topic 4- bioenergetics

• Photosynthesis


  Process that uses energy from light to change carbon dioxide and water into glucose and oxygen
• Photosynthesis

  • Takes place in chloroplasts in green plant cells
  • Chloroplasts contain pigments like chlorophyll that absorb light
  • Photosynthesis is endothermic - energy is transferred from the surroundings in the process
  • Energy is transferred to the chloroplasts from the environment by light
• Photosynthesis

  1. Carbon dioxide + water

  2. Light

  3. Glucose + oxygen
• The word equation for photosynthesis is: carbon dioxide + water -> light -> glucose + oxygen
• The symbol equation for photosynthesis is: 6CO2 + 6H2O -> light -> C6H12O6 + 6O2
• Ways plants use glucose

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


  Factors that can limit the rate of photosynthesis (light intensity, CO2 concentration, temperature)
• Any of light, CO2 or temperature can become the limiting factor depending on environmental conditions
• Chlorophyll can also be a limiting factor if it is damaged or not produced in sufficient quantities
• Effect of light intensity on photosynthesis rate

  • Rate increases with light intensity up to a point
  • Beyond that point, light is no longer the limiting factor
• Effect of CO2 concentration on photosynthesis rate

  • Rate increases with CO2 concentration up to a point
  • Beyond that point, CO2 is no longer the limiting factor
• Measuring photosynthesis rate using Canadian pondweed

  1. Place pondweed under light source

  2. Measure volume of oxygen produced over time

  3. Repeat at different light intensities, temperatures or CO2 levels
• Inverse square law

  Light intensity is inversely proportional to the square of the distance from the light source
• Artificially creating ideal conditions for plants

  • Using greenhouses to control temperature
  • Providing supplementary lighting
  • Increasing CO2 levels
• Light intensity


  Formula to calculate light intensity
• 105 au stands for arbitrary unit
• Calculating light intensity

  Given the distance, put that in the formula
• 0.01 au is an arbitrary unit
• Greenhouse


  • Traps the Sun's heat
  • Ensures temperature doesn't become limiting
  • Uses heaters in winter
  • Uses shades and ventilation in summer
• Providing light for plants

  Use artificial light after the Sun goes down to give plants more quality photosynthesis time
• Increasing carbon dioxide levels in greenhouse


  Use a paraffin heater to heat the greenhouse, as the paraffin burns it makes carbon dioxide
• Greenhouse


  • Keeps plants free from pests and diseases
  • Allows farmer to add fertilisers to the soil
• Providing ideal conditions for plants in a greenhouse

  Plants will grow much faster and a decent crop can be harvested much more often
• It's important that a farmer supplies just the right amount of heat, light, etc. for the plants to grow well, but not more than the plants need, as this would just be wasting money
• Respiration


  The process of transferring energy from the breakdown of glucose
• Respiration is not "Breathing In and Out"
• Respiration is the process of transferring energy from glucose, which goes on in every cell in the body continuously
• Respiration


  • It's exothermic - transfers energy to the environment
• Examples of how organisms use the energy transferred by respiration


  • To build up larger molecules from smaller ones
  • In animals to allow muscles to contract
  • In mammals and birds to keep their body temperature steady in colder surroundings
• Metabolism


  All the chemical reactions happening in an organism
• Forming larger molecules from smaller ones

  1. Many small glucose molecules are joined together to form starch (storage molecule in plant cells), glycogen (storage molecule in animal cells), and cellulose (component of plant cell walls)

  2. Glucose is combined with nitrate ions to make amino acids, which are then made into proteins
• Breaking down larger molecules into smaller ones

  1. Glucose is broken down in respiration

  2. Proteins are broken down in digestion to produce amino acids, which are then secreted in urine
• Aerobic respiration


  Respiration using oxygen, the most efficient way to transfer energy from glucose
• Aerobic respiration goes on all the time in plants and animals
• Aerobic respiration


  Glucose + Oxygen → Carbon dioxide + Water
• Anaerobic respiration

  Respiration without oxygen, the incomplete breakdown of glucose
• Anaerobic respiration in muscle cells

  Glucose → Lactic acid
• Anaerobic respiration does not transfer nearly as much energy as aerobic respiration
• Anaerobic respiration in plants and yeast


  Produces ethanol and carbon dioxide instead of lactic acid
• Anaerobic respiration in yeast cells is called fermentation