Bioenergetics 1

• Photosynthesis


  1. Uses energy to change carbon dioxide and water into glucose and oxygen

  2. Takes place in chloroplasts in green plant cells

  3. Chloroplasts contain pigments like chlorophyll that absorb light
• Energy transfer


  Energy is transferred to the chloroplasts from the environment by light
• Photosynthesis


  Endothermic process - energy is transferred from the environment
• Photosynthesis (word equation)


  carbon dioxide + water > light > glucose + oxygen
• Photosynthesis (symbol equation)


  6CO2 + 6H2O > light > C6H12O6 + 6O2
• Ways plants use glucose


  • Respiration - transfers energy from glucose
  • Making cellulose - converted into cellulose for plant cell walls
  • Making amino acids - combined with nitrate ions to make amino acids and proteins
  • Stored as oils or fats
  • Stored as starch - insoluble for better storage
• Limiting factors


  • Intensity of light
  • Concentration of CO2
  • Temperature
• Any of the three limiting factors can stop photosynthesis from happening any faster
• At night


  Light is the limiting factor
• In winter


  Temperature is often the limiting factor
• When it's warm enough and bright enough


  The amount of CO2 is usually the limiting factor
• Chlorophyll


  • Can also be a limiting factor of photosynthesis
  • Amount of chlorophyll can be affected by disease or environmental stress, reducing the rate of photosynthesis
• Not enough light

  Slows down the rate of photosynthesis
• Light

  Provides the energy needed for photosynthesis
• As the light level is raised

  The rate of photosynthesis increases steadily
• The rate of photosynthesis only increases up to a certain point
• Beyond that point, increasing light intensity will not make any difference
• Limiting factor

  Either the temperature or the CO2 level
• Changing the light intensity in the lab

  Move a lamp closer to or further away from the plant
• Plotting the rate of photosynthesis against the distance of lamp from plant

  You will get a graph that increases then plateaus
• To get this graph

  Measure the light intensity at the plant using a light meter
• Carbon dioxide

  One of the raw materials needed for photosynthesis
• Too little carbon dioxide

  Slows the rate of photosynthesis
• Photosynthesis rate

  • Increases with CO2 up to a point
  • After a point, the graph flattens out as the amount of CO2 increases, the rate no longer increases
• After the point where the graph flattens out, CO2 is no longer the limiting factor, something else is the limiting factor
• As long as light and CO2 are in good supply, the factor that is limiting the rate of photosynthesis must be temperature
• If the temperature is the limiting factor


  It's because it's too low - the enzymes needed for photosynthesis work more slowly at low temperatures
• If the plant gets too hot


  The enzymes it needs for photosynthesis and its other reactions will be damaged
• This happens at about 45 °C (which is pretty hot for outdoors, although greenhouses uses can can get that hot if you're not careful)
• What are the four limiting factors of Photosynthesis?


  Light Intensity , Temperature , Concentration of Carbon dioxide and the amount of chlorophyll
• Chloroplasts contain chlorophyll which absorbs light energy from sunlight
• How can the rate of Photosynthesis be affected through Chlorophyll?


  Disease (The tobacco mosaic virus) , Environmental Stress and Lack of nutrients

  Due to this the Chloroplasts are damaged which mean Sunlight can't be absorbed as efficiently

  
• Carbon Dioxide enters the leaf via stomata
• Respiration


  A process that supplies the energy needed for biological processes
• Respiration is an exothermic reaction because it releases energy and it takes place continually in all living cells
• Aerobic respiration


  • Glucose is reacted with oxygen gas to produce carbon dioxide and water, and it releases energy
• Aerobic respiration releases a great deal of energy because the glucose molecule has been fully oxidized
• Anaerobic respiration in muscles


  • Glucose is converted to lactic acid, and it does not require oxygen
• Anaerobic respiration releases much less energy than aerobic respiration because the oxidation of glucose is incomplete
• Anaerobic respiration in plant cells and yeast cells

  • Glucose is converted to ethanol and carbon dioxide, and it does not require oxygen