module 5 (photosynthesis )

• How are photosynthesis and respiration related?

  CO2 and H2O are raw materials for photosynthesis and products of respiration.
• What are the raw materials and products of respiration?

  O2 and glucose are the raw materials for respiration and products of photosynthesis.
• 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 with high enzyme & substrate concentration & own loop of DNA
• 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 photosynthetic pigments?

  They absorb different wavelengths of light to maximize the rate of photosynthesis.
• What are the two main groups of photosynthetic pigments?

  Primary pigments and accessory pigments.
• What is the primary pigment in photosynthesis?

  Chlorophyll.
• What are the accessory pigments in photosynthesis?

  Carotenoids (carotene and xanthophylls).
• Name the processes in the light-dependent reaction.

  • Photoionisation
  • Electron transfer chain
  • Chemiosmosis
  • Non-cyclic only: reduction of NADP, photolysis of water
• What is the role of light in photoionisation?

  Chlorophyll absorbs energy from photons, exciting electrons to a higher energy level.
• What happens in the electron transfer chain (ETC)?

  Electrons move down carrier proteins in the thylakoid membrane, undergoing redox reactions that release energy.
• 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.
• Describe non-cyclic photophosphorylation.

  • Uses Photosystems I & II
  • Excited electrons enter ETC to produce ATP
  • NADP acts as final electron acceptor and is reduced
  • Water is photolysed to replace lost electrons
  • Purpose: produce ATP & reduced NADP for the Calvin cycle
• Describe cyclic photophosphorylation.

  • Uses only Photosystem I
  • Excited electrons enter ETC to produce ATP and return to photosystem
  • No reduction of NADP and no water needed
  • Purpose: produce additional ATP for energy demands
• What happens in photolysis of water?

  Light energy splits water molecules into H+, e-, and O2.
• What happens to the products of the photolysis of water?

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

  In the stroma, NADP is reduced by H+ ions and electrons from the ETC.
• Name the 3 main stages in the light-independent reaction.

  1. Carbon fixation
  2. Reduction
  3. Regeneration
• What happens during carbon fixation?

  CO2 reacts with RuBP, catalyzed by RuBisCo, forming an unstable 6C intermediate that breaks down into 2 GP.
• What happens during reduction in the light-independent reaction?

  2 GP are reduced to 2 TP using reduced NADP and ATP, forming NADP and ADP.
• Outline the roles of TP from the light-independent reaction.

  • Raw material for producing monosaccharides, amino acids, and other molecules
  • Involved in regenerating RuBP using ATP
• Outline the sequence of events in the light-independent reaction.

  1. Carbon fixation
  2. Reduction of GP to TP
  3. Regeneration of RuBP
• State the number of carbon atoms in RuBP, GP, and GALP.

  RuBP: 5, GP: 3, GALP: 3.
• Define ‘limiting factor’.

  A factor that determines the maximum rate of a reaction, even if other factors become more favorable.
• Name 4 environmental factors that can limit the rate of photosynthesis.

  • Light intensity
  • CO2 levels
  • Temperature
  • Mineral/magnesium levels
• How does light intensity affect the rate of photosynthesis?

  Low light intensity slows the light-dependent reaction, reducing ATP and NADPH production.
• Describe the implications of water stress.

  1. Abscisic acid binds to receptors on guard cells, opening Ca2+ channels.
  2. Other ion channels open, causing K+ to diffuse out.
  3. Water potential of guard cells becomes positive, leading to water loss.
  4. Guard cells become flaccid, closing stomata.
• State the purpose and principle of thin layer chromatography (TLC).

  TLC separates molecules based on their attraction to the mobile phase versus the stationary phase.
• Outline a method for extracting photosynthetic pigments.

  • Grind a leaf with an extraction solvent (e.g., propanone) using a pestle and mortar.
• Outline how TLC can be used to separate photosynthetic pigments.

  1. Spot pigment extract onto a pencil 'start line' on TLC paper.
  2. Place paper in solvent, ensuring the origin is above solvent level.
  3. Allow solvent to run until it almost touches the other end of the paper.