B4 - Bioenergetics

• Photosynthesis


  Uses energy 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
  • Energy is transferred to the chloroplasts from the environment by light
• Endothermic


  Energy is transferred from the environment in the process
• Photosynthesis


  Carbon dioxide + water -> Glucose + oxygen

  (light)
• Symbol equation for photosynthesis: 6CO2 + 6H2O -> 6CH2O + 6O2
• Ways plants use glucose

  • For respiration
  • Making cellulose
  • Making amino acids
  • Stored as oils or fats
  • Stored as starch
• Glucose is turned into lipids (fats and oils) for storing in seeds
• Glucose is turned into starch and stored in roots, stems and leaves, ready for use when photosynthesis isn't happening, like in the winter
• Starch is insoluble, which makes it much better for storing than glucose a cell with lots of glucose in would draw in loads of water and swell up
• Factors that affect the rate of photosynthesis

  • Intensity of light
  • Concentration of CO2
  • Temperature
• Limiting factor


  A factor that is stopping photosynthesis from happening any faster
• At night it's pretty obvious that light is the limiting factor, in winter it's often the temperature, if it's warm enough and bright enough, the amount of CO2 is usually limiting
• Chlorophyll can also be a limiting factor of photosynthesis. The amount of chlorophyll in a plant can be affected by disease or environmental stress, which can cause chloroplasts to become damaged or to not make enough chlorophyll, reducing the rate of photosynthesis
• Relationship between light intensity and rate of photosynthesis

  • As the light level is raised, the rate of photosynthesis increases steadily - but only up to a certain point
  • Beyond that, it won't make any difference as light intensity increases, the rate will no longer increase because it'll be either the temperature or the CO2 level which is now the limiting factor, not light
• Relationship between CO2 concentration and rate of photosynthesis

  • As the amount of CO2 increases, the rate of photosynthesis will only increase up to a point
  • After this the graph flattens out as the amount of CO2 increases, the rate no longer increases, showing that CO2 is no longer the limiting factor
• Relationship between temperature and rate of photosynthesis

  • If the temperature is too low, the enzymes needed for photosynthesis work more slowly
  • If the temperature gets too high, the enzymes it needs for photosynthesis and its other reactions will be damaged, usually at around 45°C
• One graph may show the effect of many limiting factors on the rate of photosynthesis
• The rate of oxygen production by Canadian pondweed corresponds to the rate of photosynthesis
• Experiment to measure effect of light intensity on rate of photosynthesis using Canadian pondweed

  1. Place light source at specific distance from pondweed

  2. Leave pondweed to photosynthesise for set time

  3. Measure length of oxygen bubble produced

  4. Repeat with light source at different distances

  5. Can also measure effect of temperature or CO2 concentration
• Inverse square law


  As distance increases, light intensity decreases in proportion to the square of the distance
• If you halve the distance, the light intensity will be four times greater, and if you double the distance, the light intensity will be four times smaller
• Light intensity can be measured as 1/d^2, where d is the distance
• Greenhouses


  • Help trap the Sun's heat and maintain ideal temperature
  • Can use artificial lighting and increase CO2 levels to create ideal conditions for plant growth
• Light intensity


  102 a.u.
• a.u.


  Arbitrary units
• Calculating the answer


  1. Given the distance, put that in

  2. Light intensity = 102

  3. Calculate the answer

  4. = 0.01 a.u.
• You can Artificially Create the Ideal Conditions for Farming
• Greenhouse


  • Traps the Sun's heat
  • Ensures temperature doesn't become limiting
  • Uses heater in winter to maintain ideal temperature
  • Uses shades and ventilation to cool in summer
• Artificial light


  • Supplied after the Sun goes down to give plants more quality photosynthesis time
• Increasing carbon dioxide level


  • E.g. by using a paraffin heater to heat the greenhouse, as the paraffin burns it makes carbon dioxide as a by-product
• Keeping plants enclosed in a greenhouse

  • Makes it easier to keep them free from pests and diseases
  • Farmer can add fertilisers to the soil to provide all the minerals needed for healthy growth
• Respiration is NOT "Breathing In and Out"
• Respiration


  The process of transferring energy from the breakdown of glucose (sugar), which goes on in every cell
• Respiration is exothermic - it 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 the muscles to contract
  • In mammals and birds, to keep their body temperature steady in colder surroundings
• Metabolism


  All the chemical reactions in an organism
• Enzymes


  • Biological catalysts that control the chemical reactions in a cell
• Reactions where larger molecules are made from smaller ones

  • Glucose molecules joined together to form starch, glycogen, and cellulose
  • Lipid molecules made from one molecule of glycerol and three fatty acids
  • Glucose combined with nitrate ions to make amino acids, which are then made into proteins
• Reactions where larger molecules are broken down into smaller ones

  • Glucose broken down in respiration
  • Excess protein broken down to produce urea, which is then excreted in urine
• Aerobic respiration


  Respiration using oxygen, the most efficient way to transfer energy from glucose