5. Energy transfers

• What are the two main stages of photosynthesis?

  • Light dependent reaction
  • Light independent reaction (Calvin cycle)

  
• What is photoionisation in the light-dependent reaction?

  Chlorophyll absorbs light energy, exciting its electrons to a higher energy level.
• What happens after photoionisation in the light-dependent reaction?

  Some energy from the released electrons is conserved in the production of ATP and reduced NADP.
• What is the chemiosmotic theory in the light-dependent reaction?

  1. Electrons move along the electron transfer chain, releasing energy.
  2. This energy pumps protons from the stroma into the thylakoid.
  3. Protons move back into the stroma via ATP synthase.
  4. Energy is used to join ADP and Pi to form ATP (photophosphorylation).
  5. NADP accepts a proton and an electron to become reduced NADP.

  
• What is photolysis of water in the light-dependent reaction?

  Water splits to produce protons, electrons, and oxygen.
• What is the first step of the light-independent reaction (Calvin cycle)?

  CO2 reacts with ribulose bisphosphate (RuBP), catalysed by the enzyme rubisco.
• What happens to glycerate 3-phosphate (GP) in the light-independent reaction?

  GP is reduced to triose phosphate (TP) using products from the light-dependent reaction.
• What are the outcomes of triose phosphate (TP) in the Calvin cycle?

  • Some TP is converted to useful organic substances (e.g., glucose).
  • Some TP is used to regenerate RuBP using energy from ATP.
• How does temperature affect the rate of photosynthesis?

  As temperature increases, the rate of photosynthesis increases until an optimum temperature is reached, after which it decreases.

  
• Why does the rate of photosynthesis increase with temperature up to a certain point?

  Enzymes like rubisco gain kinetic energy, leading to more enzyme-substrate complexes forming.

  
• What happens to the rate of photosynthesis above the optimum temperature?

  The rate decreases because enzymes denature as hydrogen bonds in their tertiary structure break.

  
• How does light intensity affect the rate of photosynthesis?

  As light intensity increases, the rate of photosynthesis increases until a certain point where it levels off due to other limiting factors.

  
• Why does the light-dependent reaction increase with light intensity?

  More light leads to more photoionisation of chlorophyll, resulting in more ATP and reduced NADP produced.

  
• What happens to the rate of photosynthesis above a certain light intensity?

  The rate stops increasing because another factor becomes limiting, such as temperature or CO2 concentration.

  
• How does CO2 concentration affect the rate of photosynthesis?

  As CO2 concentration increases, the rate of photosynthesis increases until a certain point where it levels off.

  
• What happens to glycerate 3-phosphate (GP) as CO2 concentration increases?

  More CO2 combines with RuBP to form GP, leading to more GP being reduced to TP.
• What happens to the rate of photosynthesis above a certain CO2 concentration?

  The rate stops increasing because another factor becomes limiting, such as temperature or light intensity.

  
• What is a key consideration when evaluating agricultural practices to overcome limiting factors in photosynthesis?

  • Agricultural practices should increase the rate of photosynthesis.
  • This leads to increased yield and more glucose for respiration.
  • Profit from extra yield should exceed costs (money and environmental).
• Why is it incorrect to say "Chloroplasts absorb light energy"?

  It is too vague; chlorophyll specifically absorbs light energy.
• What is the difference between NADP and NAD/FAD in photosynthesis and respiration?

  NADP is used in photosynthesis, while NAD and FAD are used in respiration.
• How is the energy released as electrons pass along the electron transfer chain (ETC) used?

  The energy allows protons to be pumped into the thylakoid, creating a gradient that drives ATP production via chemiosmosis.

  
• What does GP stand for in photosynthesis?

  Glycerate 3-phosphate
• What must be specified when referring to carbon dioxide as a limiting factor?

  The concentration of carbon dioxide must be specified.
• Why must triose phosphate be written out in full before using the abbreviation TP?

  TP is not an abbreviation recognized in the specification, so it must be written in full first.
• What is the purpose of chromatography in studying plant pigments?

  • Isolate pigments from leaves of different plants.
  • Compare pigments from shade-tolerant and shade-intolerant plants.
  • Analyze pigments of different colors.
• How are pigments isolated from a leaf using paper chromatography?

  Crush leaves with solvent to extract pigments, then apply to chromatography paper.
• Why should the origin line in chromatography be drawn in pencil rather than ink?

  Ink is soluble in solvent and would mix with pigments, affecting results.
• Why should the point of origin be above the level of the solvent in chromatography?

  To prevent pigments from running off the paper or dissolving into the solvent.
• Why might a pigment not move up the chromatography paper in one solvent?

  The pigment may be soluble in one solvent but insoluble in another.
• How is the Rf value calculated in chromatography?

  Rf value = distance moved by spot / distance moved by solvent front.
• Why should the solvent front be marked quickly after removing chromatography paper?

  Once the solvent evaporates, the solvent front becomes invisible.
• Why should the center of each pigment spot be measured in chromatography?

  To standardize readings as pigments can spread out, allowing for accurate comparisons.
• Why might obtained Rf values be similar but not identical to published values?

  Different solvent, paper, or running conditions may affect the Rf value.
• Why are Rf values used instead of distances moved by pigment spots?

  Rf values are constant for the same pigment and can be compared, while solvent and pigment move different distances.
• What is the role of the enzyme dehydrogenase in photosynthesis?

  It catalyses the reduction of NADP in the light-dependent reaction.
• What is the term for the fluid-filled space inside mitochondria?

  Chondrial matrix
• What is the process called that occurs in the inner mitochondrial membrane?

  Oxidative phosphorylation

  
• What type of respiration occurs in the absence of oxygen?

  Anaerobic respiration
• Where does glycolysis take place in the cell?

  In the cytoplasm
• What is the purpose of NAD regeneration in the cytoplasm?

  To allow glycolysis to continue