Biology p1- bioenergetics

• Photosynthesis

  The process by which plants use sunlight, water and carbon dioxide to create oxygen and energy in the form of sugar
• Photosynthesis equation

  Carbon dioxide + Water + Light energy → Glucose + Oxygen
• To produce glucose molecules by photosynthesis, energy is required
• The reactions in photosynthesis are endothermic (take heat in)
• The energy needed for photosynthesis is supplied by sunlight
• Sunlight is trapped by the green chemical chlorophyll, which is found in chloroplasts
• Factors affecting photosynthesis

  • Temperature
  • Carbon dioxide concentration
  • Light intensity
  • Chlorophyll concentration
• Limiting factor

  The factor that stops the reaction going any faster at any moment
• As temperature increases

  The rate of photosynthesis increases
• As temperature approaches 45°C

  The rate of photosynthesis drops to zero because the enzymes controlling photosynthesis have been destroyed
• As the concentration of CO2 increases

  The rate of photosynthesis increases
• After reaching a certain point, an increase in CO2 has no further effect. CO2 is no longer the limiting factor
• As light intensity increases

  The rate of photosynthesis increases
• After reaching a certain point, any increase in light has no further effect. It is no longer the limiting factor
• Chlorophyll concentration does not vary in the short term but may change if plants are grown in soil without enough minerals to make chlorophyll
• Photosynthesis

  1. Sunlight

  2. Carbon dioxide

  3. Water

  4. Chlorophyll

  5. Glucose
• By looking at a graph, it is possible to identify the limiting factor at any point
• Greenhouses can be used to increase the rate of photosynthesis
• By controlling lighting, temperature and carbon dioxide, farmers can maximise the growth rate of their crops
• Rate of Photosynthesis graph

  • Light intensity is limiting at one point
  • Temperature is limiting at another point
• Investigating the effect of light intensity on the rate of photosynthesis using pondweed

  1. Place pondweed in beaker

  2. Shine light at different distances

  3. Record bubbles in 1 minute
• Variables

  • Independent: light intensity (distance from light)
  • Dependent: number of bubbles in 1 minute
  • Controlled: pondweed, temperature, carbon dioxide
• It is best to take at least two readings at each distance and calculate the mean of the number of bubbles
• Carbon dioxide is provided by adding a small amount of sodium hydrogen carbonate to the water
• Care must be taken to avoid any water being dropped onto the hot light bulb
• Inverse square law

  When light intensity is studied, doubling the distance between the lamp and the pondweed will reduce the light intensity by a quarter
• Converting Glucose

  1. Used in respiration to provide energy

  2. Changed into starch, fats/oils, cellulose, proteins
• To produce proteins from glucose, plants also use nitrate ions, which are absorbed from the soil
• Economical considerations

  Farmers need to work out if the cost of light and heating will be offset by the extra growth that their crops achieve
• Respiration

  An exothermic reaction that releases energy from glucose molecules for use by the body
• Organisms need energy from respiration for

  • Chemical reactions to build larger molecules
  • Movement
  • Keeping warm
• Aerobic respiration

  Respiration with oxygen
• Anaerobic respiration

  Respiration without oxygen
• Aerobic respiration

  Glucose + oxygen -> carbon dioxide + water
• Anaerobic respiration in animals

  Glucose -> lactic acid
• Anaerobic respiration in plants and yeast

  Glucose -> ethanol + carbon dioxide
• Importance of anaerobic respiration in yeast(Fermentation)


  • Produces carbon dioxide for bread making
  • Produces ethanol for alcoholic drinks
• Anaerobic respiration transfers much less energy than aerobic respiration
• The process of anaerobic respiration is different in animals compared to plants and yeast
• Exercise and Respiration

  1. During exercise, the body demands more energy, so the rate of respiration needs to increase

  2. The heart rate, breathing rate and breath volume all increase to supply the muscles with more oxygen and glucose for the increase in aerobic respiration

  3. During periods of vigorous exercise, the muscles may not get supplied with enough oxygen, so anaerobic respiration starts to take place in the muscle cells

  4. This causes a build-up of lactic acid and creates an oxygen debt

  5. The lactic acid causes the muscles to hurt and stops them contracting efficiently. Lactic acid is a poison, so needs to be removed quickly

  6. Once exercise is finished, the oxygen debt must be 'repaid'

  7. After exercise, blood flowing through the muscles transports the lactic acid to the liver where it is broken down