Topic 3 - Plant Nutrition and Transport

• Define photosynthesis


  The process by which plants use light energy from the sun to convert water and carbon dioxide into the carbohydrate glucose.
• What absorbs energy from sunlight
• Photosynthesis is endothermic or exothermic


  endothermic meaning heat energy is absorbed
• Plants are...


  Autotrophs - can produce own energy (complex molecules) from raw material (simple molecules)

  Producers - make their own food
• Plants use the glucose as a source of energy in respiration. They can also use it to produce...


  Starch - storage

  Lipids - energy storage in seeds

  Cellulose - strengthen cell wall

  Amino acids (alongside nitrates) - make protein
• Photosynthesis word equation


  Carbon dioxide + water --> glucose + oxygen
• Photosynthesis chemical equation


  6CO2 + 6H2O → C6H12O6 + 6O2
• Limiting factors of photosynthesis


  light intensity, carbon dioxide concentration and temperature

  
  

  Limiting factors are factors that prevent photosynthesis from occurring at an optimum fast rate
• Limiting factor of photosynthesis - Temp


  - higher temp = more kinetic energy = more successful collisions between reactants and enzymes that control photosynthesis

  - BUT you can keep increasing the temperature because the enzymes will get denatured
• Limiting factor of photosynthesis - CO2 concentration


  - raw material required for photosynthesis = more CO2 faster rate

  - trend on graph will continue at steady incline, BUT will stop and rate will be constant at a certain point as other factors for photosynthesis will be in short supply
• Limiting factor of photosynthesis - Light intensity


  - More light available = faster rate because light energy is required to turn the raw large molecules into glucose (rate is constant)

  - graph will show increase line BUT will stop and go horizontal at one point as at that point, some other factor for photosynthesis is in short supply
• Other limiting factor of photosynthesis

  Chloroplast number

  Water
• What can affect the chloroplast number?


  Disease - tobacco mosaic virus

  Lack of nutrients (like magnesium)

  Loss of leaves (as the chloroplasts are located on the leaves)
• Leaf structure


  CUTICLE: Waterproof layer - prevents water loss from evaporation + protective layer

  UPPER EPIDERMIS: single layer of cells, thin + transparent - light goes straight through

  PALISADE MESOPHYLL: column shaped + tightly packed tgth = contains many chloroplasts. Most photosynthesis occurs here.

  SPONGY MESOPHYLL: more rounded cells with lots of air spaces between them (for diffusion). Gas exchange takes place here.

  AIR CAVITY: gases from here pass into the spongy layer

  VASCULAR BUNDLE: contains tubes called XYLEM - brings water + mineral salts to the leaf from roots and tubes called PHLOEM - transports sugars (sucrose) + amino acids from where they are made to other parts of plant

  LOWER EPIDERMIS: no thick cuticle. Many tiny holes called stomata allowing gases to directly diffuse in/out.
• What is the movement of food substances around the plant called?

  Translocation
• Describe the opening/closing of the leaf


  Opening/closing:

  The stomata can be open and closed by GUARD CELLS to allow CO2 to diffuse in but also for oxygen to diffuse out

  - also to prevent water loss vis transpiration

  - closes at night

  - opens at day

  ADAPTATION: plants have a lot of stomata on their underside to reduce water loss
• Large SA adaptation to maximise photosynthesis in leaves

  Increased SA = faster diffusion (more space for molecules to diffuse though)
• Vascular bundle has thick cell walls of tissues in the bundles. how is this an adaptation for the leaf

  supports the stem and leaf
• PRACTICAL: Test leaf for starch


  - boil leaf in water bath to STOP chemical reactions

  - dip in ethanol and heat until boiled = gets ride of chlorophyll

  - rinse leaf in cold water + add iodine solution. if starch present leaf will turn blue-black.

  - starch only present if photosynthesis occur
• PRACTICAL: Test leaf for CO2


  - Put plant in SEALED bell jar with SODA LIME

  - the soda lime will absorb all the CO2 out of the air

  - test leaf after leaving plant for a while -> pour iodine solution, will not turn blue-black because photosynthesis cannot occur without CO2
• PRACTICAL: Test leaf for chlorophyll


  use VARIEGATED LEAF (white + green)

  iodine solution will turn GREEN parts blue-black. the white parts will be orange. This is because starch is only presented when photosynthesis occurs (made from carbohydrate) and photosynthesis requires chlorophyll
• PRACTICAL: Test oxygen production to measure rate of photosynthesis


  - use pondweed to measure effect of light intensity on rate of photosynthesis

  - put water + sodium hydrogen-carbonate inside boiling tube alongside pondweed and attach gas syringe on top (to measure volume of oxygen produced

  - Use light source (independent v)

  - control temp + time
• What removes CO2?


  soda lime
• What ensures there is enough CO2?


  Sodium hydrogen-carbonate
• What main 3-4 mineral ions are needed for growth of plant?

  Potassium, nitrates, phosphates (and magnesium)
• Nitrates


  Source of nitrogen needed to make amino acids (for protein). Protein is needed for cell growth.

  Deficiency = stunted growth + leaves turn yellow
• Phosphates


  Contains phosphorous needed for making DNA + cell membranes. Needed for respiration + growth

  Deficiency = poor root growth + leaves turn purple
• Potassium


  Helps enzymes needed for photosynthesis and respiration

  Deficiency = poor flower + fruit growth + discoloured leaves
• Magnesium


  Needed to make chlorophyll for photosynthesis (but required in smaller amounts)

  Deficiency = yellow leaves
• Where do plants get mineral ions for growth?

  Soil