GCSE Biology (B4)

• Photosynthesis


  1. Takes place in the leaves

  2. Takes place in chloroplasts

  3. Chlorophyll absorbs light energy

  4. Converts carbon dioxide and water into glucose and oxygen
• Photosynthesis is an endothermic reaction where energy is transferred from the environment to chloroplasts by light
• Carbon dioxide and water supply for photosynthesis

  1. Carbon dioxide diffuses into leaves through stomata

  2. Water is taken up from soil by roots and transported to leaves via xylem
• Products of photosynthesis


  • Glucose is the main product
  • Oxygen is also produced but not as important
• Uses of glucose produced by photosynthesis

  • Cellular respiration
  • Making cellulose
  • Making starch
  • Making amino acids
  • Making oils and fats
• Plant growth rate is often dependent on the rate of photosynthesis
• Factors affecting the rate of photosynthesis are light intensity, temperature, carbon dioxide concentration, and amount of chlorophyll
• Factors affecting photosynthesis


  • Light intensity
  • Temperature
  • Concentration of carbon dioxide in the air
  • Amount of chlorophyll in plants
• Chlorophyll


  Pigment within chloroplasts that absorbs the light energy needed for photosynthesis
• Plants have less chlorophyll


  They won't be able to carry out as much photosynthesis
• Factors that can reduce chlorophyll levels in plants

  • Disease (e.g. tobacco mosaic virus)
  • Environmental stress
  • Lack of nutrients (e.g. water)
• Cellular respiration is an exothermic reaction which transfers energy from glucose and is continuously occurring in living cells
• Limiting factors for photosynthesis are normally light, carbon dioxide and temperature
• Cellular respiration


  Breaking apart glucose molecules to release the energy that's trapped inside
• Graphing the effect of limiting factors on photosynthesis

  1. Plot light intensity, carbon dioxide concentration or temperature on the x-axis

  2. Plot rate of photosynthesis on the y-axis

  3. Rate increases until it plateaus, indicating another factor is now limiting
• How organisms use their energy

  • Building up larger molecules from smaller ones (e.g. combining amino acids to form proteins)
  • Muscular contraction for movement
  • Maintaining body temperature
• Energy is needed for loads of reactions in our cells, most of which are catalyzed by enzymes
• Metabolism


  All the chemical processes that occur within a living organism in order to maintain life
• Aerobic respiration


  • More common type
  • Takes place whenever there's enough oxygen
  • Most efficient way to transfer energy from glucose
  • Takes place continuously in both plants and animals
  • Takes place within mitochondria
• Aerobic respiration


  Glucose + Oxygen → Carbon dioxide + Water
• As light intensity increases

  Rate of photosynthesis increases
• Exercise


  Causes the body to carry out more cellular respiration
• The equation for aerobic respiration is the opposite of the equation for photosynthesis
• Cellular respiration during exercise

  1. Muscles require more energy

  2. Muscles require more oxygen

  3. Breathing rate and volume increase

  4. Heart rate increases
• As carbon dioxide concentration increases

  Rate of photosynthesis increases
• Insufficient oxygen during intense exercise

  Cells switch to anaerobic respiration
• Anaerobic respiration


  Less efficient than aerobic respiration, produces lactic acid
• Lactic acid buildup during exercise

  Causes a burning sensation in muscles
• Anaerobic respiration


  • Respiration without oxygen
  • Used when there's not enough oxygen to keep up with the demands of aerobic respiration
  • Incomplete breakdown of glucose
  • Leads to lactic acid buildup
• Oxygen debt


  Extra oxygen needed after exercise to react with and remove lactic acid
• As temperature increases initially

  Rate of photosynthesis increases
• Removing lactic acid after exercise

  1. Lactic acid carried in blood to liver

  2. Lactic acid reacted with oxygen and converted back to glucose
• Anaerobic respiration


  Glucose → Lactic acid
• Measuring effects of exercise

  • Measure breathing rate
  • Measure heart rate
• Breathing rate is measured by counting chest rises and falls per minute
• As temperature increases further

  Rate of photosynthesis decreases as enzymes denature
• Heart rate is measured by feeling the pulse in the wrist or neck
• Graphs can show the effect of multiple limiting factors
• Techniques farmers use to optimise photosynthesis

  • Using greenhouses to trap heat and provide artificial light
  • Pumping in carbon dioxide
  • Using paraffin heaters to provide heat and carbon dioxide
  • Applying fertilizers to ensure adequate nutrients
  • Using pesticides to control pests and pathogens
• Anaerobic respiration in plants and yeast

  • Glucose is converted to ethanol and carbon dioxide instead of lactic acid
  • In yeast, this process is called fermentation
  • Used to make bread, beer, and wine