exam questions

• Name the organelle that fixes carbon dioxide from the atmosphere (1) 

  -       Chloroplasts
• Where in the chloroplasts the light-dependant reactions take place (1) 

  Thylakoids (found in the grana)
• State the location of chlorophyll in a chloroplast (1)

  -       Thylakoid membrane/grana 
• In which part of the chloroplast does the light-independent reactions take place (1)

  -       Stroma 
• Explain the relationship between the structure and functions of a granum in photosynthesis (3) 

  -       Granum is formed from many layers of thylakoid membranes to increase surface area for absorbing light 

  -       As the thylakoid membranes contain chlorophyll to absorb light- for light dependant reaction 

  -       Electron carrier molecules in thylakoid membrane involved in ATP production
• describe the light independent reaction of photosynthesis (5) 

  • use of light energy to excite electrons in chlorophyll
  • photolysis of water to produce oxygen, electrons and hydrogen ions
  • electrons used in the ETC to replace those by by chlorophyll
  • generation of ATP/photophosphorylation
  • reduction of NADP
• Where does the light dependant stage take place? (1) 

  -       Thylakoids
• What are the products of the light dependant reaction (1) 

  -       Oxygen, reduced NADP, ATP
• Describe the light dependant reaction (5)- save my exams 

  • Light energy excites electrons+ raises electrons to a higher energy level
  • Electrons are passed along the electron transport chain AND release energy
  • (Energy is used to) pump hydrogen ions across the thylakoid membrane (which then diffuse back again via ATP synthase)
  • (Energy is used to) phosphorylate ADP / produce ATP from ADP and Pi
  • Light energy photolysis/splits water molecules into protons AND electrons AND oxygen
  • NADP is reduced / reduced NADP/NADPH is produced
• Aside from the general effect of cold temperatures on enzyme-controlled reactions, explain why extreme cold leads to a decrease in the rate of the light independent reactions (2) 

  -       There is less/no ATP being produced by the light-dependant reaction

  -       No reduced NADP from the light dependant reaction
• Describe how starch is formed from the products of the light independent reactions of photosynthesis (4) 

  -       1 carbon molecule from 2x GALP used to form glucose molecule, 6 cycles of the Calvin cycle for 1 glucose molecule 

  -       Glucose molecules join 1,4 glycosidic bonds and 1,6 for amylopectin only

  -       Occurs via a condensation reaction

  -       Producing amylose and amylopectin
• Explain why increase in C02 concentration affects the growth of plants in glasshouses (3) 

  -       Carbon dioxide is the limiting factor 

  -       Carbon is fixed with RuBP to produce GP and then into GALP

  -       Thus, more carbon dioxide means more glucose is being produced and amino acids 

  -       Which would lead to greater rate of growth
• Name 2 immediate products from the light dependant stage (2) 

  -       GALP and GP
• Describe the roles of the products of the light dependant reactions in the Calvin cycle (3) 

  -       ATP provides energy and reduced NAPH provides hydrogens for the reduction of GP into GALP 

  -       ATP also used in the regeneration of RuBP- converting GALP to RUBP
• Explain the importance of RUBISCO to the productivity of an ecosystem (2) 

  -       Fixes inorganic carbon/ CO2 (combines RuBP with CO2) 

  -       Allowing formation of organic molecules by the carbon cycle e.g., glucose 

  -       These organic molecules allow transfer of energy to next trophic level
• Explain how glucose can be used in the plant

  -       Can enter respiration to release energy 

  -       Can be converted into starch for storage 

  -       Can be converted into cellulose for cell wall structure 

  -       Can be converted into sucrose for transport
• A decrease in the activity of rubisco limits the rate of photosynthesis, why?  (2) 

  -       Less RuBP and C02 are combining 

  -       Less GP and GALP produced so no regeneration of RuBP
• Explain what is meant by fixation of carbon dioxide (3) 

  -       Removal of carbon dioxide from the air 

  -       Carbon atoms from carbon dioxide are incorporated into organic material 

  -       Catalysed by enzyme rubisco

  -       To build up plant’s biomass/cells/tissues