Photosynthesis

Question 1

What is the general equation for photosynthesis (GCSE)?

Answer 1

6CO2 + 6H2O -> C6H12O6 + 6O2

Question 2

What does the non-cyclic light dependent reaction produce?

Answer 2

Oxygen, ATP and NADPH

Question 3

How is water broken up before the light dependent reaction?

Answer 3

Through Photolysis

Question 4

Describe the (non cyclic) light dependent reaction.

Answer 4

1) Photolysis produces protons, electrons and oxygen
2) Light energy is absorbed by PSII and causes electrons to move to a high energy level.
3) These high energy electrons move down the electron transport chain, losing energy which is used to pump protons into the thylakoid.
4) Electrons from photolysed water replaces electrons in PSII
5) Protons move down their conc gradient through ATP synthase, forming ATP.
6) Light energy is absorbed by PSI, exciting the electrons, which are then transferred to NADP (along with protons) to form NADPH

Question 5

What do chloroplasts contain?

Answer 5

Photosynthetic pigments (eg chlorophyll a&b)

Question 6

What are photosynthetic pigments?

Answer 6

Coloured pigments that absorb the light energy needed for photosynthesis

Question 7

Describe photoionisation

Answer 7

Light energy is absorbed by chlorophyll, which excites the electrons, giving them more energy until they can be released from the chlorophyll molecule.

Question 8

What is the equation for the photolysis of water?

Answer 8

2H2O -> O2 + 4H+ + 4e-

Question 9

What is chemiosmotic theory?

Answer 9

The process of electrons flowing down the electron transport chain, creating a proton gradient across the membrane to drive ATP synthesis.

Question 10

Describe the cyclic light dependent reaction.

Answer 10

1) Light is absorbed by photosystem 1, photoionising this until electrons are emitted
2) These electrons move down the electron transport chain, losing energy and pumping protons into the thylakoid membrane
3) These protons form ATP through chemiosmosis
4) The electrons rejoin the photosystem 1

Question 11

What does cyclic photophosphorylation produce?

Answer 11

Only ATP

Question 12

Where in the chloroplast does the light-dependent reactions occur?

Answer 12

In the thylakoid membranes

Question 13

What is the light independent reaction also known as?

Answer 13

The Calvin cycle

Question 14

Where does the light independent reaction take place?

Answer 14

In the stroma

Question 15

Draw the calvin cycle.

Answer 15

Question 16

What is the next step in the calvin cycle after the formation of ribulose bisphosphate

Answer 16

CO2 enters the leaf through the stomata and diffuses into the stroma. The enzyme rubisco catalyses the formation of 2 glycerate 3-phosphate (GP) from ribulose bisphosphate and CO2

Question 17

What is the next step in the calvin cycle after the formation of 2x Glycerate 3-phosphates.

Answer 17

2x triose phosphates are formed, requiring ATP and NADPH. Some triose phosphate is then converted into useful compounds (eg glucose) and some contines to regenerate RuBP

Question 18

How many molecules of Triose phosphate are used to regenerate Ribulose Bisphosphate?

Answer 18

5 out of 6

Question 19

How many turns of the calvin cycle is required to form 1 hexose sugar?

Answer 19

6 turns.

Question 20

How much ATP and NADPH does 6 turns of the calvin cycle require?

Answer 20

18 ATP and 12 NADPH

Question 21

What can triose phosphate and glycerate 3-phosphate form?

Answer 21

• Carbohydrates
• Lipids
• Amino acids

Question 22

What does chlorophyll contain?

Answer 22

Magnesium, which releases electrons when it is exposed to light