Bioenergetics

• Photosynthesis

  A chemical reaction in which energy is transferred from the environment (light from the Sun) to the leaves of a plant. It is an endothermic reaction.
• Chlorophyll

  • The green pigment in chloroplasts in the leaves that absorbs the light energy
• Leaves

  • Well adapted to increase the rate of photosynthesis when needed
• Carbon dioxide is used in photosynthesis
• Limiting factor is anything that limits the rate of a process
• Limiting factors for photosynthesis

  • Temperature
  • Carbon dioxide concentration
  • Light intensity
  • Amount of chlorophyll
• As temperature increases

  The rate of photosynthesis increases, up to an optimal temperature, then decreases as enzymes are denatured
• As carbon dioxide concentration increases

  The rate of photosynthesis increases, until another factor becomes limiting
• As light intensity increases

  The rate of photosynthesis increases, until another factor becomes limiting
• Photosynthesis will stop if there is little or no light
• Inverse square law

  As the distance of a light source from a plant increases, the light intensity decreases in inverse proportion to the square of the distance
• If you double the distance between a light source and a plant, light intensity falls by three quarters
• Commercial greenhouses

  • Control limiting factors to get the highest possible rates of photosynthesis to grow plants quickly or produce high yields, whilst still making a profit
• Uses of glucose produced in photosynthesis

  • Convert into insoluble starch for storage
  • Use for respiration to produce energy
  • Produce cellulose to strengthen cell walls
  • Produce fat or oil (lipids) for storage
  • Produce amino acids for protein synthesis (plants also need nitrate ions from the soil for this)
• Inverse square law

  The relationship between light intensity and distance that is not linear, but varies in inverse proportion to the square of the distance
• Limiting factor


  Anything that limits the rate of a process
• Photosynthesis


  The chemical reaction in which energy is transferred from light to the leaves of a plant, producing glucose
• Cellular respiration

  An exothermic reaction that occurs continuously in the mitochondria of living cells to supply the cells with energy
• Cellular respiration

  • Needed for all living processes, including chemical reactions to build larger molecules, muscle contraction for movement, and keeping warm
• Aerobic respiration

  Respiration that uses oxygen
• Anaerobic respiration

  Respiration that occurs without oxygen
• Aerobic respiration

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

  Glucose → lactic acid
• Anaerobic respiration in plant and yeast cells

  Glucose → ethanol + carbon dioxide
• Fermentation

  Anaerobic respiration in yeast cells
• The products of fermentation are important in the manufacturing of bread and alcoholic drinks
• Typical plant cell

  • Cell wall, chloroplast, cytoplasm, nucleus, mitochondrion, cell membrane
• You need to learn the balanced symbol equations for the different types of respiration as well as the word equations
• Key terms


  • aerobic
  • anaerobic
  • exothermic
  • fermentation
  • lactic acid
• During exercise

  Heart rate, breathing rate, and breath volume all increase to supply the muscles with more oxygenated blood
• If oxygen is insufficient

  Anaerobic respiration takes place instead, leading to the build-up of lactic acid
• During long periods of vigorous exercise

  Muscles become fatigued and stop contracting efficiently due to the build-up of lactic acid
• After exercise

  Oxygen debt is the amount of oxygen needed to react with the lactic acid to remove it from cells
• Removal of lactic acid

  Lactic acid in the muscles is transported to the liver in the blood, where it is converted back to glucose
• Metabolism

  The sum of all the reactions in a cell or the body, using the energy released by respiration to produce new molecules
• Metabolic processes

  • Synthesis and breakdown of carbohydrates, proteins, and lipids