Photosynthesis and limiting factors

• Photosynthesis


  Uses energy to change carbon dioxide and water into glucose and oxygen
• Photosynthesis


  • Takes place in chloroplasts in green plant cells
  • Chloroplasts contain pigments like chlorophyll
• Endothermic


  Energy is transferred from the environment in the process
• Photosynthesis


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


  Carbon dioxide + water -> glucose + oxygen
• Ways plants use glucose

  • For respiration
  • Making cellulose
  • Making amino acids
  • Stored as oils or fats
  • Stored as starch
• Starch is insoluble, which makes it much better for storing than glucose
• Limiting factors affecting the rate of photosynthesis

  • 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 for photosynthesis
• In winter, temperature is often the limiting factor for photosynthesis
• If it's warm enough and bright enough, the amount of CO2 is usually limiting for photosynthesis
• Chlorophyll


  • Can also be a limiting factor of photosynthesis
  • Amount of chlorophyll in a plant can be affected by disease or environmental stress
• Reduced chlorophyll means the rate of photosynthesis is reduced
• Rate of Photosynthesis


  • Light, CO2, and temperature all affect the rate of photosynthesis
• Factors affecting rate of photosynthesis

  1. Light

  2. CO2

  3. Temperature
• Light


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

  Rate of photosynthesis increases steadily, but only up to a certain point
• Beyond a certain light level

  Rate of photosynthesis will no longer increase
• Changing light intensity in the lab


  Move a lamp closer to or further away from the plant
• Plotting rate of photosynthesis against "distance of lamp from the plant" gives a weird-shaped graph
• CO2


  One of the raw materials needed for photosynthesis
• As CO2 amount increases

  Rate of photosynthesis increases up to a point, then flattens out
• If light and CO2 are in plentiful supply, then temperature is the limiting factor
• Temperature


  • If too low, enzymes work more slowly
  • If too high, enzymes get damaged
• Enzymes get damaged at around 45°C
• Greenhouses can get that hot if not careful
• Photosynthesis equation


  Carbon dioxide + Water -> Glucose + Oxygen
• Sunlight


  Energy source for photosynthesis
• Chlorophyll


  Green pigment in chloroplasts which absorbs sunlight
• Stomata


  Pores on leaf where gasses enter and leave
• Starch


  Glucose from photosynthesis is stored as this
• Boil in water


  First step in starch test to kill leaf
• Boil in ethanol


  Second step in starch test to remove chlorophyll
• Dip in hot water

  Third step in starch test to soften leaf
• Cover in iodine


  Final step in starch test to test for Starch
• Blue/Black


  Positive result for starch test with iodine
• Brown


  Negative result for starch test with iodine
• De-starch


  Place plant in dark for 48 hours to remove starch
• Soda Lime


  Chemical that absorbs carbon dioxide