energy transfers

• What is the main topic of AQA A Level Biology Topic 5?

  Energy transfers in and between organisms
• 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 Calvin cycle?

  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 as enzymes denature due to the breaking of hydrogen bonds in their tertiary structure.

  
• How does light intensity affect the rate of photosynthesis?

  As light intensity increases, the rate of photosynthesis increases until another factor becomes limiting.

  
• What occurs in the light-dependent reaction as light intensity increases?

  More photoionisation of chlorophyll occurs, leading to increased production of ATP and reduced NADP.

  
• What happens when light intensity reaches a certain level?

  The rate of photosynthesis stops increasing due to another limiting factor, 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 another factor becomes limiting.

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

  More CO2 combines with RuBP to form GP, leading to increased production of TP and organic substances.
• What occurs when CO2 concentration reaches a certain level?

  The rate of photosynthesis stops increasing due to another limiting factor, 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 & environmental).
• Why is it important to specify chlorophyll when discussing light absorption in photosynthesis?

  Chlorophyll specifically absorbs light energy, while chloroplasts are too vague.
• 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 passage of electrons down the electron transfer chain linked to energy release?

  The energy released as electrons pass along the ETC allows protons to be pumped into the thylakoid, creating a gradient for ATP production.

  
• What does GP stand for in photosynthesis?

  Glycerate 3-phosphate
• Why is it important to specify CO2 concentration when discussing limiting factors in photosynthesis?

  Specifying concentration is necessary to accurately identify CO2 as a limiting factor.

  
• Why must triose phosphate be written 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?

  • To investigate pigments isolated from leaves of different plants.
  • Examples include shade-tolerant and shade-intolerant plants or leaves of different colors.
• What is the first step in isolating pigments from a leaf using paper chromatography?

  Crush leaves with solvent to extract pigments.
• Why should the pencil line be drawn above the bottom of the chromatography paper?

  The pencil line should be above the solvent level to prevent pigments from dissolving into the solvent.
• What happens during chromatography as the solvent moves up the paper?

  The solvent carries dissolved pigments up the paper.
• 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?

  Measuring the center standardizes readings as pigments can spread out.
• Why might obtained Rf values be similar but not identical to published values?

  Different solvent, paper, or running conditions may affect Rf values.
• 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 distances vary.
• What is the focus of Required Practical 8 in photosynthesis?

  • Investigation into the effect of a named factor on the rate of dehydrogenase activity in chloroplast extracts.
• What role does the enzyme dehydrogenase play in photosynthesis?

  Dehydrogenase catalyses the reduction of NADP in the light-dependent reaction.

  
• How can the rate of dehydrogenase activity in chloroplast extracts be measured?

  By timing how long it takes for DCPIP to turn from blue to colorless in the presence of chloroplasts.
• What is the term for the fluid-filled space inside mitochondria?

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

  Oxidative phosphorylation

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

  Anaerobic respiration