B4

• Photosynthesis


  Carbon dioxide + water → glucose + oxygen
• Photosynthesis

  Carbon dioxide enters through stomata, water enters through root hair cells
• Photosynthesis reaction


  6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• Photosynthesis

  Endothermic (requires energy)
• Uses of glucose from photosynthesis

  • Make cellulose
  • Stored as starch
  • Used as energy source for respiration
  • Stored as oils (lipids)
  • Used to make amino acids
• Limiting factors of photosynthesis

  • Amount of carbon dioxide
  • Amount of light
  • Presence of chlorophyll (where photosynthesis takes place)
• Investigating the rate of photosynthesis

  1. Pond weed placed upside down in water-filled tube with bung and delivery tube

  2. Syringe attached to delivery tube with clamp

  3. Measure oxygen produced as bubbles

  4. Vary light intensity by changing distance of lamp
• Independent variable


  Distance between lamp and tube
• Dependent variable

  Length/number of bubbles over time
• Controlled variables

  Time, CO₂, temperature (water bath)
• Inverse Square Law


  As distance increases, light intensity decreases inversely proportional to the square of the distance
• Factors affecting the rate of photosynthesis

  • Amount of CO₂
  • Light intensity
  • Chlorophyll
  • Temperature
• Increasing photosynthesis


  Increases food production, more glucose, more biomass, faster growth
• Paraffin heaters release CO₂ (used in greenhouses)
• Benefits of a greenhouse

  • Decreased disease spreading
  • Decreased weeds
  • Fertiliser can be added to soil
• Respiration


  Transfer of energy from glucose, occurs in every cell
• Uses of energy from respiration

  • Muscle contraction
  • Keeping warm
  • Moving minerals into cells in plants
  • Building larger molecules from smaller ones
• Glucose used to form other molecules


  1. Glucose stored as starch/glycogen

  2. Glucose converted to cellulose

  3. Glucose combined with nitrate ions to form amino acids

  4. Glucose and fatty acids form lipids
• Exothermic reactions


  Respiration, breaking down excess protein (urea)
• Metabolism


  The sum of all the chemical reactions that occur in the body
• Aerobic respiration


  Glucose + oxygen → water & carbon dioxide (+35 ATP molecules)
• Anaerobic respiration

  1. Glucose → lactic acid (in muscles)

  2. Glucose → ethanol + carbon dioxide (in plants and fungi)
• Bread making involves fermentation, an incomplete breakdown of glucose
• Removing lactic acid

  Lactic acid + oxygen → carbon dioxide + water
• Oxygen debt


  The amount of oxygen needed to break down the lactic acid
• Effects of exercise on the body

  • Increased muscle contractions
  • Increased energy use from respiration
  • Depletion of glycogen reserves in muscles
  • Increased demand for oxygen and glucose
  • Increased breathing rate
  • Increased heart rate
  • Increased body temperature
  • Increased sweating to cool body down