AQA biology topic 5 and 6

• Chlorophyll is a green pigment that is found embedded in the membranes of the grana
• Photoionisation


  1. Light hits a chlorophyll molecule

  2. Electron absorbs light energy and moves to a higher energy level

  3. Electron becomes excited
• Electron transfer chain


  1. Electron passes to a carrier protein in the membrane

  2. Electron passes through a series of protein carrier molecules in the membrane

  3. As electron moves down the chain, energy is lost

  4. ATPase makes ATP from ADP and Pi
• Photolysis


  1. Light energy splits water

  2. Produces oxygen

  3. Produces electrons to replace those lost by chlorophyll

  4. Produces H+ ions
• NADPH


  Reduced coenzyme formed when H+ ions join with electrons that have passed through the electron transfer chain
• Light-independent stage of photosynthesis

  1. Carbon dioxide joins with ribulose bisphosphate (RuBP)

  2. Resulting molecule splits to form two molecules of glycerate-3-phosphate (GP)

  3. GP is reduced to triose phosphate (TP) using NADPH and ATP

  4. TP can be used to regenerate RuBP or synthesise organic molecules

  
• Limiting factors


  • If any one factor is in short supply, it becomes a limiting factor
  • Only one factor can limit the rate of photosynthesis at one time
  • If a limiting factor is increased, the rate of photosynthesis increases
• Light intensity is the limiting factor in the part of the graph that slopes upwards
• When the graphs flatten off, another factor is limiting photosynthesis
• In graph D, the limiting factor must be temperature
• Rf value


  Ratio of the distance moved by a pigment to the distance moved by the solvent front
• Having several different pigments in the chloroplast, in addition to chlorophyll, provides an advantage to the plant
• Glycolysis


  1. Glucose is phosphorylated to glucose phosphate using ATP

  2. Glucose phosphate is broken down into two molecules of triose phosphate

  3. Triose phosphate is oxidised to form pyruvate, yielding reduced NAD and ATP

  
• Link reaction


  1. Pyruvate is converted to acetate

  2. Produces reduced NAD and releases carbon dioxide

  
• Krebs cycle


  1. Acetyl coenzyme A joins with a 4C compound to produce a 6C compound

  2. 6C compound is broken down to a 5C compound

  3. 5C compound is broken down into a 4C compound

  4. 4C compound combines with another acetyl coenzyme A

  5. Cycle continues, breaking down acetyl coenzyme A and producing reduced coenzymes and ATP

  
• Electron transfer chain


  1. Reduced coenzymes pass hydrogen to carrier proteins

  2. Protons pass through to space between inner and outer mitochondrial membrane

  3. Electrons pass through proteins in the chain

  4. Protons return through ATP synthase, producing ATP

  5. Protons and electrons recombine with oxygen to form water
• Anaerobic respiration


  Pyruvate is converted to lactate (in animals and some bacteria) or to ethanol and carbon dioxide (in plants and most microorganisms)

  
• If pyruvate was not converted in anaerobic conditions, NAD could not be recycled
• The yield of ATP is much higher in aerobic respiration compared to anaerobic respiration
• The gas being given off by the yeast is carbon dioxide
• Even with distilled water containing no respiratory substrate, some gas is given off by the yeast
• A control investigation with boiled yeast suspension should be included
• Glycolysis


  1. Glucose is broken down to two molecules of pyruvate, producing a small net gain of ATP and reduced coenzymes

  2. Takes place in the cytoplasm

  
• Link reaction


  1. Pyruvate is converted to acetyl coenzyme A, producing reduced coenzymes and carbon dioxide

  2. Takes place in the mitochondrial matrix

  
• Krebs cycle


  1. Acetyl coenzyme A is completely broken down, yielding carbon dioxide, ATP and reduced coenzymes

  2. Takes place in the mitochondrial matrix

  
• Electron transfer


  1. Hydrogen atoms from the reduced coenzymes split into protons and electrons

  2. Electrons pass through the electron transfer chain

  3. Protons pass through an ATP synthase molecule, producing ATP

  4. Oxygen is the final electron acceptor
• Anaerobic respiration


  Consists of glycolysis only, with pyruvate converted into lactate (in animals and some bacteria) or to ethanol and carbon dioxide (in plants and most microorganisms) to oxidise the reduced coenzymes, allowing glycolysis to continue

  
• The basis of almost all ecosystems is green plants. These absorb light energy and carbon dioxide and produce organic matter in photosynthesis.
• Biomass


  The total mass of organisms in a given area, measured in terms of carbon or dry mass of tissue per given area per given time
• The dry mass of grass in a field would be found by sampling a square metre at random, removing the grass including the roots, washing off soil, and weighing the dried grass to constant mass
• Calorimeter


  Apparatus used to measure the energy stored in biomass by burning a known dry mass of biological material inside the calorimeter and measuring the temperature rise of a known volume of water

  
• Gross primary production (GPP)


  The chemical energy stored in plant biomass
• Net primary production (NPP)

  The chemical energy stored in plant biomass after respiratory losses have been taken into account, available to primary consumers and decomposers
• Net production of consumers (N)

  Calculated as I - F - R, where I = chemical energy in ingested food, F = chemical energy lost to the environment in faeces and urine, and R = respiratory losses to the environment
• In agriculture, farmers may increase the efficiency of energy transfer by adopting various farming practices, such as rearing livestock indoors, to reduce energy losses in heat and movement
• Only up to 10% of chemical potential energy in primary consumers becomes chemical potential energy in secondary consumers, and only up to 10% of chemical potential energy in secondary consumers becomes chemical potential energy in tertiary consumers
• Only 2% of light energy becomes chemical potential energy in producers
• Food chains rarely have more than five trophic levels
• So little energy is transferred from one trophic level to the next because some of the light energy is the wrong wavelength for photosynthesis, some does not hit a chloroplast, some is converted to heat energy, and some is reflected or transmitted through the leaf

  
• Saprobionts are organisms, mainly fungi and bacteria, that secrete enzymes onto dead organic remains and digest the material, absorbing some of the nutrients