Photosynthesis

• Plants use light as their source of energy for photosynthesis
• Photosynthesis is the reaction plants use to trap light energy
• Photosynthesis is an endothermic reaction
• Photosynthesis takes place in the leaves of a plant, which contain the green chemical chlorophyll
• Chlorophyll absorbs light energy in photosynthesis
• In the first stage of photosynthesis, the plant takes in carbon dioxide and water into the leaf
• Light energy absorbed by chlorophyll is used to convert carbon dioxide and water into glucose and oxygen
• The word equation for photosynthesis is:

  • Carbon dioxide (3CO2) + Water (6H2O) → Glucose (C6H12O6) + Oxygen (3O2)
• Chemical formulas for molecules in photosynthesis:

  • Carbon dioxide: CO2
  • Water: H2O
  • Glucose: C6H12O6
  • Oxygen: O2
• Increasing light intensity increases the rate of photosynthesis
• If light intensity is increased and the rate of photosynthesis also increases, it indicates that light intensity was the limiting factor
• At a certain point, light intensity stops increasing the rate of photosynthesis, indicating another factor is limiting, such as carbon dioxide levels
• Increasing carbon dioxide levels also increase the rate of photosynthesis
• Factors affecting the rate of photosynthesis:

  • Amount of chlorophyll in the leaf affects the rate of photosynthesis
  • Temperature affects the rate of photosynthesis; enzymes work faster with increased temperature, but denature at very high temperatures
• Glucose produced in photosynthesis is used in various ways:

  • To release energy in respiration
  • To produce the storage molecule starch
  • To convert to fats and oils for energy storage
  • To create cellulose for the cell wall
  • To produce amino acids for protein synthesis
• Respiration takes place in the mitochondria and occurs all the time in plant cells, even at night
• Starch, the storage molecule, can be converted back to glucose by the plant when needed
• Glucose in many plants is converted to fats and oils like olive oil for energy storage
• Cellulose, found in the cell wall, is made from the glucose produced in photosynthesis
• Amino acids, produced from glucose, are used by plants to synthesize proteins
• To make amino acids from glucose, plants need to absorb nitrate ions from the soil
• Photosynthesis


  The process by which plants make glucose from sunlight
• Endothermic reaction


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


  Carbon dioxide + water → glucose + oxygen
• Factors affecting rate of photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration
  • Amount of chlorophyll
• Measuring oxygen production to calculate rate of photosynthesis

  1. Pondweed in test tube

  2. Capillary tube and syringe

  3. Lamp at measured distance

  4. Measure distance bubble moves to calculate oxygen volume

  5. Control variables except independent variable
• Limiting factor


  An environmental condition (such as light intensity) which, in low levels, restricts any increase in the rate of photosynthesis
• Graphs showing limiting factors

  • One line levelling off showing one limiting factor
  • Two lines showing two limiting factors
  • Three lines showing three limiting factors
• Farmers can use knowledge of limiting factors to enhance greenhouse conditions for greater rate of photosynthesis
• Inverse proportion


  Relationship where one factor increases as another decreases
• Inverse square law


  Light intensity is inversely proportional to the square of the distance
• Uses of glucose from photosynthesis

  • For respiration
  • Converted into starch for storage
  • To produce fat or oil for storage
  • To produce cellulose to strengthen cell walls
  • Combined with nitrates to form amino acids and proteins
• Respiration


  The process of transferring energy from glucose so living processes can occur
• Exothermic


  Energy is transferred to the environment
• Types of respiration


  • Aerobic (with oxygen)
  • Anaerobic (without oxygen)
• Aerobic respiration


  Glucose + oxygen → carbon dioxide + water
• Anaerobic respiration in animals

  Glucose → lactic acid
• Anaerobic respiration in plants and yeast

  Glucose → ethanol + carbon dioxide
• Oxygen debt


  The amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells
• Metabolism


  The sum of all the reactions in a cell or the body, controlled by enzymes