Topic 4 - Bioenergetics

• What is photosynthesis?


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

  Within chloroplasts in leaf palisade cells. They contain chlorophyll, a pigment which absorbs light energy.
• State the equations for photosynthesis

  (word and symbol)

  Word: carbon dioxide + water → glucose + oxygen

  
  

  Symbol: 6CO2 + 6H2O → C6H12O6 + 6O2
• Is photosynthesis an endothermic or exothermic reaction, and why?

  Endothermic - energy is transferred from the environment to chloroplasts by light.
• How can you show that a plant gives off oxygen during photosynthesis?

  Using a water plant, collect gas bubbles produced during photosynthesis. The gas will relight a glowing splint as it contains oxygen.

  
• Give examples of 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.
• What are the four main factors that affect the rate of photosynthesis?

  ● Temperature

  ● Light intensity

  ● Carbon dioxide concentration

  ● Amount of chlorophyll
• How does temperature affect the rate of photosynthesis?

  Increasing the temperature increases the rate of photosynthesis as the kinetic energy of particles is increased. The rate decreases past a certain temperature as enzymes become denatured.
• How does light intensity affect the rate of photosynthesis?

  Increasing the light intensity increases the rate of photosynthesis until another factor becomes limiting.
• How does carbon dioxide concentration affect the rate of photosynthesis?

  Increasing the carbon dioxide concentration increases the rate of photosynthesis (until another factor becomes limiting) as CO2 is required to make glucose.
• How does the amount of chlorophyll affect the rate of photosynthesis?

  Decreasing the amount of chlorophyll (eg. due to a lack of magnesium) decreases the rate of photosynthesis as chlorophyll is required to absorb light energy.
• What is a limiting factor?

  An environmental factor which can restrict the rate of photosynthesis eg. light intensity.
• Explain how you can calculate the rate of photosynthesis by measuring oxygen production

  ● Set up bubble potometer apparatus (pondweed in a

  sealed tube of water, attached to a capillary tube and a

  gas syringe).

  ● 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.
• How can farmers use their knowledge of limiting factors to increase their profits?

  They can control temperature, light intensity and CO2 concentration to achieve the fastest possible rate of photosynthesis, leading to a greater yield.
• State 5 uses of the 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
• What is aerobic respiration?

  An exothermic reaction in which glucose reacts with oxygen to release energy which can be used by cells.
• What are the equations for aerobic respiration? (word and symbol)

  Glucose + oxygen → carbon dioxide + water

  
  

  C6H12O6 + 6O2 → 6CO2 + 6H2O
• Where does aerobic respiration take place?

  mitochondria
• Why do organisms require the energy released by respiration?

  ● Synthesis of larger molecules

  ● Muscle contraction

  ● Maintenance of body temperature

  ● Active transport
• What is anaerobic respiration?

  An exothermic reaction in which glucose is broken down to release energy in the absence of oxygen.
• What is the equation for anaerobic respiration?

  glucose -> lactic acid
• Why is anaerobic respiration less efficient than aerobic respiration?

  Glucose is not completely broken down, so less energy is transferred.
• Why can anaerobic respiration lead to muscle fatigue?

  Lactic acid (product of anaerobic respiration) builds up in muscles, preventing efficient contraction.
• What is an oxygen debt?

  The amount of oxygen needed to convert lactic acid into back into glucose after anaerobic respiration.
• What is fermentation?


  A type of anaerobic respiration that occurs in yeast cells.
• What is the equation for fermentation?

  Glucose → ethanol + carbon dioxide
• Why is the fermentation reaction important?

  It is used in the production of bread and alcoholic drinks.
• What are the 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 do muscles store glucose?

  as glycogen
• What changes 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.
• How is lactic acid transported away from the muscles?

  Blood flow through the muscles transports lactic acid to the liver, where it is oxidised back to glucose.
• How do cells use the energy transferred by respiration?


  To continuously carry out enzyme-controlled processes which lead to the synthesis of new molecules.
• Give 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