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Biology > 5.2.1 - Photosynthesis > Flashcards

5.2.1 - Photosynthesis Flashcards

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1
Q

What is photosynthesis ?

A

The process by which energy, in the form of light, is used to build organic molecules, such as glucose

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2
Q

What is the equation for photosynthesis ?

A

6CO2 + 6H2O -> C6H12O6 + 6O2

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3
Q

What are autotrophic organisms ?

A

Organisms that produce their own energy via photosynthesis

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4
Q

What are heterotrophic organisms ?

A

Organisms that obtain complex organic molecules by eating other organisms

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5
Q

What do both autotrophic and heterotrophic organisms do ?

A

They break down organic molecules during the process of respiration to release the energy they need to drive metabolic processes

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6
Q

Where does photosynthesis take place ?

A

It takes place in the chloroplasts

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7
Q

What is the structure of the chloroplasts ?

A
  • Membranes form flattened sacs called thylakoids
  • Thylakoids are stacked to form grana
  • The grana are joined by lamellae
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8
Q

What is an adaptation of the granum towards photosynthesis ?

A

They provide a large surface area to maximise the absorption of light essential in the first step of photosynthesis

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9
Q

What pigment absorbs light in the chloroplasts ?

A

Chlorophyll

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10
Q

Where is chlorophyll found ?

A

In the chloroplasts

It is embedded within the thylakoid membranes

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11
Q

What is the fluid in the chloroplast called ?

A

Stroma

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12
Q

What is the stroma the site of ?

A

The site of many chemical reactions resulting in the formation of complex organic molecules

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13
Q

What gives pigments their colours ?

A
  • The wavelength of light that they absorb
  • It is specific to that pigment
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14
Q

What is the primary pigment in photosynthesis ?

A

Chlorophyll

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15
Q

What light does chlorophyll absorb ?

A
  • Red and blue light
  • Reflects green light
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16
Q

What is the primary pigment that absorbs light ?

A

Chlorophyll a

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17
Q

What are some of the other pigments that also absorb light ?

A
  • Chlorophyll b
  • Xanthophylls
  • Carotenoids
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18
Q

What do the different combinations of pigments cause ?

A

They cause leaves having different shades of colours

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19
Q

What pigments are embedded in the thylakoid membrane of the chloroplast ?

A
  • Chlorophyll b
  • Xanthophylls
  • Carotenoids
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20
Q

What do all these pigments form ?

A

A light harvesting system called an antennae complex

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21
Q

What is the role of the antennae complex ?

A

To absorb light energy of different wavelengths and transfer this energy to the reaction centre

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22
Q

What is the reaction centre ?

A

This is where the reactions that are involved in photosynthesis take place

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23
Q

What pigment is present in the reaction centre ?

A

Chlorophyll a

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24
Q

What are the antennae complex and the reaction centre collectively known as ?

A

The photosystem

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25
Q

What are the two stages of photosynthesis ?

A
  • Light dependent stage
  • Light independent stage
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26
Q

What is the light dependent stage ?

A
  • Energy from sunlight is absorbed and used to form ATP
  • Hydrogen from water is used to reduce NADP to NADPH
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27
Q

What is the light independent stage ?

A
  • Hydrogen from NADPH and CO2 is used to build organic molecules
  • ATP supplies the required energy
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28
Q

What subsections are there to the light dependent stage ?

A
  • Non-cylic photophosphorylation
  • Photolysis
  • Cyclic photophosphorylation
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29
Q

What photosystems are involved in non cyclic photophosphorylation ?

A
  • Photosystem 1
  • Photosystem 2
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30
Q

What wavelength does the reaction centre of PS1 absorb light at ?

A

700 nm

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31
Q

What wavelength does the reaction centre of PS2 absorb light at ?

A

680 nm

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32
Q

What does the absorption of light do at the reaction centres ?

A

It excites electrons at the reaction centres of the photosystems

33
Q

What happens to the excited electrons from PS2 ?

A

They are released from the reaction centre of PS2 and are passed to an electron transport chain.

34
Q

What happens after the electrons from the reaction centre of PS2 are lost ?

A

They are replaced, from the electrons given off by photolysis

35
Q

During what process in photosynthesis is ATP produced ?

A

Chemiosmosis

36
Q

How is ATP produced in PS1 (after PS2) ?

A
  • The excited electrons are released from the reaction centre and passed on to another electron transport chain.
  • By chemiosmosis
37
Q

What happens after the electrons from the reaction centre of PS1 are lost ?

A

They are replaced by electrons that have just travelled along the first electron transport chain after being released from PS2

38
Q

What happens to the electrons that leave the electron transport chain of PS1 ?

A

They are accepted, along with a hydrogen ion, by NADP, forming NADPH

39
Q

What does NADPH provide ?

A

It provides the hydrogen in the production of organic molecules in the light independent stage

40
Q

What are these two electron transport chains called ?

A

The Z scheme

41
Q

What does photolysis involve ?

A

Water molecules are split into hydrogen ions, electrons and oxygen molecules using energy from the sun

42
Q

Where do the electrons released by photolysis go ?

A

They replace the electrons lost from the reaction centre of PS2

43
Q

How does the oxygen evolving complex that forms in PS2 act ?

A

It is an enzyme that catalyses the breakdown of water

44
Q

What are water molecules split into in photolysis ?

A
  • Hydrogen ions
  • Electrons
  • Oxygen molecules
45
Q

How are the water molecules split in photolysis ?

A

Using energy from the sun

46
Q

What is oxygen gas released as in photolysis ?

A

A by product

47
Q

Where are the hydrogen ions released into in photolysis ?

A
  • Into the lumen of the thylakoids
  • They increase the proton concentration across the membrane
48
Q

What do the hydrogen ions drive the formation of ?

A

As they move back through the membrane down a concentration and electrochemical gradient, more ATP is formed

49
Q

What happens when the hydrogen ions are returned to the stroma ?

A

They combine with NADP and an electron from PS1 to form NADPH

50
Q

Where is NADPH used ?

A

Light independent reactions of photosynthesis

51
Q

What is cyclic photophosphorylation ?

A

The electrons leaving the electron chain in PS1 can return to PS1, instead of forming NADP, leading to cyclic phosphorylation

52
Q

What does cyclic photophosphorylation allow to happen ?

A

PS1 can still lead to the production of ATP without any electrons being supplied from PS2

53
Q

Is NADPH produced in cyclic photophosphorylation ?

A

No

54
Q

Where does the light independent stage take place ?

A

Takes place in the stroma of chloroplasts and uses carbon dioxide as a raw material

55
Q

What reactants are required for the light independent stage ?

A
  • ATP
  • Reduced NADP
56
Q

What is the calvin cycle ?

A

Series of reactions that takes place in the light independent stage to form organic molecules

57
Q

Where does carbon dioxide enter for the calvin cycle ?

A
  • It enters the intracellular spaces within the spongy mesophyll of leaves by diffusion from the atmosphere through stomata
  • Diffuses into the stroma of chloroplasts
58
Q

What does carbon dioxide react with when it enters the calvin cycle ?

A

It reacts with a 5 carbon molecule called Ribulose bisphosphate (RuBP)

59
Q

What happens to the carbon when it reacts with RuBP ?

A
  • The carbon becomes fixed

This comes under carbon fixation

60
Q

What is formed when CO2 and RuBP react ?

A

An unstable 6 carbon compound

61
Q

What enzyme catalyses the reaction between CO2 and RuBP ?

A

Ribulose biphosphate carboxylase (RuBisCO)

62
Q

What is RuBisCO ?

A
  • It is the key enzyme in photosynthesis
  • It is a very inefficient enzyme as it is competitively inhibited by oxygen
63
Q

How much RuBisCO is required for photosynthesis to take place ?

A

A lot of it is needed due to the fact that it is competitively inhibited by oxygen

64
Q

What happens to the unstable 6 carbon compound that is formed in the calvin cycle ?

A
  • It is broken down
  • It forms two 3 carbon Glycerate 3-phosphate (GP) molecules
65
Q

What is each GP molecule converted to ?

A

Converted to another three carbon molecule called triose phosphate (TP)

66
Q

How is TP formed ?

A

Using a hydrogen atom from NADPH and energy supplied by ATP

67
Q

What is triose phosphate ?

A

It is a carbohydrate, a three carbon sugar

68
Q

What happens to the majority of triose phosphate ?

A

The majority of it is recycled to regenerate RuBP so that the calvin cycle can continue

69
Q

What can triose phosphate lead to the formation of ?

A
  • Other carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
70
Q

What are the three steps the calvin cycle can be summarised as ?

A
  • Fixation
  • Reduction
  • Regeneration
71
Q

What is the fixation stage of the calvin cycle ?

A

Carbon dioxide is fixed in the first step

72
Q

What is the reduction stage of the calvin cycle ?

A

GP is reduced to TP by the addition of hydrogen from NADPH

73
Q

What is the regeneration stage of the calvin cycle ?

A

RuBP is regenerated from the recycled TP

74
Q

How many carbon dioxide molecules need to enter the calvin cycle for one glucose molecule to be produced ?

A
  • 6 carbon dioxide molecules have to enter
  • This leads to 6 turns of the calvin cycle
75
Q

How many TP molecules are produced in the process of 1 glucose being produced ?

A
  • 12 TP molecules
  • 2 of which will be removed to make the glucose molecule
76
Q

How many TP molecules are recylced and how many RuBP molecules are regenerated ?

A
  • 10 TP molecules are recycled
  • 6 RuBP molecules are regenerated
77
Q

How many carbons are involved in the production of 1 glucose molecule ?

A

10 x three-carbon TP = 30 carbons shuffled, this gives 6 x five carbon RuBP = 30 carbons

78
Q

What supplies the energy for the regeneration of RuBP ?

A

ATP

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