bioenergetics

• photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light
• 6 (carbon dioxide) + 6 (water) -> 6 (oxygen) + glucose
• rate of photosynthesis : temperature --

  • temperature increases the rate of photosynthesis to a certain point as the reaction is controlled by enzymes
  • once the temperature gets too high, the enzymes denature and the rate decreases
  • temperature also means reactants have more kinetic energy, leading to more successful collisions and more product formed
• rate of photosynthesis : light intensity --

  • the greater the light intensity, the faster the rate of photosynthesis because the plant has more energy to carry out photosynthesis
  • this is will continue until another factor limits the rate of photosynthesis
• rate of photosynthesis : carbon dioxide concentration --

  • carbon dioxide is one of the reactants required for photosynthesis, so the greater the carbon dioxide concentration, the greater the rate of photosynthesis as more glucose can be made
• rate of photosynthesis : amount of chlorophyll --

  • the more chlorophyll, the faster the rate of photosynthesis because chlorophyll is what absorbs light energy meaning more chlorophyll leads to a more energetic and successful reaction
• any factor may become the limiting factor in photosynthesis
• the limiting factor is the condition that restricts an increase in the rate of photosynthesis, regardless if other factors increase
• light intensity = 1 / distance squared
• limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit.
• glucose produced in photosynthesis may be:

  • used for respiration
  • converted into insoluble starch for storage
  • used to produce fat or oil for storage
  • used to produce cellulose, which strengthens cell wall
  • used to produce amino acids for protein synthesis. For protein synthesis, the plant also uses nitrate ions absorbed from the soil
• cellular respiration is an exothermic reaction which occurs continuously in living cells
• the energy transferred in cellular respiration supplies all the energy needed for living processes
• respiration can take place aerobically (using oxygen) or anaerobically (without oxygen) to transfer energy
• organisms need energy for:

  • keeping warm
  • movement
  • chemical reactions to build larger molecules
• in anaerobic respiration the oxidation of glucose is incomplete meaning much less energy is transferred in anaerobic than aerobic, where the oxidation of glucose is complete
• anaerobic respiration in yeast and plant cells:

  • glucose -> carbon dioxide + ethanol
• anaerobic respiration in yeast cells is called fermentation and has economic importance in the manufacture of bread and alcohol
• • during exercise the body responds to the increased demand for energy
  • the breath rate, heart rate and breath volume all increase to supply the muscles with more oxygenated blood
• • if insufficient energy is supplied in exercise, anaerobic respiration takes place in muscles.
  • the incomplete oxidation of glucose causes a buildup of lactic acid and creates an oxygen debt
  • during long periods of vigorous activity, muscles become fatigued and stop contracting effectively due to lactic acid
• • blood flowing through the muscles transports lactic acid to the liver where it is converted back into glucose
  • oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells
• metabolism is the sum of all the chemical reactions in a cell or the body
• the energy transferred by respiration in cells is used by the organism for the continual enzyme-controlled process of metabolism that synthesise new materials
• metabolism includes:

  • conversion of glucose to starch, cellulose and glycogen
  • the formation of lipid molecules from one molecule of glycerol and three molecules of fatty acids
  • the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins
  • respiration
  • breakdown of excess proteins to form urea for excretion