5.2.1 - Photosynthesis

a) What is the interrelationship between respiration and photosynthesis?

• Products of photosynthesis and is the raw materials for respiration

• Important for the cycle of CO2 and O2

b) Label the diagram of chloroplasts?

What are the two main sites in the chloroplasts used for photosynthesis?

Thylakoids

• Stacks of thylakoids = grana 

• Grana this is were LDR occurs due to large SA increases light absorptions

• Contains its own DNA to create proteins to hold photosynthetic pigments in place / photosystems 

Stroma:

• Surrounds thylakoids so products from LDR can be used in LIDR

ci) What is the importance of photosynthetic pigments ad examples?

• They absorb light at different wave lengths 

• Trap light energy 

Example:

• PS1 = 700nm

• PS2 = 680nm

cii) How can you separate photosynthetic pigments and how do you work out Rf value?

Thin Layer Chromatography

Distance of spot/ Distance of solvent

d) What is the non- cyclic Light Dependent Stage of Photosynthesis?

1. Light hits PS2 - causing electrons to get excited

2. This causes them to pass across ETC with electron carriers and forms ATP

3. Electrons in PS1 is then lost due to the light striking

4. H+ ions from photolysis of water passes with electron which then binds to NADP to form reduced NADP = NADPH

5. Electrons oxidised from PS2 replaces electrons lost from PS1

6. Protons take part in chemosis and forms ATP then the NADP is in the stroma for LIDR

What is the cyclic process for Light Dependent Stage of Photosynthesis?

• Only occurs in PS1 of 700nm

1. Light hits PS1 - causes electron to get excited and gain energy

2. They leave chloroplasts to go to the ETC

3. Through the ETC it doesn’t go through photolysis which means doesn’t produce reduced NADP/ O2/ H2 is formed but forms small amount of ATP

4. Goes back to the PS1

Why does chloroplasts only have PS1?

• Only form ATP

• Allows K ions to enter cell to lower water potential

• Allows guard cells to cell and stoma to open

e) What happens in Light Independent Stage of Photosynthesis?

• Calvin Cycle

• Uses products from LDR which lead from the stroma

• CO2 used for carbon fixation

Explain the Calvin Cycle?

1. Carbon dioxide combines with ribulose bisphosphate (RuBP) in a reaction catalysed by the enzyme RuBisCO

2. Forming an unstable six-carbon compound which splits into two molecules of glycerate 3-phosphate (GP).

3. GP is then reduced to triose phosphate (TP) using ATP and reduced NADP from the light-dependent stage.

4. Some TP is used to produce glucose and other organic molecules.

5. Most TP is used to regenerate RuBP, which requires ATP.
   Regeneration of RuBP allows the Calvin cycle to continue.