B4: Bioenergetics

• Photosynthesis


  Process that produces glucose using light
• Photosynthesis

  • Takes place in chloroplasts in green plant cells
  • Uses energy transferred from the environment by light
• Photosynthesis

  1. Carbon dioxide + water

  2. Light

  3. Glucose + oxygen
• Ways plants use glucose

  • Cellular respiration
  • Making cellulose
  • Making amino acids
  • Stored as oils or fats
  • Stored as starch
• Limiting factors

  • Intensity of light
  • Concentration of CO2
  • Temperature
• Chlorophyll can also be a limiting factor of photosynthesis
• Effect of light intensity on rate of photosynthesis

  • Rate increases as light intensity increases, up to a point
  • Beyond that point, increasing light intensity makes no difference
• Effect of CO2 concentration on rate of photosynthesis

  • Rate increases as CO2 concentration increases, up to a point
  • Beyond that point, increasing CO2 concentration makes no difference
• Effect of temperature on rate of photosynthesis

  • Rate increases as temperature increases, up to an optimal temperature
  • Beyond that temperature, enzymes are destroyed and rate decreases
• One graph may show the effect of many limiting factors on the rate of photosynthesis
• Measuring rate of photosynthesis using oxygen production


  1. Place pondweed under light source

  2. Measure volume of oxygen produced over time

  3. Repeat with different light intensities
• Inverse square law

  Light intensity decreases proportionally to the square of the distance from the light source
• Artificially creating ideal conditions for farming

  • Using greenhouses to control temperature, light, and CO2
  • Providing artificial lighting and CO2 sources
  • Controlling pests and diseases
  • Adding fertilizers
• Greenhouse

  • Temperature can be kept at ideal level
  • Artificial light can be supplied after sun goes down
  • Carbon dioxide level can be increased
  • Plants can be kept free from pests and diseases
  • Fertilisers can be added to soil
• Keeping conditions just right for photosynthesis

  Plants will grow much faster and a decent crop can be harvested much more often
• With enough light, photosynthesis can also occur
• Respiration is NOT "Breathing In and Out"
• Respiration


  The process of transferring energy from glucose
• Respiration is exothermic - transfers energy to the surroundings
• Examples of how organisms use energy transformed by respiration

  • To build up larger molecules from smaller ones
  • To allow muscles to contract
  • To keep body temperature steady in colder surroundings
• Metabolism

  All the chemical reactions in an organism
• Metabolism

  1. Lots of chemical reactions happening all the time

  2. Many reactions linked together to form bigger reactions

  3. Larger molecules made from smaller ones

  4. Larger molecules broken down into smaller ones
• Aerobic respiration


  Needs plenty of oxygen
• Aerobic respiration

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


  Used if there's not enough oxygen
• Anaerobic respiration in muscle cells

  Glucose -> lactic acid
• Anaerobic respiration does not transfer nearly as much energy as aerobic respiration
• Anaerobic respiration is only useful in emergencies, e.g. during exercise
• Anaerobic respiration in plants and yeast

  Glucose -> ethanol + carbon dioxide
• Fermentation

  Anaerobic respiration in yeast cells
• Fermentation is used to make bread and alcoholic drinks
• Carbon dioxide from fermentation makes bread rise
• Fermentation produces alcohol in beer and wine making
• When you exercise

  You respire more to get more oxygen to your muscles
• When you exercise intensely

  Your body switches to anaerobic respiration, leading to lactic acid buildup
• Oxygen debt

  The amount of oxygen your body needs to meet the buildup of lactic acid after anaerobic respiration
• Investigating the effect of exercise on the body

  1. Measure breathing rate and heart rate at different exercise intensities

  2. Plot results in a bar chart
• To reduce the effect of random errors, do the investigation as a group and plot the average pulse rate
• Photosynthesis


  The process by which plants make glucose from sunlight
• Endothermic reaction


  Energy is transferred from the environment to the chloroplasts by light