B4: bioenergetics

• photosynthesis - an endothermic reaction which energy is transferred from the environment by light to chloroplasts, the process by which plants make food
• Equation for photosynthesis:

  carbon dioxide + water <(light)> glucose + oxygen

  6CO2 + 6H2O >> C6H12O6 + 6O2
• Uses of glucose in plants:

  1. Respiration - energy transferred from glucose
  2. strengthening cell walls - glucose converted to cellulose which is used to make strong cell walls
  3. protein synthesis - glucose and nitrate ions from soil used to make amino acids which are made into proteins
  4. energy storage - glucose turned into lipids or insoluble starch to store energy
• factors increasing rate of photosynthesis:

  1. light intensity
  2. carbon dioxide concentration
  3. temperature
  4. amount of chlorophyll
• inverse square law:

  light intensity is directly proportional to 1/ distance squared
• limiting factors of photosynthesis can be controlled in a greenhouse but it costs money
• Respiration - an exothermic reaction of transferring energy from glucose and goes on continuously in living cells
• respiration used for living processes:

  1. contracting muscles for movement
  2. to keep warm (in mammals and birds)
  3. to build up larger molecules from smaller ones
• aerobic respiration - respiration using oxygen, most efficient

  glucose + oxygen > carbon dioxide + water

  C6H12O6 + 6O2 >> 6CO2 + 6H2O
• anaerobic respiration - respiration without oxygen which transfers less energy as glucose isn’t oxidised

  muscle cells: glucose >> lactic acid

  yeast and plant cells: glucose >> ethanol + carbon dioxide
• in yeast cells, anaerobic respiration is called fermentation which is the process used to make alcohol and bread
• metabolism - the sum of all the reactions that happen in a single cell or body
• metabolic reactions use energy from respiration to make new molecules:

  1. glucose and nitrate ions make amino acids then proteins
  2. lipids broken down into glycerol and fatty acids
  3. glucose molecules joined together to make bigger carbohydrates
• exercise> more energy needed> more aerobic respiration needed> more oxygen needed, increasing heart rate, breathing rate and breathing volume increases oxygen to muscles
• oxygen debt - the amount of extra oxygen needed to react with built up lactic acid and remove it from cells
• during vigorous exercise> not enough oxygen> anaerobic respiration in muscles> lactic acid builds up> oxygen debt created> heart and breathing rate stay high after exercise
• The liver also helps dealing with lactic acid as the blood with lactic acid goes to the liver and is converted to glucose while normal blood goes to muscles