant placed in bell jar with sodium hydroxide (absorbs CO2)

  3. Other plant placed in bell jar with water (control)

  4. Both plants placed in bright light for several hours

  5. Both plants tested for starch using iodine
• The leaf from the plant placed near sodium hydroxide will remain orange-brown as it could not photosynthesise due to lack of carbon dioxide
• The leaf from the plant placed near water should turn blue-black as it had all necessary requirements for photosynthesis
• Pondweed (Elodea or Cabomba)


  Plants usually used to investigate rate of photosynthesis
• Investigating rate of photosynthesis

  1. Oxygen gas produced is released as bubbles from cut end of pondweed

  2. Number of bubbles produced over a minute can be counted to record the rate

  3. More accurate version is to collect oxygen in inverted test tube and measure volume
• Changing light intensity


  Affects rate of photosynthesis
• FACTOR BEING INVESTIGATED


  • DISTANCE OF LAMP
  • TEMPERATURE
• IV


  Can be changed
• CV


  Kept constant
• Investigating the effect of changing light intensity on the rate of photosynthesis

  1. Glass tank filled with water

  2. Lamp

  3. Thermometer to monitor temperature

  4. Inverted boiling tube

  5. Oxygen bubbles produced as photosynthesis occurs

  6. Water with sodium hydrogencarbonate (NaHCO3)