Bioenergetics

• Photosynthesis


  Plants use light for their source of energy. It traps this light energy which is an endothermic reaction because it takes in energy.
• Photosynthesis


  • Takes place in leaves
  • Leaves contain chlorophyll which absorbs light energy
• Photosynthesis


  Carbon dioxide + water ——> glucose + oxygen
• CO2 + H2O ——> C6H12O6 + O2
• Limiting factors for photosynthesis


  • Amount of chlorophyll
  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• As we increase light intensity


  Rate of photosynthesis increases
• As we increase carbon dioxide


  Rate of photosynthesis increases
• As we increase temperature


  Enzymes work faster so rate increases. However if we keep increasing temperature, enzymes denature
• Uses of glucose from photosynthesis


  • Release energy in respiration
  • Produce the insoluble storage molecule starch
  • Convert to fats and oils
  • Produce amino acids for protein synthesis
• Photosynthesis only produces glucose during the day when there's light. Plant cells respire all the time.
• Required Practical 5: Photosynthesis

  1. Start by taking a boiling tube and placing it 10 cm away from an LED light source

  2. Fill boiling tube with sodium hydrogen carbonate solution

  3. Put a piece of pond weed into boiling tube with cut end at the top

  4. Leave for 5 mins to acclimatise to conditions. See bubbles of gas

  5. Start stop-watch and count number of bubbles produced in one min

  6. Repeat 2 more times and calculate the mean

  7. Do whole experiment again but start at 20 cm , 30 cm then 40 cm
• Problems: Number of bubbles can be too fast to count, bubbles aren't always the same size. Instead measure the volume.
• Inverse square law: if we double the distance, the light intensity falls by 4 times.
• Farmers light and heat their greenhouses and add extra carbon dioxide to increase rate of photosynthesis.
• Some gardeners use oil burners
• Respiration


  Energy we need is supplied by a process called cellular respiration. It is an exothermic reaction because it releases energy.
• Aerobic respiration


  Glucose + oxygen ——> carbon dioxide + water releases energy
• Anaerobic respiration in muscles


  Glucose ——> lactic acid
• Anaerobic respiration releases much less energy than aerobic respiration because oxidation of glucose is incomplete.
• Anaerobic respiration in plant and yeast cells


  Glucose ——> ethanol + carbon dioxide
• During exercise


  • Breathing rate and breathing volume increase
  • Heart rate increases to pump oxygenated blood around body
• Oxygen debt


  Amount of extra oxygen the body needs after exercise to remove lactic acid from the muscles
• Metabolism


  The sum of all the chemical reactions in a cell or the body
• Glucose in humans is converted to glycogen
• 1 glycerol molecule with 3 fatty acid molecules form lipids
• Humans don't need to eat a lot of proteins