5.1 Photosynthesis

Question 1

What are the stages of photosynthesis ?

Answer 1

1. Light dependent reaction
   ○ Thylakoid membrane of chloroplast
2. Light independent reaction
   ○ Stroma of chloroplast

Question 2

What are the structures of a chloroplast ?

Answer 2

• double membrane
• stroma, containing : thylakoid membrane, small ribosomes,circular dna
• lamella
• grana

Question 3

Describe photoionisation in the light-dependent reaction (LDR)

Answer 3

1. chlorophyll absorbs light energy which excites its electron ( higher energy level )
2. So electrons are released from chlorophyll ( chlorophyll becomes positively charged )

Question 4

Describe what happens after photoionisation in the LDR

Answer 4

1. Electrons move along electron transfer chain , releasing energy
2. This energy used to actively pump protons from stroma into thylakoid
3. Protons move by FD down electrochemical gradient into stroma via atp sythase
4. Energy used to join ADP and Pi to form ATP
5. NADP accepts a proton and an electron to become reduced NADP

Question 5

Describe photolysis of water in the LDR

Answer 5

• water splits to produce protons, electrons and oxygen
  - electrons replace
  those lost from
  chlorophyll

Question 6

Describe the light independent reaction of photoythesis ( Calvin Cycle)

Answer 6

1. CO2 reacts with ribulose bisphosphate (RuBP)
2. Forming 2 glycerate 3-phosphate (GP) molecules

3.GP reduced to triose phosphate (TP)
- using products from LDR - reduced NADP and energy from ATP

4. Some TP converted to useful organic substances eg gluc
5. Some TP used to regenerate RuBP in the Calvin cycle ( using energy from ATP)

Question 7

Describe and Explain how temp affects rate of photosythesis

Answer 7

1. As temp increases, rate increases
   
   • enzymes eg rubisco gain kinetic energy
   • so more enzyme- sub complexes form
2. Above an optimum temp, rate decreases
   
   • enzymes denature as H bonds in tertiary structure break
   • so fewer enzyme-sub complexes form

Question 8

Describe and explain how light intensity affects rate of photosynthesis

Answer 8

1. As light intensity increases, rate increases
   
   • LDR increases so more ATP and reduced NADP produced
   • so light independent reaction increases as more GP reduced to TP and more TP regenerates RuBP
2. Above a certain light intensity, rate stops increases
   
   • another factor limiting eg temp

Question 9

Describe and explain how CO2 conc affects rate of photosythesis

Answer 9

1. As co2 conc increases, rate increases
   
   • light indeendent reaction increases
   • as more co2 combines with RuBP to form GP
   • so more GP reduced to TP
   • so more TP converted to organic substances and more RuBP regenerated
2. Above a certain co2 conc , rate stops increasing
   
   • another factor is limiting eg temp

Question 10

Explain the key consideration when evaluating data relating to agricultural practices used to overcome the effect of limiting factors

Answer 10

1. Agricultural practices should increase the rate of photosynthesis leading to increased yield
   
   • as more glucose produced for faster resp
   • so more ATP to release energy for growth eg cell division

2.But profit from extra yield should be greater than costs ( money and environmental costs