Bioenergetics

• Explain how the process of photosynthesis works and why it is important for life on Earth.

  (6 marks)

  • Photosynthesis is the process by which plants use light energy to produce food.
  • It occurs in the chloroplasts of plant cells, using the green pigment chlorophyll.
  • The reaction involves carbon dioxide (from the air) and water (from the soil), producing glucose (a sugar) and oxygen.
  • The equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
  • Photosynthesis is essential for life because it provides the basis of food chains (producing glucose) and releases oxygen into the atmosphere.
  • Plants use glucose for growth and as an energy source for respiration.
  • Photosynthesis helps regulate the levels of carbon dioxide and oxygen in Earth’s atmosphere.
• Describe the factors that affect the rate of photosynthesis in plants.

  (6 marks)

  • Light intensity: The rate of photosynthesis increases as the light intensity increases, up to a certain point.
  • Carbon dioxide concentration: Higher concentrations of carbon dioxide can increase the rate of photosynthesis.
  • Temperature: Photosynthesis is faster at optimal temperatures (usually between 20°C-30°C). Temperatures too high or too low can slow down the process.
  • Chlorophyll concentration: The amount of chlorophyll in plant cells affects the rate of photosynthesis, as more chlorophyll allows more light absorption.
  • Water availability: Adequate water is necessary for photosynthesis, as it is one of the raw materials in the process.
• Explain the difference between aerobic and anaerobic respiration in living organisms.

  (6 marks)

  • Aerobic respiration occurs in the presence of oxygen and involves the complete breakdown of glucose to produce energy.
  • The products are carbon dioxide and water.
  • The equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.
  • Anaerobic respiration occurs in the absence of oxygen and involves the incomplete breakdown of glucose.
  • In animals, it produces lactic acid and energy.
  • The equation for animal cells is: C₆H₁₂O₆ → 2C₃H₆O₃ + energy.
  • In yeast and some plant cells, it produces ethanol and carbon dioxide.
  • Anaerobic respiration produces less energy than aerobic respiration because glucose is not fully broken down.
• Explain how exercise affects the rate of respiration in humans.

  (6 marks)

  • During exercise, muscles require more energy to contract.
  • The body responds by increasing aerobic respiration, which provides more energy.
  • The heart rate and breathing rate increase to supply more oxygen to muscles and remove carbon dioxide.
  • If oxygen supply is insufficient for the demands of exercise, anaerobic respiration occurs, leading to the production of lactic acid.
  • After exercise, the body continues to use oxygen to break down lactic acid in a process called oxygen debt.
• Describe the role of enzymes in metabolism.

  (6 marks)

  • Enzymes are biological catalysts that speed up chemical reactions in the body, including those involved in metabolism.
  • They are specific to the reactions they catalyse due to their active site shape.
  • Enzymes in metabolic processes can break down molecules (e.g., digestion) or build larger molecules from smaller ones (e.g., protein synthesis).
  • Respiration is an example of a metabolic process that involves enzymes to help break down glucose for energy.
  • Enzymes work best at an optimal temperature and pH, and their activity can be influenced by temperature and concentration of substrates.
• Explain why anaerobic respiration in humans results in muscle fatigue.

  (6 marks)

  • During intense exercise, muscles require more energy than aerobic respiration can provide, so they switch to anaerobic respiration.
  • Anaerobic respiration produces lactic acid as a byproduct, which builds up in the muscles.
  • The accumulation of lactic acid lowers the pH in the muscles, leading to a decrease in enzyme efficiency.
  • As a result, muscles become fatigued and are less able to contract effectively, causing muscle cramps.
  • After exercise, the body requires extra oxygen to convert lactic acid back into pyruvate, which can then enter the aerobic respiration pathway.
• What is the word equation for aerobic respiration?

  (1 mark)

  Glucose + Oxygen → Carbon Dioxide + Water + Energy.
• Explain how temperature affects the rate of photosynthesis.

  (4 marks)

  • As temperature increases, the rate of photosynthesis generally increases because the enzymes involved in photosynthesis work faster.
  • However, at high temperatures, the enzymes may become denatured, which slows down or stops the process.
  • The optimal temperature for photosynthesis is typically between 20°C and 30°C.
  • If the temperature becomes too high, photosynthesis will decrease because the enzymes lose their shape and cannot work effectively.
• Describe how plants use the glucose produced in photosynthesis.

  (4 marks)

  • Glucose produced during photosynthesis is used for respiration, providing energy for the plant’s growth, reproduction, and repair.
  • Some glucose is converted into starch for storage in roots, stems, or leaves.
  • Glucose is also used to make cellulose, which strengthens the plant cell wall.
  • Additionally, glucose is used to produce proteins through the process of amino acid synthesis.
• How does the body respond to exercise by increasing the rate of respiration?

  (4 marks)

  • During exercise, the muscles need more energy, so the rate of aerobic respiration increases to produce more ATP (energy).
  • The body increases heart rate and breathing rate to deliver more oxygen to the muscles and remove carbon dioxide more quickly.
  • If the demand for energy exceeds oxygen supply, anaerobic respiration occurs, producing lactic acid.
  • After exercise, the body continues to use oxygen to break down the lactic acid in a process called oxygen debt.
• Explain the difference between aerobic and anaerobic respiration in terms of energy release.

  (4 marks)

  • Aerobic respiration occurs in the presence of oxygen and produces a large amount of energy, as glucose is completely broken down into carbon dioxide and water.
  • Anaerobic respiration occurs in the absence of oxygen and releases less energy because glucose is only partially broken down, producing lactic acid (in animals) or ethanol and carbon dioxide (in yeast).
  • Aerobic respiration releases more energy than anaerobic respiration.
  • Anaerobic respiration is less efficient in terms of energy production.
• How do environmental factors such as light intensity and carbon dioxide concentration affect the rate of photosynthesis?

  (4 marks)

  • Light intensity: As light intensity increases, the rate of photosynthesis also increases, up to a certain point, as more light is available for the plant to absorb.
  • Carbon dioxide concentration: Higher carbon dioxide levels can increase the rate of photosynthesis, as CO₂ is one of the key raw materials for the process.
  • Both factors have a limit beyond which increasing them further will not increase the rate of photosynthesis.
  • Temperature also plays a role, and very high or low temperatures can slow down photosynthesis.