B4- the rate of photosynthesis

• What is the primary energy source for photosynthesis?

  Light
• How does increasing light intensity affect the rate of photosynthesis?

  The rate of photosynthesis increases steadily up to a certain point
• What happens to the rate of photosynthesis beyond a certain light intensity?

  The rate no longer increases even if light intensity is increased
• What factors become limiting when light intensity is no longer increasing the rate of photosynthesis?

  Temperature or CO₂ level
• How can you change the light intensity in a lab experiment?

  By moving the light closer to or further away from the plant
• What is necessary to obtain a proper graph of photosynthesis rate against light intensity?

  You need to measure the light intensity at the plant using a light meter
• What is one of the raw materials needed for photosynthesis?

  CO₂
• How does increasing CO₂ affect the rate of photosynthesis?

  It increases the rate up to a point, after which it flattens out
• What indicates that CO₂ is no longer the limiting factor in photosynthesis?

  The rate of photosynthesis no longer increases with more CO₂
• What is the limiting factor for photosynthesis when light and CO₂ are plentiful?

  Temperature
• Why is low temperature a limiting factor for photosynthesis?

  Enzymes needed for photosynthesis work more slowly at low temperatures
• What happens to enzymes needed for photosynthesis if the temperature gets too high?

  They will be damaged
• At what temperature do enzymes for photosynthesis begin to get damaged?

  About 45˚C
• Why can greenhouses reach damaging temperatures for plants?

  Because they can get too hot if not carefully managed
• What are the three important factors affecting the rate of photosynthesis?

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• What are the effects of light intensity, CO₂ concentration, and temperature on the rate of photosynthesis?

  1. Light intensity:

  • Increases rate up to a point
  • Becomes non-limiting beyond a certain level

  1. CO₂ concentration:

  • Increases rate up to a point
  • Becomes non-limiting beyond a certain level

  1. Temperature:

  • Low temperatures slow down enzyme activity
  • High temperatures can damage enzymes