B8+9- photosynthesis

• What type of reaction is photosynthesis

  Endothermic - needs an input of energy from the environment
• Stages of photosynthesis

  1. plant takes carbon dioxide and water into the leaf
  2. Light energy is absorbed by chlorophyll
  3. Light energy is used to convert carbon dioxide and water into glucose
  4. oxygen is also produced
• word equation for photosynthesis

  carbon dioxide + water → glucose + oxygen
• chemical equation for photosynthesis

  6CO2 + 6H2O → C6H12O6 + 6O2
• Effect of light intensity on rate of photosynthesis

  • As light intensity increases rate of photosynthesis increases
  • if we increase light intensity and the rate of photosynthesis also increases that tells us the light intensity was limiting
  • light intensity is a limiting factor
• What happens if we keep increasing light intensity 


  • there is a point where the rate of photosynthesis no longer increases
  • Light intensity is no longer limiting factor
  • Something else is now in short supply - co2
• effect of co2 on rate of photosynthesis

  • as we increase co2 levels rate of photosynthesis increases
  • Co2 is a limiting factor
  • At a certain point photosynthesis no longer increases
  • Co2 is no longer a limiting factor
• how does amount of chlorophyll effect rate of photosynthesis

  • a leaf with patches of chlorophyll can trap less light energy than normal leaves
  • lower rate of photosynthesis
• How does temp effect rate of photosynthesis

  • as we increase temperature enzymes involved in photosynthesis work harder
  • Rate increases
  • If we keep increasing the enzymes denature
• Uses of glucose

  • to release energy in respiration
  • to produce the insoluble storage molecule starch - can be converted back to glucose when needed (night)
  • converted to fats and oils used as a storage form of energy
  • To produce cellulose
• how does glucose produce amino acids

  • amino acids synthesise proteins
  • plants absorb nitrate ions from soil
• Why do farmers want to increase rate of photosynthesis

  Increases crop yields
• How do farmers increase photosynthesis

  • light and heat greenhouses
  • Add extra carbon dioxide
  • The extra cost has to be justified by increase in yield
  • Oil burners release heat and carbon dioxide
• what type of reaction is respiration

  Exothermic - releases energy and takes place continually in all living cells
• what is aerobic respiration

  Glucose + oxygen → carbon dioxide + water

  Releases energy
• How much energy does aerobic respiration release

  A lot because glucose molecule is fully oxidises
• chemical equation for aerobic respiration

  C6H12O6 + 6O2 $\rightarrow$ 6CO2 + 6H2O + energy
• Why do muscle cells use anaerobic respiration

  • need a great deal of energy for contraction
  • Under certain conditions amount of oxygen is limited
  • When there is a shortage of respiration cells respire anaerobically
• Anaerobic word equation

  Glucose → lactic acid (+ energy)
• Why is oxygen not in anaerobic respiration

  • oxidisation of glucose is incomplete
• Anaerobic respiration in yeast cells

  Glucose $\rightarrow$ethanol + carbon dioxide
• What is anaerobic respiration in yeast called

  Fermentation
• Why do humans need energy

  • for movement
  • To keep warm
  • for chemical reactions to build larger molecules
• How is aerobic respiration increased with exercise

  • the body need great deal of energy for muscle contraction
  • Body has to react to increased demand for energy
  • Aerobic respiration increases
  • Body cells require more oxygen
  • To provide extra oxygen breathing rate and volume increase - more oxygen in bloodstream
  • Heart rate increases to pump oxygenated blood around body
• what does lactic acid do

  • causes muscles to become fatigued and stop contracting efficiently
• what is oxygen debt

  • the body as to remove lactic acid from the body
  • Is transported out by blood
  • Then taken to liver and converted back to glucose
  • This process requires oxygen
  • Oxygen debt is amount of extra oxygen needed after exercise to deal with accumulated lactic acid
• How do enzymes use energy

  To synthesise new molecules
• what is metabolism

  The sum of all chemical reactions in the cell/body
• photosynthesis practical

  1. verify relationship between light intensity and rate of photosynthesis
  2. put pond weed in test tube
  3. add sodium hydrogen carbonate (co2)
  4. cut stem at an angle whilst submerged
  5. invert and put in a beaker ensuring there is no air at top
  6. carry out in dark room
  7. position lamp at distance measured with meter ruler
  8. wait 1 min for plant to acclimatise to light intensity
  9. start stop watch and count number of bubbles per minute
  10. change distance and repeat