B4 Bioenergetics

• Photosynthesis


  Process that happens in plants and algae where carbon dioxide from the air enters the leaves by diffusion, water from the soil enters the roots by osmosis, sunlight is absorbed by chlorophyll in chloroplasts, and glucose is produced with oxygen as a waste product
• Photosynthesis


  Carbon dioxide + water → glucose + oxygen
• Endothermic reaction


  Energy is transferred from the surroundings to chloroplasts by light
• Uses of glucose produced in photosynthesis

  • Used in respiration to release energy
  • Converted to insoluble starch for storage
  • Used to make fats or oils for energy storage
  • Used to produce cellulose to strengthen cell walls
  • Combined with nitrates to make amino acids for proteins
• Limiting factors in photosynthesis

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
  • Amount of chlorophyll present
• As light intensity increases


  The rate of photosynthesis increases
• When light intensity is no longer limiting


  The rate of photosynthesis does not increase further, carbon dioxide concentration or temperature are limiting
• As carbon dioxide concentration increases

  The rate of photosynthesis increases
• When carbon dioxide concentration is no longer limiting


  The rate of photosynthesis does not increase further, light intensity or temperature are limiting
• As temperature increases


  The rate of photosynthesis increases
• As temperature continues to increase


  The rate of photosynthesis decreases rapidly as enzymes denature
• Measuring the rate of photosynthesis

  • Counting bubbles of oxygen produced per minute
  • Measuring volume of oxygen produced per minute
• Measuring rate of photosynthesis using pondweed

  1. Set up apparatus with pondweed, lamp, and ruler

  2. Add sodium bicarbonate to provide excess carbon dioxide

  3. Move lamp to different distances, wait for rate to stabilize, then count bubbles per minute

  4. Repeat for 5-6 different distances

  5. Plot graph of bubbles per minute vs distance
• Control variables for photosynthesis rate experiment


  • Same pondweed, length, temperature, carbon dioxide concentration
  • Repeat experiment 3 times for each distance to take a mean
• Changing light intensity by changing brightness of bulb


  Affects rate of photosynthesis
• Changing color of light

  Affects rate of photosynthesis, green light has lowest rate
• Inverse Square Law


  Light intensity is proportional to 1/distance^2
• As distance from light source doubles, light intensity decreases to 1/4 of original
• As distance from light source doubles, rate of photosynthesis decreases to 1/4 of original
• Inverse square law


  Light intensity is inversely proportional to the square of the distance from the light source
• Inverse square law example

  1. Distance doubled

  2. Light intensity reduced to a quarter

  3. Photosynthesis rate reduced to a quarter
• Respiration


  Process that provides energy for all living things, it is exothermic and happens continuously in living cells
• Respiration


  • Can be aerobic (using oxygen) or anaerobic (without oxygen)
• Aerobic respiration


  1. Oxygen taken into lungs

  2. Glucose from digestive system transported in blood

  3. Respiration in cells releases energy, CO2 and water
• Aerobic respiration equation


  Glucose + Oxygen → Carbon dioxide + Water
• Anaerobic respiration in animal cells

  Glucose converted to lactic acid, less energy released
• Anaerobic respiration in plant/yeast cells

  Glucose converted to ethanol and CO2, much less energy released
• Fermentation


  Anaerobic respiration in yeast, produces CO2 that makes bread dough rise, also produces ethanol for alcoholic drinks
• Comparison of aerobic and anaerobic respiration in plants, animals and yeast

  • Tick/cross grid
• During exercise


  Breathing rate and heart rate increase to supply more oxygen and glucose for aerobic respiration in working muscles
• Insufficient oxygen during exercise

  Anaerobic respiration occurs, producing lactic acid and an oxygen debt
• Removing oxygen debt after exercise

  Lactic acid transported to liver and converted back to glucose or broken down to CO2 and water
• Metabolism examples


  • Glucose to starch
  • Glucose to cellulose
  • Glucose + nitrates to amino acids
  • Glycerol + fatty acids to lipids
  • Excess amino acids to urea
  • Glucose to glycogen
• Metabolism is the sum of all chemical reactions in a cell or body, including both plants and animals