Paper 1

• Aerobic respiration

  An exothermic reaction in which glucose reacts with oxygen to release energy which can be used by cells
• Aerobic respiration

  Glucose + oxygen → carbon dioxide + water (+energy)
• Aerobic respiration (symbol)

  C6H12O6 + 6O2 → 6CO2 + 6H2O (+energy)
• Where aerobic respiration takes place

  In the mitochondria
• Why organisms require the energy released by respiration

  • Synthesis of larger molecules
  • Muscle contraction
  • Maintenance of body temperature
  • Active transport
• Anaerobic respiration

  An exothermic reaction in which glucose is broken down to release energy in the absence of oxygen
• Anaerobic respiration

  Glucose → lactic acid (+energy)
• Anaerobic respiration is less efficient than aerobic respiration because glucose is not completely broken down, so less energy is transferred
• Anaerobic respiration can lead to muscle fatigue because lactic acid (the product) builds up in muscles, preventing efficient contraction
• Oxygen debt

  The amount of oxygen needed to convert lactic acid into back into glucose after anaerobic respiration
• Fermentation

  A type of anaerobic respiration that occurs in yeast cells
• Fermentation

  Glucose → ethanol + carbon dioxide (+energy)
• The fermentation reaction is important because it is used in the production of bread and alcoholic drinks
• Differences between aerobic and anaerobic respiration

  • Aerobic requires oxygen; anaerobic does not
  • Aerobic produces CO2 and water; anaerobic produces lactic acid or ethanol + CO2
  • Aerobic transfers a greater amount of energy
• How muscles store glucose

  As glycogen
• Changes that take place when muscular activity increases in the body

  • Heart rate increases and arteries dilate - increases flow of oxygenated blood to muscles
  • Breathing rate increases and breathing is deeper - increases the rate of gaseous exchange
  • Stored glycogen is converted back into glucose
• Blood flow through the muscles transports lactic acid to the liver, where it is oxidised back to glucose
• Metabolism

  The sum of all the reactions that take place in a cell or an organism
• Cells use the energy transferred by respiration to continuously carry out enzyme-controlled processes which lead to the synthesis of new molecules
• Examples of metabolic reactions

  • Glucose into starch/glycogen/cellulose
  • Glycerol and fatty acids into lipids
  • Glucose and nitrate ions into amino acids
  • Photosynthesis
  • Respiration
  • Breakdown of excess proteins into urea
• Photosynthesis

  The process by which plants synthesise glucose using light energy from the Sun. Light energy is converted into chemical energy.
• Where photosynthesis takes place

  Within chloroplasts in leaf palisade cells. They contain chlorophyll, a pigment which absorbs light energy.
• Photosynthesis (word)

  carbon dioxide + water → glucose + oxygen
• Photosynthesis (symbol)

  6CO2 + 6H2O → C6H12O6 + 6O2
• Photosynthesis is an endothermic reaction because energy is transferred from the environment to chloroplasts by light
• You can show that a plant gives off oxygen during photosynthesis by collecting gas bubbles produced by a water plant (e.g. Elodea) and testing that the gas relight a glowing splint
• Leaf adaptations which maximise the rate of photosynthesis

  • Broad leaves - maximise surface area
  • Thin leaves - short diffusion distance
  • Chlorophyll present - trap light energy
  • Veins - transport water to leaves via xylem, remove photosynthesis products via phloem
  • Air spaces - allow CO2 to enter and O2 to leave
  • Guard cells - control opening of stomata for gaseous exchange and prevent water loss
• Factors that affect the rate of photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration
  • Amount of chlorophyll
• Increasing the temperature increases the rate of photosynthesis as the kinetic energy of particles is increased, but the rate decreases past a certain temperature as enzymes become denatured
• Increasing the light intensity increases the rate of photosynthesis until another factor becomes limiting
• Increasing the carbon dioxide concentration increases the rate of photosynthesis (until another factor becomes limiting) as CO2 is required to make glucose
• Decreasing the amount of chlorophyll (e.g. due to a lack of magnesium) decreases the rate of photosynthesis as chlorophyll is required to absorb light energy
• Limiting factor

  An environmental factor which can restrict the rate of photosynthesis e.g. light intensity
• Calculating the rate of photosynthesis by measuring oxygen production

  1. Set up bubble potometer apparatus (pondweed in a sealed tube of water, attached to a capillary tube and a gas syringe)

  2. Oxygen gas produced causes the bubble in the capillary tube to move. The distance moved by the bubble is used to calculate the volume of oxygen produced
• Limiting factor

  An environmental factor which can restrict the rate of photosynthesis eg. light intensity
• Calculating the rate of photosynthesis by measuring oxygen production

  1. Set up bubble potometer apparatus (pondweed in a sealed tube of water, attached to a capillary tube and a gas syringe)

  2. Oxygen gas produced causes the bubble in the capillary tube to move

  3. The distance moved by the bubble is used to calculate the volume of oxygen produced
• Farmers use knowledge of limiting factors

  To control temperature, light intensity and CO2 concentration to achieve the fastest possible rate of photosynthesis, leading to a greater yield
• Inverse square law

  Light intensity ∝ 1 / distance^2
• Uses of glucose produced during photosynthesis

  • Respiration
  • Starch for storage
  • Cellulose for strength
  • Amino acid and protein synthesis (combined with nitrates)
  • Lipids for energy storage in seeds
• Aphids

  • Use their sharp mouthparts to extract sap from the plant phloem, weakening the plant
  • They are also vectors who can transfer pathogens from diseased plants to healthy plants