11 - Photosynthesis

• What is the advantage of a plant having multiple pigments?

  • The advantage of having multiple pigments is that a wider range of wavelengths of light is absorbed.
  • Therefore, more light energy is absorbed for the LDR (more photoionisation of chlorophyll)
• Where does the light-dependent reaction (LDR) occur?

  Thylakoid membrane
• What are the three key reactions in the LDR?

  • Photoionisation of chlorophyll
  • Photolysis
  • Chemiosmosis
• What is the symbol equation for photolysis?

  H20 --> 1/2 02 + 2e- + 2H+
• Describe photoionisation of chlorophyll

  1. Light energy is absorbed by the chlorophyll
  2. Electrons get excited, raising an energy level to leave the chlorophyll
  3. Chlorophyll has now been ionised by light
  4. Some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis
• What are the parts of the chloroplast?

  • Outer Membrane
  • Inner Membrane
  • Intermembrane Space
  • Stroma
  • Thylakoid (a stack is called a granum)
  • Lamella
  • Lumen

  
• Use the diagram to describe chemiosmosis in 4 key stages (PART 1)

  1. The electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane.
  2. As they move along, they release energy and some of the energy from electrons is used to pump the protons across chloroplast membranes.

  
• Use the diagram to describe chemiosmosis in 4 key stages (PART 2)

  
  

  3. An electrochemical gradient is created. The protons pass through the enzyme ATP synthase, which results in the production of ATP.

  4. The protons combine with the co-enzyme NADP to become reduced NADP. As the protons move from a high to low concentration gradient this is known as chemiosmosis.

  
• Why is the LIR temperature sensitive?

  It involves the enzyme Rubisco
• What is the role of ATP in the Calvin cycle?

  • To provide the energy to reduce GP to TP
  • To provide the energy to regenerate RuBP from TP
• What is the role of NADPH in the Calvin Cycle?

  To provide a H to reduce GP to TP
• What is the triose phosphate used for?

  1. To donate 1 carbon each turn of the cycle to go towards making a hexose sugar
  2. To regenerate RuBP so the cycle can continue
• Which molecules from the LDR are used in the LIR?

  1. ATP
  2. Reduced NADP
• Where does the LIR occur?

  The stroma of the chloroplast
• What can the hexose sugars made be used for?

  • Whilst glucose is the product, this monosaccharide can join to form disaccharides such as sucrose, and polysaccharides such as cellulose and starch.
  • It can also be converted into glycerol and therefore combine with fatty acids to make lipids for the plant
• What cycle is this?

  The Calvin cycle

  
• What does this graph show about limiting factors?

  Light energy is needed for LDRs so as you increase light energy the rate increases, but the rate plateaus as another factor starts limiting the rate.

  
• What does this graph show about limiting factors?

  Carbon dioxide is used to combine with RuBP in the Calvin cycle, so adding more increases the rate, but the rate plateaus as another factor starts limiting the rate.

  
• What does this graph show about limiting factors?

  Photosynthesis is enzyme-controlled. As you increase the temperature there will be more ES complexes. Too high a temperature causes enzymes to denature