photosynthesis

• Where do the light-dependent reactions occur in plants?

  In the thylakoids of chloroplasts
• Where do the light-independent reactions occur in plants?

  In the stroma of chloroplasts
• What is the role of light in photoionisation?

  Chlorophyll absorbs energy from photons, exciting electrons to a higher energy level
• What are the two main stages involved in ATP production in the light-dependent reaction?

  Electron transfer chain and chemiosmosis
• What happens in the electron transfer chain (ETC)?

  Electrons move down carrier proteins in the thylakoid membrane and undergo redox reactions, releasing energy
• How is a proton concentration gradient established during chemiosmosis?

  Energy from the ETC is used to actively transport H+ ions from the stroma into the thylakoid space
• How does chemiosmosis produce ATP in the light-dependent stage?

  H+ ions move down their concentration gradient through ATP synthase, catalyzing the formation of ATP
• What is the role of light in photolysis?

  Light energy splits water molecules into H+ ions, electrons, and oxygen
• What happens to the products of the photolysis of water?

  H+ ions reduce NADP, electrons replace those lost from chlorophyll, and O2 is released as a waste gas
• How is reduced NADP produced in the light-dependent reaction?

  NADP + 2H+ + 2e- → reduced NADP, catalyzed by dehydrogenase enzymes in the stroma
• Where do the H+ ions and electrons used to reduce NADP come from?

  H+ ions come from the photolysis of water, and electrons come from the electron transfer chain
• What are the three main stages in the Calvin cycle?

  Carbon fixation, reduction, and regeneration
• What happens during carbon fixation in the Calvin cycle?

  CO2 reacts with ribulose bisphosphate (RuBP) to form an unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)
• What happens during reduction in the Calvin cycle?

  2x GP are reduced to 2x triose phosphate (TP) using 2x reduced NADP and 2x ATP, forming 2x NADP and 2x ADP
• How does the light-independent reaction produce useful organic substances?

  One carbon atom leaves the cycle, converting some TP into useful organic molecules
• What happens during regeneration in the Calvin cycle?

  After one carbon leaves the cycle, RuP forms, and RuBP is regenerated from RuP using one ATP, forming one ADP
• What is the sequence of events in the light-independent reaction (Calvin cycle)?

  1. Carbon fixation
  2. Reduction
  3. Regeneration
• What are the roles of ATP and reduced NADP in the light-independent reaction?

  • ATP: reduction of GP to TP and provides phosphate to convert RuP into RuBP
  • Reduced NADP: coenzyme that transports electrons for the reduction of GP to TP

  
• How many carbon atoms are in RuBP, GP, and TP?

  RuBP has 5 carbon atoms, GP has 3, and TP has 3
• Describe the structure of a chloroplast.

  • Usually disc-shaped
  • Double membrane (envelope)
  • Thylakoids: flattened discs stack to form grana
  • Intergranal lamellae: tubular extensions attach thylakoids in adjacent grana
  • Stroma: fluid-filled matrix
• How does the structure of the chloroplast maximize the rate of the light-dependent reaction?

  • ATP synthase channels within granal membrane
  • Large surface area of thylakoid membrane for ETC
  • Photosystems position chlorophyll for maximum light absorption

  
• How does the structure of the chloroplast maximize the rate of the light-independent reaction?

  • Own DNA and ribosomes for enzyme synthesis (e.g., rubisco)
  • High concentration of enzymes and substrates in stroma
• What is a limiting factor?


  A factor that determines the maximum rate of a reaction, even if other factors become more favorable
• Name four environmental factors that can limit the rate of photosynthesis.

  Light intensity, CO2 levels, temperature, and mineral/magnesium levels
• What are some common agricultural practices used to overcome the effect of limiting factors in photosynthesis?

  • Artificial light, especially at night
  • Artificial heating
  • Addition of CO2 to greenhouse atmosphere

  
• Why do farmers try to overcome the effect of limiting factors?

  To increase yield while balancing additional costs with profit
• How could a student investigate the effect of a named variable on the rate of photosynthesis?

  By measuring the rate of O2 production or CO2 consumption using a potometer
• What is the purpose and principle of paper chromatography?

  To separate molecules in a mixture based on their relative attraction to the mobile phase and stationary phase
• Outline a method for extracting photosynthetic pigments.

  Grind a leaf with an extraction solvent, such as propanone, using a pestle and mortar
• How can paper chromatography be used to separate photosynthetic pigments?

  1. Spot pigment extract onto pencil 'start line' on chromatography paper
  2. Place paper in solvent (origin above solvent level)
  3. Allow solvent to run until it almost touches the other end of the paper

  
• What are Rf values and how can they be calculated?

  Rf values are ratios that compare how far molecules have moved; calculated as distance from origin to pigment spot / distance from origin to solvent front

  
• What is the primary function of photosynthesis in plants?

  To produce glucose using light energy
• What are the reactants required for photosynthesis?

  Water and carbon dioxide
• What are the products of photosynthesis?

  Glucose and oxygen
• What are the two stages of photosynthesis?

  • Light dependent stage
  • Light independent stage
• What factors determine the rate of photosynthesis?

  Carbon dioxide concentration, light intensity, and temperature
• Where does photosynthesis occur in plant cells?

  In chloroplasts
• How are chloroplasts adapted for photosynthesis?

  • Contains stacks of thylakoid membranes (grana) for large surface area
  • Network of proteins holds chlorophyll for maximum light absorption
  • Granal membrane has ATP synthase channels and is selectively permeable
  • Contains DNA and ribosomes for protein synthesis
• What happens to chlorophyll molecules when photons of light hit them in the light dependent reaction?

  Electrons become excited, a process called photoionisation
• What is photolysis in the context of photosynthesis?

  The splitting of water using light