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B8 Photosynthesis (Glucose (Respiration (glucose is broken down using…

- - - - energy can be used in many metabolic reactions
  - - - glucose is soluble in water
        
        high concentrations of dissolved sugars affects water movement by osmosis
      - starch is insoluble in water
        
        does not affect the water balance of the plant
        
        large amounts can be stored in the plant
      - starch is the main energy store found in cells around the plant
        
        stored in leaf cells to be used when dark or little light
        
        stored in storage organs to help them survive through winter
        
        potato tubers and onion bulbs
  - - - cellulose used to strengthen cell walls
  - - - amino acids built into proteins to be used for enzymes etc.
    - - pitcher plants, Venus flytrap and sundews
      - adapted to live in nitrate -poor soil
        
        obtains nutrients from insects they catch instead of from soil
        
        plants produce enzymes to digest trapped insect
        
        uses the nitrate and other minerals from digested animal protein
  - - - used as an energy store in cells
      - used to strengthen cell wall
      - energy store in seeds
        
        provides new plant with food to respire as it germinates
      - used in cell membrane
    - - potential biofuel
- - - - conditions are much more controllable
        
        temperature is maintained at optimum for enzyme action
        
        atmosphere is warmer inside so photosynthesis increases
        
        artificial lighting increases light levels and extends the hours and months of photosynthesis
        
        carbon dioxide levels increased (during day) to not be limiting
        
        nutrient levels monitored to ensure optimum growth
        
        hydroponics
        
        plants grown in balanced mineral ion solutions instead of soil
        
        mineral ion content can be changed according to growth
  - - - carbon dioxide has been produced overnight in respiration
    - - light levels and temperature rise
  - - - land does not need to be ploughed or prepared
      - in hydroponics, crops are clean and soil-free
      - less staff needed
      - time from seed to harvest is shorter
        
        more crops can be grown per year
      - higher yields from larger crops
    - - conditions controlled by computer software
        
        electricity and gas used to maintain conditions (heating, lighting etc.)
        
        setting up expensive monitoring equipment and alarm systems
    - - all the factors affect whether an enclosed system will increase profit
- - - - energy needed to break bonds > than energy released from making bonds
      - energy is transferred from environment to the chloroplasts
    - - carbon dioxide + water → glucose + oxygen
      - the oxygen by-product is released into the air which we breathe in
      - some glucose is used immediately for respiration
        
        some glucose is converted to insoluble starch for storage
      - 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
      - carbon dioxide is taken in by the leaves
      - water is taken up by the roots
  - - - large surface area to capture light
    - - short diffusion path
    - - xylem brings water to leaves
      - phloem takes glucose away
    - - carbon dioxide to reach cells
      - oxygen to leave by diffusion
    - - regulate opening and closing of stomata for gas exhcange
- - - - photosynthesis takes place when there is light available
        
        during daylight
        
        on sunny days with no shade
      - the brighter the light, the faster the rate of photosynthesis
        
        eventually the rate of photosynthesis plateaus out because something else is the limiting factor
        
        if there is no light, photosynthesis stops, regardless of other conditions
      - Required Practical
        
        Light intensity and rate of photosynthesis
        
        place a boiling tube 10cm away from a light source (LED lamps don't release much heat so temperature won't affect experiment)
        
        the test tube is placed in a beaker of water as a buffer, a heat shield can also be placed to keep temperature constant
        
        fill the boiling tube with sodium hydrogen carbonate solution to release carbon dioxide so it won't be the limiting factor
        
        diagonally cut (to increase SA) 5cm of Elodea or Cabomba pondweed and place into boiling tube
        
        leave the boiling tube at 10cm from lamp for 5 minutes for the pondweed to acclimatise to the conditions around it
        
        start a stop watch and count the number of oxygen bubbles produced in 1 minute
        
        repeat the same distance two more times to calculate the mean number of bubbles in 1 minute
        
        repeat entire experiment but at different distances away from the lamp (20cm, 30cm, 40cm)
        
        Problems
        
        bubbles may be too quick to count
        
        each bubble is not the same size
        
        Solution
        
        collect and measure the total volume of oxygen gas released in one minute
        
        place pondweed under a funnel
        
        catch bubbles in a measuring cylinder filled with water
        
        measure volume of oxygen using the measuring cylinder
        
        Inverse Square Law
        
        as distance between light and plant increases, light intensity decreases
        
        inverse relationship :arrow_up::arrow_down:
        
        relationship is not linear because light spreads out
        
        light intensity is in inverse proportion to distance squared
        
        as distance doubles, photosynthesis rate falls by four times
        
        light intensity ∝ 1/ distance²
    - - temperature affects all chemical reactions by speeding them up
      - as temperature rises, rate of photosynthesis increases
        
        at too high temperatures, enzymes controlling photosynthesis denature
        
        rate of photosynthesis falls at 40-50°C
        
        enzymes do not work effectively at low temperatures, slowing down photosynthesis
    - - the rate of photosynthesis increases with higher carbon dioxide concentrations
      - on sunny days, carbon dioxide is the main limiting factor
        
        most of the carbon dioxide is used up, especially in enclosed spaces
        
        in labs or greenhouses, carbon dioxide levels can be increased artificially
        
        only 0.04% carbon dioxide in atmosphere
        
        plenty of light and high temperature, so lots of photosynthesis
      - in the evening, carbon dioxide levels around plant increases
        
        plant respires but does not photosynthesise in the dark
    - - the rate of photosynthesis drops if chlorophyll is limited in the leaf
        
        variegated leaves have chlorophyll-free, white patches
        
        magnesium deficiency means chlorophyll cannot be made
        
        plant may die if little photosynthesis