Bioenergetics

• photosynthesis is represented by the equation:

  carbon dioxide + water - (light) glucose + oxygen
• symbol equation for photosynthesis:

  CO2 + H20 --> C6H12O6 +02
• photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplast by light
• factors that affect the rate of photosynthesis:

  • light intensity
  • carbon dioxide concentration
  • temperature
  • amount of chlorophyll
• as the temperature increases the number of collisions increases therefore the rate of photosynthesis increase.
• However, at high temperatures, enzymes are denatured. this can be caused by heat, altered pH or by chemical agents and this will decrease the rate of photosynthesis
• increasing light intensity increase the rate of photosynthesis until some other factor - limiting factor becomes in short supply
• carbon dioxide is a reactan t for photosynthesis so if the concentration of carbon dioxide increase the rate of photosynthesis will therefore increase. at some point a factor may become limiting
• chlorophyll absorb the light energy required to convert carbon dioxide and water into glucose
• leaves with more chlorophyll are better able to absorb the light required for photosynthesis
• if the amount of chlorophyll is increased the rate of photosynthesis increases
• light intensity is proportional to 1/distance2
• These factors interact and any one of them may be the factor that limits photosynthesis.
• Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit.
• The 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 the cell wall

  • used to produce amino acids for protein synthesis.
• To produce proteins, plants also use nitrate ions that are absorbed from the soil.
• cellular respiration is an exothermic reaction which is continuously occurring in living cells.
• The energy transferred supplies all the energy needed for living processes.
• Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy.
• aerobic respiration:

  • uses oxygen
  • yields the most energy
  • most reactions occur in the mitochondria
  • glucose + oxygen --> carbon dioxide + water
• anaerobic respiration:

  • occurs when there is not enough oxygen
  • does not produce as much energy as aerobic respiration
• anaerobic respiration in animals:

  • glucose --> lactic acid
• anaerobic respiration in plant and yeast cells ( fermentations) :

  • glucose --> ethanol + carbon dioxide
  • this reaction is used to make bread and alcoholic drinks
• Organisms need energy for:

  • chemical reactions to build larger molecules

  • movement

  • keeping warm.
• During exercise, the human body reacts to the increased demand for energy.
• The heart rate, breathing rate and breath volume increase during exercise to supply the muscles with more oxygenated blood.
• If insufficient oxygen is supplied anaerobic respiration takes place in muscles. The incomplete oxidation of glucose causes a build-up of lactic acid and creates an oxygen debt.
• During long periods of vigorous activity muscles become fatigued and stop contracting efficiently.
• Blood flowing through the muscles transports the 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 reactions in a cell or the body.
• the energy transferred in the cells by respiration is used in the processes of metabolism to make new molecules. this process are controlled by enzymes
• the energy transferred by respiration in cells is used by the organism for the continual enzyme-controlled processes of metabolism that synthesise new molecules
• Metabolism includes:

  • conversion of glucose to starch, glycogen and cellulose

  • the formation of lipid molecules from a 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.