Photosynthesis

• Write out the overall chemical reactions for photosynthesis and respiration.

  Photosynthesis: 6CO2+6H2O -> C6H12O6 +6O2Respiration: C6H12O6+6O2 -> 6CO2 + 6H2O
• Describe the relationship between photosynthesis and respiration, and use this to explain the importance of photosynthesis for consumers as well as producers

  They are the reverse of each other. Photosynthesis is important for consumers as well as producers as it traps the energy from the sun to be transferred through the food chain.
• Use the concept of "bond energy" to explain why photosynthesis requires energy from the sun and stores energy whereas respiration releases energy that can be used to make ATP.


  Bonds require energy to be broken and give out energy when formed. Bonds in small inorganic molecules are strong and require lots of energy to break but give out lots of energy when they from. The bonds in larger organic molecules are weaker. This means a lot of energy is needed to break the bonds in CO2 and H2O for photosynthesis but little is given out when glucose forms. The reverse is true for respiration; it requires little energy to break the bonds in glucose but lots is given out as CO2 and H2O form.
• Draw, label and annotate a diagram of a chloroplast.

  
• Name the two main stages of photosynthesis and state where each occurs in a chloroplast.

  Light-dependent stage occurs within and across thylakoid membranesLight-independent stage occurs in the stroma
• Draw a diagram to outline the process of photosynthesis as two, linked, main stages (the light dependent stage and the light independent stage)

  
• Define the terms "photosynthetic pigment", "light harvesting system", "antennae complex", "reaction centre", and "photosystem"

  Photosynthetic pigment - a pigment that absorbs light energyLight harvesting system - a group of protein and chlorophyll molecules found in the thykaloid membranes of the chloroplasts in a plant cellAntennae complex - another name for light harvesting systemReaction centre - complex of proteins, pigments and cofactors that execute the primary energy conversion reactions of photosynthesisPhotosystem - LHS and reaction centre collectively known as a photosystem. Biochemical mechanism in plants by which chlorophyll absorbs light energy for photosynthesis.
• Name the photosynthetic pigment in the reaction centre of a photosystem.

  Chlorophyll a
• Name 3 types of photosynthetic pigments found in the antennae complex

  Chlorophyll b, xanthophylls and carotenoids
• Explain why it is useful for photosynthetic organisms to have many different photosynthetic pigments.

  To absorb different wavelengths of light so maximise energy transferred to the reaction centre.
• Label and annotate an absorption spectrum graph to explain what it shows

  E.g.Chlorophyll absorbs red and blue but reflects green wavelengths

  
• Describe the purpose of chromatography

  Used to separate and identify substances
• Describe a step by step method for conducting thin layer chromatography to separate and identify photosynthetic pigments.

  Mobile phase is solution containing mixture of pigments. Stationary phase is a thin layer of silica gel applied to glass.
• State what "Rf" stands for in "Rf value".

  Retention factor
• Draw a diagram of a chromatogram showing how to calculate the Rf values of each spot.

  
• Explain how to use Rf values to identify the molecules present in a solution

  Rf values compared to a table of known values to identify components
• Explain what determines how far a particular molecule travels in chromatography

  Different solubilities and interactions with the stationary phase lead to different distances travelled and therefore different Rf values.
• Draw a diagram to summarise the light-dependent stage of photosynthesis and state where this occurs.

  Occurs within and across thylakoid membranes

  
• Name the two useful products, the waste product, and the requirements, of the light-dependent stage of photosynthesis.

  Produces reduced NADP, ATP and the waste product OxygenRequires Water and Sunlight
• Define the terms "oxidation" and "oxidised", and "reduction" and "reduced"

  Oxidation - removal of electrons (or hydrogen)Oxidised - having lost electronsReduction - gaining electronsReduced - having gained electrons
• Define the terms "phosphorylation", "photophosphorylation", "cyclic photophosphorylation", "non-cyclic photophosphorylation", and "photolysis"


  Phosphorylation - the addition of a phosphate group to a moleculePhotophosphorylation - the addition of a phosphate group to a molecule using light energyCyclic photophosphrylation - synthesis of ATP involving photosystem 1Non-cyclic photophosphorylation - the synthesis of ATP and reduced NADP involving photosystems 1 and 2Photolysis - the decomposition or separation of molecules using light
• Draw, label and annotate a diagram to show the process of cyclic phosphorylation

  Light energy converted to chemical energy in excited electrons which is used to phosphorylate ADP to ATP

  
• Draw, label and annotate a diagram to show the process of non-cyclic phosphorylation.

  Electrons do not cycle, they enter with water and leave in NADPH2

  
• Describe the process of photolysis and what the products of photolysis are used for.

  Water is split by light. Oxygen is lost. H+ ions join NADP to form NADPH2. Electrons pass into chain, eventually joining the H+ to complete the reduction of NADP to NADPH2.
• Draw a diagram to summarise the light-independent stage of photosynthesis and state where this occurs

  Occurs in the stroma

  
• Name the useful product of, the three requirements of, and the molecules that are returned to the light-dependent stage from, the light-independent stage of photosynthesis.

  Useful product: Triose phosphateRequirements: NADOH2, ATP and CO2The molecules ADP and NADP are returned to the light-dependent stage.
• Define the terms "RuBP", "RuBisCO", "GP", "TP", and "carbon fixation"

  RuBP - Ribulose bisphosphate - a 5 carbon compoundRuBisCO - Ribulose bisphosphate carboxylase - enzyme that catalyses the carbon fixationGP - glycerate 3-phosphate - 3 carbon moleculeTP - Triose phosphate - 3 carbon moleculeCarbon fixation - the incorporation of carbon into organic compounds by living organisms, chiefly by photosynthesis in green plants
• Draw, label and annotate a diagram to show the Calvin cycle.


  6CO2 are incorporated into the cycle by the enzyme rubisco catalysing the reaction with 6RuBP to from 12GP. These are reduced to TP by hydrogen from 12 NADPH2 and using energy from 12ATP.2TP now leave the cycle and are the net product. The remaining 10TP are converted into RuP, which are then phosphorylatted by a further 6ATP to reform 6RuBP and continue the cycle.

  
• Describe the roles of ATP and reduced NADP in the Calvin cycle.

  Both in the reduction of GP to TP.ATP also in the regeneration of RuBP.
• Explain how RuBP is regenerated in the Calvin cycle.

  TP is converted into RuP which is then phosphorylated by ATP to reform RuBP.
• Describe the uses of triose phosphate.

  To form other carbohydrates such as glucose as well as proteins, lipids and nucleic acids. It is the starting point of many organic synthesis reactions.
• Describe the process of photorespiration.

  Oxygen is a competitive inhibitor of RuBisCO. When CO2 levels are very low, phosphoglycolate is produced. This is a toxic 2 carbon compound and is converted to other organic molecules using ATP.

  
• Label and annotate an action spectrum graph to explain what it shows.

  
• Describe the difference between an absorption spectrum graph and an action spectrum graph.

  Absorption spectrum shows the absorbance of light at each wavelength of the pigments whereas an action spectrum shows the effectiveness of photosynthesis (the action).
• Define the term "limiting factor".

  Factor which limits the rate of a process.
• State 5 factors that affect the rate of photosynthesis.

  Light intensityCarbon dioxide concentrationTemperatureWater stressNumber of chloroplasts etc.
• Describe how light intensity, temperature and carbon dioxide concentration affect the rate of photosynthesis

  Light provides energy needed to excite electrons to reduce NADP and phosphorylate ADP, the products of the light dependent stage that are then needed in the light independent stage. If there is higher light intensity, more energy is provided and the rate of photosynthesis increases.Temperature affects the rate of enzyme controlled reactions. Increased temperature increases rate until an optimum, after which proteins denature and the rate decreases.CO2 needs to be fixed in the Calvin Cycle as a source of carbon to produce TP so as CO2 increases, rate of TP production can increase.
• Explain how graphs of the rate of photosynthesis under different environmental conditions can show what is limiting the rate of photosynthesis under a particular set of conditions

  If rate changes as the factor changes then the factor is a limiting factor. If graph plateaus then a different factor is limiting the rate.
• Explain how water stress limits the rate of photosynthesis but water availability itself is not considered to be a limiting factor.

  Stomata close to prevent water loss by transpiration when the plant is under water stress but when stomata are closed no CO2 can diffuse into the leaves for photosynthesis, reducing the rate of the light-independent reaction and eventually stopping photosynthesis. For water availability to limit photosynthesis there would have to be so little available that the plant would have long stopped photosynthesising from closing its stomata and is unlikely to survive these conditions without specific adaptations.
• Describe how the rate of photosynthesis can be measured.

  Measuring oxygen production - only possible for aquatic plants Count the bubbles or measure volume of gas in upturned cylinder or gas syringeMeasure uptake of CO2Use radioactive C14 and measure uptake of radioactivity