Energy for Biological Processes

• What is photosynthesis?


  Energy in the form of sunlight is used to build complex molecules, such as glucose, with the light energy being transformed into chemical energy and trapped in the bonds of the complex organic molecules produced.
• What are autotrophic organisms?

  Organisms that can produce their own food through photosynthesis.
• What are heterotrophic organisms?

  Organisms that obtain their energy by consuming other organisms.
• What is similar about the following steps for both autotrophic and heterotrophic organisms?

  They both break down these complex organic molecules they have made or consumed through respiration to release the energy they require for metabolic processes.
• What is the equation for photosynthesis?

  6CO2 + 6H2O -> C6H12O6 + 6O2

  carbon dioxide + water = glucose + oxygen
• What are chloroplasts?


  Organelles found in plant cells that are responsible for photosynthesis, consisting of a network of membranes that provide a large surface area for light absorption.
• What are the structures of a chloroplast?

  Thylakoids, stroma, and grana.
• What are thylakoids?


  These are membrane bound flattened sacs that contain a pigment called chlorophyll, that absorbs light.
• What are stroma?


  This is the gel like fluid within the chloroplasts that contain enzymes responsible for the catalysing of reactions involved in photosynthesis, specifically the light independent stage.
• What is the grana?

  Stacks of thylakoids in chloroplasts, forming a basic structural unit.
• What connects each thylakoid to form grana?

  Lamellae, which are membranous channels.
• What other structures are present within a chloroplast?

  DNA, inner and outer membrane, starch grain.
• What is the purpose of the inner and outer membrane?

  It forms a chloroplast envelope, with the inner being permeable to a range of ions and small molecules, and the outer being permeable to a more selective range, containing transport proteins that only allow certain molecules and ions to enter or leave.
• What is the purpose of starch grain?

  Energy storage, as sugars formed during photosynthesis are stored as starch inside the starch grain.
• What is chlorophyll?


  The pigment of photosynthesis, with pigments absorbing specific wavelengths of light and reflecting others; with the primary pigment being chlorophyll a.
• What causes the varying colours and shades of leaves?

  Different combinations of pigments.
• What are the two pigment groups of photosynthesis?

  Chlorophyll and carotenoids.
• What are the two chlorophyll pigments?

  Chlorophyll a and chlorophyll b.
• What are the two carotenoids pigments?

  Beta-carotene and xanthophyll.
• What wavelengths do chlorophylls absorb?

  Blue, violet, and red regions of the light spectrum.
• What wavelengths do carotenoids absorb?

  Blue and violet regions of the light spectrum.
• What do pigments do?

  They absorb light and transfer the energy to electrons, with energy being passed through each pigment until it reaches the primary pigment.
• What are the two photosystems?

  Photosystem I and Photosystem II, both consisting of a light harvesting system, and a reaction centre.
• What are photosystems?


  Clusters of pigments in the thylakoid membrane that absorb and harvest light energy of different wavelengths during photosynthesis, and transfer this energy to the primary pigment located in the reaction centre.
• What are the max wavelengths of absorption for these two photosystems?

  Photosystem I: 700 nm Photosystem II: 680 nm
• What are the two stages of photosynthesis?

  Light dependent and light independent stage.
• Where does the light dependent stage occur?

  Thylakoid membrane of grana.
• Where does the light independent stage occur?

  Stroma.
• What does the light dependent stage involve?

  Cyclic, and non cyclic photophosphorylation.
• What is the light dependent stage of photosynthesis?

  This is when chlorophyll absorbs light energy, exciting electrons to higher energy levels, causing them to leave the chlorophyll and enter the electrons transport chain, generating NADPH and ATP.
• What photosystems does non cyclic involve use of?


  Photosystem I and photosystem II.
• What occurs in non cyclic phosphorylation part one?

  1. Light energy is absorbed by PSII and passed to the primary pigment of PSII, chlorophyll a.
  2. Two electrons from the primary pigment become excited, via photoionization, reaching a higher energy level and leaving the chlorophyll molecule.
  3. They enter the electron transport chain, releasing energy as they pass through it by oxidising and reducing the electron carrier proteins that act as electron acceptors.
  4. This energy is used to allow hydrogen ions to pass through the proton pump via active transport, creating an electrochemical gradient.
• What happens in non cyclic phosphorylation part two?


  1. Excited electrons from PSI are then released from its reaction centre into another electron transport chain.
  2. The build up of hydrogen ions in the thylakoid lumen causes them to move through the ATP synthase molecule via facilitated diffusion, back into the stroma.
  3. This movement of hydrogen ions drives the production of ATP from ADP and a phosphate, with the hydrogen ions being accepted by coenzyme NAPD along with an electron from PSI, to produce NADPH.
• What is this NADPH later used for?

  It later provides the hydrogen or reducing power in the production of organic molecules, such as glucose, in the light independent stage.
• What are the removed electrons from PSII replaced with during non cyclic phosphorylation?

  Electrons produced from photolysis.
• What are the removed electrons from PSI replaced with during non cyclic phosphorylation?

  Electrons that have just travelled along the previous electron transport chain after being released from PSII, making them de-energised.
• What is photolysis?


  The process of water molecules being broken down using light energy, into hydrogen ions, electrons, and oxygen molecules, making water a raw material of photosynthesis.
• What is present in PSII that catalyses photolysis?

  The oxygen evolving complex.
• What happens to the hydrogen ions produced in photolysis?

  They are released into the thylakoid lumen, furthering the electrochemical gradient and joining the other hydrogen ions in moving through the ATP synthase molecule into the stroma, where they can then combine with NADP and an electron from PSI to form NADPH.
• What happens to the oxygen produced in photolysis?


  It is discarded as waste.