8.3 Photosynthesis

Question 1

What is photosynthesis?

Answer 1

The process by which cells synthesise organic molecules from inorganic molecules in the presence of sunlight

Question 2

What does photosynthesis require?

Answer 2

A photosynthetic pigment

Question 3

Where does photosynthesis occur in plants?

Answer 3

In the chloroplast

Question 4

What are the two steps of photosynthesis?

Answer 4

Light dependent reactions
Light independent reactions

Question 5

What does the light dependent reaction do?

Answer 5

Convert light energy from the sun into ATP

Question 6

What does the light independent reaction do?

Answer 6

Use the chemical energy to synthesise organic compounds

Question 7

Where does the light dependent reaction occur?

Answer 7

In the thylakoid

Question 8

What are the three steps of the light dependent reaction?

Answer 8

Excitation of photosynthesis by light energy
Production of ATP via an electron transport chain
Reduction of NADP and the photolysis of water

Question 9

What are photosystems?

Answer 9

Groups of photosynthetic pigments embedded within the thylakoid membrane

Question 10

How are photosystems classed?

Answer 10

In accordance to their maximal absorption wavelengths

Question 11

What happens when a photosystem absorbs light energy?

Answer 11

Delocalised electrons within the pigments become energised/excited

Question 12

Where are excited electrons transferred to?

Answer 12

Carrier molecules within the thylakoid membrane

Question 13

Where are excited electrons from photosystem II transferred to?

Answer 13

An electron transport chain within the thylakoid membrane

Question 14

What do electrons lose as they are passed through the chain?

Answer 14

Energy

Question 15

What is the energy that is lost during the electron transport chain used to do?

Answer 15

To translocate H+ ions into the thylakoid

Question 16

What is caused by the build up of protons within the thylakoid?

Answer 16

An electrochemical gradient

Question 17

Where do the H+ ions return to?

Answer 17

The stroma

Question 18

How do the H+ ions return to the stroma?

Answer 18

Via the transmembrane enzyme ATP synthase/ chemiosmosis

Question 19

What does ATP synthase use to catalyse the synthesis of ATP?

Answer 19

The passage of H+ ions

Question 20

Where do the newly de-energised electrons from photosystem II go?

Answer 20

Photosystem I

Question 21

What comes first photosystem I or II?

Answer 21

Photosystem II

Question 22

What are excited electrons from photosystem I used to do?

Answer 22

Reduce NADP+

Question 23

Where may excited electrons from photosystem I be transferred to?

Answer 23

A carrier molecule

Question 24

What is needed in conjunction with ATP for the light independent reactions?

Answer 24

NADPH

Question 25

What are the electrons lost from Photosystem I replaced by?

Answer 25

De-energised electrons from photosystem II

Question 26

What replaces electrons lost from Photosystem II?

Answer 26

Electrons released from water via photolysis

Question 27

How is water split?

Answer 27

By light energy

Question 28

What is water split into?

Answer 28

H+ ions and oxygen

Question 29

What triggers the release of high energy electrons?

Answer 29

Chlorophyll in photosystems I and II absorb light

Question 30

What happens to the products of the light dependent reactions?

Answer 30

They are used in the light independent reactions

Question 31

What are the products of the light dependent reactions?

Answer 31

ATP and NADPH

Question 32

What is the production of ATP by the light dependent reactions called?

Answer 32

Photophosphorylation

Question 33

What are the two types of photophosphorylation?

Answer 33

Cyclic or non-cyclic

Question 34

What does cyclic photophosphorylation involve?

Answer 34

Only one photosystem

Question 35

What does cyclic photophosphorylation not involve?

Answer 35

The reduction of NADP+

Question 36

What happens to the de-energised electrons in cyclic photophosphorylation?

Answer 36

They return to the photosystem restoring its electron supply

Question 37

In cyclic photophosphorylation, what is not needed to happen as the electron returns to the photosystem?

Answer 37

NADP+ is not reduced and water is not needed to replenish the electron supply

Question 38

What does non-cyclic photophosphorylation involve?

Answer 38

Two photosystems and the reduction of NADP+

Question 39

What does only non-cyclic photophosphorylation allow for?

Answer 39

The synthesis of organic molecules and long term energy storage

Question 40

What can cyclic photophosphorylation be used to produce?

Answer 40

additional ATP in order to meet cell energy demands

Question 41

Where does the light independent reactions occur?

Answer 41

In the stroma

Question 42

What are the light independent reactions collectively known as?

Answer 42

The calvin cycle

Question 43

What are the three main steps of light independent reactions?

Answer 43

Carbon fixation Reduction of GP Regeneration of RUBP

Question 44

What does the calvin cycle begin with?

Answer 44

A 5C compound called ribulose biphosphate/RuBP

Question 45

What does the enzyme Rubisco do in carbon fixation?

Answer 45

Catalyses the attachment of a CO2 molecule to RuBP

Question 46

What is the result of the attachment of CO2 to RuBP?

Answer 46

An unstable 6C compound

Question 47

What happens to the 6C compound?

Answer 47

It breaks down into two 3C compounds called glycerate-3-phosphate/GP

Question 48

What does a single cycle of carbon fixation involve?

Answer 48

Three molecules of RuBP combining with three molecules of Co2 to make sic molecules of GP

Question 49

What is GP converted into?

Answer 49

Triose phosphate/TP

Question 50

How is GP converted into TP?

Answer 50

Using NADPH and ATP

Question 51

What does the reduction by NADPH transfer in step 2 of the calvin cycle?

Answer 51

Hydrogen atoms to the compound

Question 52

In step 2 of the calvin cycle, what does the hydrolysis of ATP provide?

Answer 52

Energy

Question 53

What does each GP require?

Answer 53

One NADPH and one ATP to form a triose phosphate

Question 54

What does a single cycle require in step ?

Answer 54

Six of each molecule

Question 55

Of the six molecules of TP produced per cycle, what may one TP molecule be used to form?

Answer 55

Half a sugar molecule

Question 56

What is needed to produce a single glucose monomer in the calvin cycle?

Answer 56

Two cycles

Question 57

What happens to the remaining five TP molecules?

Answer 57

They are recombined to regenerate stocks of RuBP

Question 58

What does the regeneration of RuBP require?

Answer 58

Energy derived from the hydrolysis of ATP

Question 59

What are the six steps of the calvin lollipop experiment?

Answer 59

1. Radioactive carbon-14 is added to a lollipop apparatus containing green algae 2. Light is shone on the apparatus to induce photosynthesis 3. The algae is killed by running into a solution of heated alcohol 4. Dead algal samples are analysed using 2D chromatography 5. Any radioactive carbon compounds were analysed using autoradiography 6. By comparing different periods of light exposure the order of which carbon compounds are generated was determined

Question 60

What can TP be used to do?

Answer 60

Form organic molecules or can be recombined by ATP to reform stocks of RuBP

Question 61

What are chloroplasts?

Answer 61

The solar energy plants of a cell

Question 62

What do chloroplasts do?

Answer 62

Convert light energy into chemical energy

Question 63

What are the two types of chemical energy?

Answer 63

ATP or organic compounds

Question 64

What possesses chloroplasts?

Answer 64

Only photosynthetic tissue

Question 65

What are the three evidences to suggest chloroplasts were once independent prokaryotes?

Answer 65

- they have a double membrane structure - they have their own DNA and ribosomes - their metabolic processes are susceptible to certain antibiotics

Question 66

What are the five structures of a chloroplast?

Answer 66

Thylakoids Grana Photosystems Stroma Lamellae

Question 67

What are thylakoids?

Answer 67

Flattened disks which have a small internal volume to maximise hydrogen gradient upon proton accumulation

Question 68

What are grana?

Answer 68

Thylakoids are arranged into stacks to increase SA:Vol ratio of the thylakoid membrane

Question 69

What are photosystems (structure)?

Answer 69

Pigments organised into photosystems in thylakoid membrane to maximise light absorption

Question 70

What is stroma?

Answer 70

Central cavity that contains appropriate enzymes and a suitable pH for the calvin cycle to occur

Question 71

What is lamellae?

Answer 71

Connects and separates thylakoid stacks, maximising photosynthetic efficiency