5.6 PHOTOSYNTHESIS

Question 1

Structure of the chloroplast

Answer 1

Question 2

What are thylakoids in the chloroplast?

Answer 2

• Folded membranes which contain photosynthetic pigment (chlorophyll) and photosystems

Question 3

What is stroma in the chloroplast?

Answer 3

• fluid centre of the chloroplast with RUBISCO enzymes

Question 4

What is the grana in the chloroplast?

Answer 4

• stacks of thylakoids

Question 5

What is the outer membrane of a chloroplast?

Answer 5

• Highly permeable membrane that controls the entry/exit in chloroplast

Question 6

What is a photosystem and where are they located?

Answer 6

• Photosystems are a bunch of photosynthetic pigments found in the thylakoids

Question 7

What is meant by a photosynthetic pigment?

Answer 7

• Different pigments that absorb specific wavelengths of light

Question 8

What are *accessory pigments**, where are they based in photosystems and what do they do?

Answer 8

• Chlorophyll B/ Carotenoids
• Light harvesting system
• Light energy absorbed is passed to the reaction centres

Question 9

Where is the *primary pigment**, where is it based in photosystems and what does it do?

Answer 9

• Chlorophyll A
• Reaction centres
• Where light dependant stage happens

Question 10

State the Rf value equation

Answer 10

Question 11

Where does the light-dependant stage occur?

Answer 11

• Thylakoids

Question 12

What reactions does the light-dependant stage consist of? (4)

Answer 12

1) Non-cyclic photophosphporilation
2) Cyclic photophosphporilation
3) Photolysis
4) Chemiosmosis

Question 13

What two things are produced by the light-dependant stage?

Answer 13

• ATP
• Reduced NADP/NADPH

Question 14

Name the two photosystems used in the light-dependant stage.

Answer 14

• PSII (used first) and PSI (used after)

Question 15

Describe non-cyclic photophosphporilation

Answer 15

• Light energy absorbed by photosynthetic pigments causes electrons in the reaction centre chlorophyll of PSII to become excited & released to electron carriers
• Electron carriers combine with electron (to become reduced to Fe2+ then donates the electron to next electron carrier to become re-oxidised to Fe3+) which moves excited electrons along the electron transport system to PSI
• The movement of electrons through the electron transport chain results in ATP production at the end via chemiosmosis
• Electrons lost from the reaction centre chlorophyll of PSII are replaced by electrons from photolysis and electrons lost from reaction centre chlorophyll of PSI are replaced by electrons from PSII
• At PSI reaction centre the electrons are released and accepted by the coenzyme NADP along with H+ protons from photolysis to produce reduced NAPD (NADPH)

Question 16

Describe cyclic photophosphporilation

Answer 16

• Some electrons released from the reaction centres of PSI are not picked up by the coenzyme NADP and are instead recyled back into PSI
• The movement of electrons along the electron transport chain still results in ATP production by chemiosmosis
• However reduced NADP (NADPH) is not produced

Question 17

Describe photolysis

Answer 17

• Light energy absorbed by chlorophyll in PSII is used (along with an enzyme) to split water into oxygen, H+ and e-
• The H+ proton is picked up by NADP to produce reduced NADP (NADPH)
• The electron from this replaces the electrons lost from the reaction centre chlorophyll of PSII
• The oxygen is used for respiration or diffuses out the leaf

Question 18

Describe chemiosmosis

Answer 18

• When excited electrons move along the electron transport chain through the embedded electron carriers in thylakoid membrane energy is released
• Some of this energy is used to pump H+ protons from photolysis across the thylakoid membrane from the stroma to the thylakoid space
• This creates an electrochemical gradient as many H+ protons are now in the thylakoid space
• As a result, H+ protons diffuse down the electrochemical gradient, back across the thylakoid membrane through the enzyme ATP synthase
• When H+ protons pass through, ATP synthase converts ADP + Pi into ATP
• The H+ protons now combine with the coenzyme NADP to form reduced NAPD (NAPH)

Question 19

Describe the three roles of water in photosynthesis

Answer 19

1) Source of H+ protons for photophosphorilation (NADPH production)
2) Replaces electrons lost from reaction centre chlorophyll of PSII
3) Keeps plant turgid

Question 20

Where does the light-independant stage occur?

Answer 20

• Stroma

Question 21

What does the light-independant stage consist of?

Answer 21

• The calvin cycle

Question 22

Draw and describe the calvin cycle

Answer 22

Question 23

What is produced in the light-independant stage?

Answer 23

• Hexose sugar

Question 24

State the uses of TP during the calvin cycle

Answer 24

• Can form the disaccarise sucrose
• Can form the polysaccarides starch or cellulose
• Can form amino acids
• Can form lipids
• Can regenerate RuBP for calvin cycle

Question 25

The three limiting factors of photosynthesis?

Answer 25

Question 26

How does decreasing light intensity affect levels of GP, TP and RuBP?

Answer 26

• Lower light intensity reduces GP, TP and RuBP because ATP and NADPH is reduced during the light dependent stage

Question 27

How does **decreasing carbon dioxide* affect levels of GP, TP and RuBP?

Answer 27

• Lower carbon dioxide increases RuBP but reduces GP, TP because RuBP accumulates as it cannot react with low levels of carbon dioxide meaning GP and TP cannot be produced.

Question 28

How does **increasing temperature* affect levels of GP, TP and RuBP?

Answer 28

• Higher temperature increases GP, TP and RuBP as more kinetic energy means more successful collisions until temperature is too high, RuBP denatures