5A Photosynthesis

Question 1

Where in the chloroplast does the light dependent reaction occur?

Answer 1

thylakoid membrane

Question 2

What is the simple description of what happens during the light dependent reaction?

Answer 2

• makes ATP
• photolysis of water

Question 3

Compare and contrast oxidation and reduction in 3 ways

Answer 3

oxidation
- loses e-
- loses H
- gains O

reduction
- gains e-
- gains H
- loses O

Question 4

What happens when light is absorbed by psII up until the electron energy is lost?

Answer 4

• psII becomes photoionised, increasing the energy potential of an electron
• electron released and travels along ETC via redox reactions
• electron energy decreases during transport

Question 5

What happens to the energy lost from the electron that is released by psII?

CHEMIOSMOSIS

Answer 5

• energy is transferred to proton pumps which move H+ ions from the stroma to the thylakoid lumen
• this creates an electrochemical gradient of H+ ions
• H+ ions return to stroma down proton gradient via ATP synthase enzyme

Question 6

What kind of enzyme is involved in chemiosmosis for transport of H+ ions?

Answer 6

transmembrane ion ATP synthase

Question 7

What is the movement of H+ ions in chemiosmosis used for?

Answer 7

• used to catalyse ATP synthesis
• this is called photophosphorylation

Question 8

Where do the electrons from psII that have lost energy go after their transport along ETC?

Answer 8

• the newly de-energised electron is taken up by psI
• excited electron from psI may be transferred to an electron carrier and used to reduce NADP+
• this produces NADPH

Question 9

What is NADPH needed for?

Answer 9

the light independent reaction

Question 10

What are the electrons lost from psI replaced by?

Answer 10

de-energised electrons from psII

Question 11

What are the electrons lost from psII replaced by?

Answer 11

electrons released from water via photolysis

Question 12

Describe photolysis

Answer 12

• water-splitting
• water is split by light energy into H+ ions, oxygen and electrons

Question 13

What are the products of photolysis used for in photosynthesis?

Answer 13

• H+ ions = used in chemiosmosis
• oxygen = released as a by product
• electrons = used to reduce NADP+ and synthesise ATP

Question 14

Describe the simple outcome of the light independent reaction

Answer 14

• uses ATP and NADP to reduce glycerate 3-phosphate

Question 15

Where does the light independent reaction occur?

Answer 15

the stroma of chloroplasts

Question 16

Describe the first step of the calvin cycle

Answer 16

• co2 diffuses from the atmosphere into the leaf through the stomata and dissolves in water around the walls of the mesophyll cells
• it then diffuses through the cell surface membrane, cytoplasm and chloroplast membranes into the stroma of the chloroplast

Question 17

What happens in the calvin cycle when co2 has diffused into the stroma?

Answer 17

• in the stroma the co2 reacts with the 5 carbon compound RIBULOSE BISPHOSPHATE (RuBP)
• this reaction is catalysed by an enzyme called ribulose bisphosphate carboxylase (aka rubisco)

Question 18

What happens in the calvin cycle when co2 has reacted with RuBP?

Answer 18

• 2 molecules of GP are produced

Question 19

What is GP?

Answer 19

GP is a 3 carbon compound called glycerate 3-phosphate

Question 20

What enzyme catalyses the reaction between co2 and RuBP?

Answer 20

rubisco / ribulose bisphosphate carboxylase

Question 21

What happens in the calvin cycle when 2 molecules of GP are produced?

Answer 21

• reduced NADP from the light dependent reaction is used to reduce GP to TP using energy from ATP

Question 22

What is TP?

Answer 22

triose phosphate

Question 23

What happens in the calvin cycle when GP has been reduced to TP?

Answer 23

• the NADP is reformed and goes back to the light dependent reaction to be reduced again

Question 24

What happens to the TP that is produced in the calvin cycle?

Answer 24

• some TP molecules are converted into organic substances that plants require
• most TP molecules are used to regenerate RuBP using ATP from the light independent reaction

Question 25

What kinds of substances could TP be converted into that plants require?

Answer 25

organic substances such as starch, cellulose, lipids, glucose, amino acids and nucleotides