Photosynthesis

Question 1

What is the equation for photosynthesis?

Answer 1

6CO2 + 6H2O + light energy → C6H12O6 + 6O2

Question 2

What are the main functions of chloroplasts?

Answer 2

• To absorb light energy to drive photosynthesis.
• To convert light energy into chemical energy.

Question 3

What are thylakoids?

Answer 3

Flattened sacs that contain pigments in their membranes to absorb light for the light dependent reaction.

Question 4

What are grana?

Answer 4

Stacks of thylakoids

Question 5

What are lamellae?

Answer 5

Membranous extensions that connect thylakoids

Question 6

What is the stroma?

Answer 6

A fluid surrounding the thylakoids where the light independent reaction occurs.

Question 7

What are chloroplast DNA used for?

Answer 7

Contain the genes that code for proteins involved in photosynthesis.

Question 8

What is Chlorophyll a?

Answer 8

The main pigment that absorbs red and blue light and reflects green.

Question 9

What is chlorophyll b?

Answer 9

An accessory pigment mostly found with chlorophyll a in light-harvesting complexes.

Question 10

What are xanthophylls and carotenoids?

Answer 10

Absorb different wavelengths than chlorophyll, broadening the spectrum of light that can drive photosynthesis.

Question 11

What are clusters of pigments called and where are they found?

Answer 11

Photosystems.
Found in the thylakoid membranes.

Question 12

What does each photosystem have?

Answer 12

A light harvesting system that absorbs light energy which is then transferred to a reaction centre. This emits high energy electrons to drive light dependent reactions.

Question 13

What is photophosphorylation?

Answer 13

Where ATP is formed using light energy.

Question 14

What is non-cyclic photophosphorylation?

Answer 14

The use of water and light energy to produce ATP, reduced NADP and oxygen.

Question 15

Describe the first stage in non-cyclic photophosphorylation?

Answer 15

• Light energy is absorbed by pigments.
• This excited electrons in the pigments in photosystem 1 and photosystem 2 reaction centres.
• Electrons are lost from the pigments.

Question 16

Describe the second stage in non-cyclic photophosphorylation?

Answer 16

• Electrons are transferred to an electron carrier molecule.
• They are passed along the chain, releasing energy as they go.
• The electron from PSII replaces the lost electron from PSI.

Question 17

Describe the third stage of non-cyclic photophosphorylation?

Answer 17

• The photolysis of water where light is used to split water into electrons, protons and oxygen.
• 2H2O → 4H+ + 4e- + O2.
• The electrons replace those lost from PSII.
• The protons are used for ATP production and combine with electrons to reduce NADP.

Question 18

Describe chemiosmosis

Answer 18

• The energy lost by electrons along the electron transport chain pumps protons across the thylakoid membrane.
• This produces a proton gradient.
• The protons diffuse through ATP synthase to produce ATP from ADP and an inorganic phosphate.

Question 19

How is NADP reduced?

Answer 19

• NADP takes up protons and electrons from PSI in the stroma and is reduced.
• Reduced NADP is carried into the light independent reaction.

Question 20

When is cyclic photphosphorylation used?

Answer 20

When NADP is not available.

Question 21

Describe cyclic photophosphorylation

Answer 21

• Light energy is absorbed by pigments and excites electrons in the pigments in the PSI only.
• Electrons are lost
• They are transferred to an electron carrier molecule and passed along an electron carrier chain, releasing energy.
• This powers proton transport across the thylakoid membrane.
• ATP is produced as protons flow back into the stroma through ATP synthase.
• Electrons are returned to the PSI so no NADP is reduced.