Photosynthesis

Question 1

Define thylakoids

Answer 1

Fluid filled sacs stacked up in the chloroplast forming grana linked together by lamellae

Question 2

Define stroma

Answer 2

Gel like substance that contains enzymes, sugars and organic acids

Question 3

Where does light dependent reactions happen?

Answer 3

Thylakoid membranes

Question 4

Where does light dependent reactions happen?

Answer 4

Stroma

Question 5

How is ATP produced in the light dependent reaction?

Answer 5

• Chlorophyll in PSII absorbs light energy → excites electrons to a higher energy level → releasing them from chlorophyll (photoionisation)
  PRODUCTION OF ATP
  1) Electrons pass down the electron transfer chain from PSII to PSI via redox reactions, losing energy at each step
  2) This energy is used to actively transport protons from the stroma into the thylakoid membrane
  3) Creating an electrochemical gradient across the thylakoid membrane
  4) Protons move down the electrochemical gradient into the stroma via enzyme ATP synthase embedded in thylakoid membrane
  5) Energy from this allows ADP + Pi → ATP (photophosphorylation)
  This is called the chemiosmotic theory.

Question 6

How is reduced NADP (NADPH) produced in the light dependent reaction?

Answer 6

1) in PSI electrons are excited and transferred to NADP which excites electrons to an even higher energy level
2) Electrons are transferred to NADP along with a proton from the stroma to form reduced NADP (NADPH)

Question 7

What is photolysis?

Answer 7

the splitting of water using light energy

Question 8

What are the products of photolysis?

Answer 8

protons, electrons and oxygen

Question 9

What are the products of the light dependent reaction?

Answer 9

-ATP,
-Reduced NADP
-Oxygen

Question 10

Describe the process of the calvin cycle in light dependent reactions?

Answer 10

1) CO2 reacts with RuBP (5C) → catalysed by enzyme rubisco
2) Produces 2 molecules of GP (3C)
3) GP is reduced to TP using energy from ATP and the H+ from reduced NADP
4) Some TP is converted to useful organic substances (e.g. hexose sugars)
5) 5/6 TP is used to regenerate RuBP using the rest of ATP

Question 11

How does temperature affect photosynthesis?

Answer 11

• Rate of photosynthesis increases as temp increases up to an optimum, decreases after

-Limits light dependent reaction as it’s enzyme controlled (rubisco)

Increasing temp upto optimum means
- More E-S complexes → rubisco
Above optimum…
-H bonds in tertiary structure break → active site changes shape → fewer E-S complexes

Question 12

How does light intensity affect photosynthesis?

Answer 12

• Rate of photosynthesis increases as light intensity increases (then plateaus)
  If light intensity was dramatically reduced…
  -Levels of ATP and Reduced NADP would fall because..
  -Light dependent reaction is limited as less photoionisation of chlorophyll (and less photolysis) (less excited electrons)

-So light dependent reaction would slow/stop
- GP cannot be reduced to TP
- Less TP and GP converted to organic substances e.g hexose and regenerate RuBP

Question 13

How does CO2 concentration effect photosynthesis?

Answer 13

• Rate of photosynthesis increases as CO2 conc increases (then plateaus)

If CO2 conc is dramatically decreased…
- Limits light dependent reaction
- Less CO” to combine RuBP to form GP
-Less GP reduced to TP
- Less TP and GP to be converted to organic substances e.g. hexose sugar and to regenerate RuBP

Question 14

What happens if limiting factors are kept minimal in photosynthesis?

Answer 14

• Faster production of glucose allowing faster respiration
• More ATP to provide energy for growth e.g cell division, protein synthesis
  → Higher yield so more profit