Photosynthesis

Where does the light-dependent reaction take place?

Where does the light-dependent reaction take place?

on thylakoid membrane in chloroplast

What is the first stage of the light-dependent reaction?

chlorophyll absorbs light energy → excites electrons to a higher energy level → released from chlorophyll = photoionisation

What is the second stage of the light-dependent reaction?

Production of ATP

• electrons pass down ETC via redox reactions, losing energy at each step

• energy; protons→stroma to thylakoid (a.t)

• electrochemical gradient created across thylakoid membrane (higher in t)

• protons down EC gradient (f.d) via ATP synthase in thylakoid membrane

• ADP + Pi → ATP (photophosphorylation) - chemiosmotic theory

What is the third stage of the light-dependent reaction?

Production of reduced NADP

• electrons excited + transferred to NADP to reduce NADP

What is the fourth stage of the light-dependent reaction?

Photolysis

• splitting of water using light energy

• produces protons, electrons + oxygen

What are the products of the LDR?

• ATP for the LIDR

• NADPH for the LIDR

• oxygen for respiration

What is the light-independent reaction (Calvin Cycle)?

1. CO2 reacts with ribulose biphosphate (RuBP) catalysed by enzyme rubisco

2. produce 2x glycerine-3-phosphate (GP)

3. GP reduced to triose phosphate (TP)

   • using energy from hydrolysis of ATP and H+ from reduced NADP

4. some TP → useful organic substances, e.g glucose

5. TP used to regenerate RuBP (using ATP)

Why is temperature a limiting factor?

increases → increases rate

• limits LIDR as rubisco is controlled

• more KE → more ES complexes

• H bonds break → a.s changes shape → enzyme denatures → fewer E-S complexes

Why is light intensity a limiting factor?

increases → increases rate

• if reduced; ATP and NADPH reduced

• LDR limited, less photoionisation of chlorophyll

• LIDR slows, GP not reduced to TP, no TP to regenerate RuBP

Why is CO2 conc. a limiting factor?

increases → increases in rate

• if reduced; limited LIDR reaction

• less CO2 to combine with RuBP to form GP

• less GP reduced to TP

• less TP converted to organic substances + to regenerate RuBP

What agricultural practices overcome limiting factors?

1. artificial lighting

2. heating greenhouse

3. burning fuel

= photosynthesis increases

→ faster production of glucose → more respiration

→ more ATP - growth, e.g. cell division, protein-synthesis

→ higher yield = more profit