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IB Biology > 8.3 Photosynthesis > Flashcards

8.3 Photosynthesis Flashcards

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1
Q

What is photosynthesis?

A

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

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2
Q

What does photosynthesis require?

A

A photosynthetic pigment

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3
Q

Where does photosynthesis occur in plants?

A

In the chloroplast

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4
Q

What are the two steps of photosynthesis?

A

Light dependent reactions
Light independent reactions

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5
Q

What does the light dependent reaction do?

A

Convert light energy from the sun into ATP

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6
Q

What does the light independent reaction do?

A

Use the chemical energy to synthesise organic compounds

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7
Q

Where does the light dependent reaction occur?

A

In the thylakoid

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8
Q

What are the three steps of the light dependent reaction?

A

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

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9
Q

What are photosystems?

A

Groups of photosynthetic pigments embedded within the thylakoid membrane

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10
Q

How are photosystems classed?

A

In accordance to their maximal absorption wavelengths

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11
Q

What happens when a photosystem absorbs light energy?

A

Delocalised electrons within the pigments become energised/excited

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12
Q

Where are excited electrons transferred to?

A

Carrier molecules within the thylakoid membrane

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13
Q

Where are excited electrons from photosystem II transferred to?

A

An electron transport chain within the thylakoid membrane

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14
Q

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

A

Energy

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15
Q

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

A

To translocate H+ ions into the thylakoid

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16
Q

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

A

An electrochemical gradient

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17
Q

Where do the H+ ions return to?

A

The stroma

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18
Q

How do the H+ ions return to the stroma?

A

Via the transmembrane enzyme ATP synthase/ chemiosmosis

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19
Q

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

A

The passage of H+ ions

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20
Q

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

A

Photosystem I

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21
Q

What comes first photosystem I or II?

A

Photosystem II

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22
Q

What are excited electrons from photosystem I used to do?

A

Reduce NADP+

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23
Q

Where may excited electrons from photosystem I be transferred to?

A

A carrier molecule

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24
Q

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

A

NADPH

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25
Q

What are the electrons lost from Photosystem I replaced by?

A

De-energised electrons from photosystem II

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26
Q

What replaces electrons lost from Photosystem II?

A

Electrons released from water via photolysis

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27
Q

How is water split?

A

By light energy

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28
Q

What is water split into?

A

H+ ions and oxygen

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29
Q

What triggers the release of high energy electrons?

A

Chlorophyll in photosystems I and II absorb light

30
Q

What happens to the products of the light dependent reactions?

A

They are used in the light independent reactions

31
Q

What are the products of the light dependent reactions?

A

ATP and NADPH

32
Q

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

A

Photophosphorylation

33
Q

What are the two types of photophosphorylation?

A

Cyclic or non-cyclic

34
Q

What does cyclic photophosphorylation involve?

A

Only one photosystem

35
Q

What does cyclic photophosphorylation not involve?

A

The reduction of NADP+

36
Q

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

A

They return to the photosystem restoring its electron supply

37
Q

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

A

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

38
Q

What does non-cyclic photophosphorylation involve?

A

Two photosystems and the reduction of NADP+

39
Q

What does only non-cyclic photophosphorylation allow for?

A

The synthesis of organic molecules and long term energy storage

40
Q

What can cyclic photophosphorylation be used to produce?

A

additional ATP in order to meet cell energy demands

41
Q

Where does the light independent reactions occur?

A

In the stroma

42
Q

What are the light independent reactions collectively known as?

A

The calvin cycle

43
Q

What are the three main steps of light independent reactions?

A

Carbon fixation
Reduction of GP
Regeneration of RUBP

44
Q

What does the calvin cycle begin with?

A

A 5C compound called ribulose biphosphate/RuBP

45
Q

What does the enzyme Rubisco do in carbon fixation?

A

Catalyses the attachment of a CO2 molecule to RuBP

46
Q

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

A

An unstable 6C compound

47
Q

What happens to the 6C compound?

A

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

48
Q

What does a single cycle of carbon fixation involve?

A

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

49
Q

What is GP converted into?

A

Triose phosphate/TP

50
Q

How is GP converted into TP?

A

Using NADPH and ATP

51
Q

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

A

Hydrogen atoms to the compound

52
Q

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

A

Energy

53
Q

What does each GP require?

A

One NADPH and one ATP to form a triose phosphate

54
Q

What does a single cycle require in step ?

A

Six of each molecule

55
Q

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

A

Half a sugar molecule

56
Q

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

A

Two cycles

57
Q

What happens to the remaining five TP molecules?

A

They are recombined to regenerate stocks of RuBP

58
Q

What does the regeneration of RuBP require?

A

Energy derived from the hydrolysis of ATP

59
Q

What are the six steps of the calvin lollipop experiment?

A
  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
60
Q

What can TP be used to do?

A

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

61
Q

What are chloroplasts?

A

The solar energy plants of a cell

62
Q

What do chloroplasts do?

A

Convert light energy into chemical energy

63
Q

What are the two types of chemical energy?

A

ATP or organic compounds

64
Q

What possesses chloroplasts?

A

Only photosynthetic tissue

65
Q

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

A
  • they have a double membrane structure
  • they have their own DNA and ribosomes
  • their metabolic processes are susceptible to certain antibiotics
66
Q

What are the five structures of a chloroplast?

A

Thylakoids
Grana
Photosystems
Stroma
Lamellae

67
Q

What are thylakoids?

A

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

68
Q

What are grana?

A

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

69
Q

What are photosystems (structure)?

A

Pigments organised into photosystems in thylakoid membrane to maximise light absorption

70
Q

What is stroma?

A

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

71
Q

What is lamellae?

A

Connects and separates thylakoid stacks, maximising photosynthetic efficiency

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