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Plant Science > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

What are Plastids ?

A

Are the site of manufacture and storage of important chemical compounds used by some cells. They comprise a variety of types which all play a central role in cellular function in different ways depending on plastid type and cell type

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2
Q

Are chloroplats a type of plastid ?

A

Yes

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3
Q

Whats the function of the chloroplasts, amyloplasts, chromoplasts, elaioplasts, etioplasts and proplastids?

A

CHLOROPLASTS = photosynthesis

AMYLOPLASTS = storage of starch

CHROMOPLASTS = accumulation of pigments

ELAIOPLASTS = lipid storage plastids

ELTIOPLASTS = plastids which develop in the dark

PROPLASTIDS = originator of all plastids.

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4
Q

Where would you find chloroplasts on a plant ?

A

Stem tissue
Fruit tissue
Seed tissue might all be capable of photosynthesing

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5
Q

What is the chloroplast the site of and name the 4 major structures of it ?

A

Its the site of photosynthesis
The 4 main structures are the
1- Pair of outer limiting membranes - ENVELOPE
2- Unstructured background matrix - STROMA
3- Highly structured internal system of membranes - THYLAKOIDS
4- Intra-thylakoid space - LUMEN

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6
Q

What are thylakoids associated into ?

A

into granal stacks interconnected by single thylakoids

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7
Q

Whats the structure of thylakoids and how is it connected to grana ?

A

Provides a network of interconnections between grana.
Contains chlorophyll and carotenoid pigments
Site of light dependent energy conserving reactions of photosynthesis

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8
Q

Where does photosynthesis takes place ?

A

Takes place in the chloroplasts within mesophyll cells in plants

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9
Q

Whats the space within the thylakoid membrane ?

A

called the lumen

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10
Q

Whats the space surrounding the thylakoid membrane ?

A

The stroma

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11
Q

What are the 4 major protein complexes of photosynthetic electrons and proton transfers ?

A
  1. Photosystem 11
  2. Photosystem 1
  3. Cytochrome b6f complex
  4. ATPase
    in appressed (stacked) or non-appressed (unstacked ) regions
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12
Q

what is light captured by in a plant ?

A

Light is captured by chlorophylls and carotenoids, which are proteins in the thylakoid membrane complexes.

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13
Q

What light do chlorophylls and carotenoids absorb?

A

CHLOROPHYLLS = dominant pigment absorbing red and blue light
CAROTENOIDS = Accessory pigments absorb blur light strongly to help trap more energy

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14
Q

Why is it plants are green ?

A

We see the portions of the visible spectrum not absorbed by pigments, so plants are green because of chlorophyll. They contain a lot of it ! . As it absorbs in the blue and red parts of the visible spectrum, it is reflecting the green which is what we see.

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15
Q

How can we measure absorption in the lab ?

A

On a spectrophotometer. You will see other accessory pigments absorbing at different wavelnengths. These serve to capture light energy and trasnfer this to the chlorophyll.

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16
Q

What is visible light ?

A

Is a part of the electromagnetic spectrum and can be considered as a wave which comes in packets called quanta or photons.

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17
Q

What is the energy content of quanta inversely related to ?

A

Energy content of quanta is inversly related to wavelength - the longer the wavelength the less the energy

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18
Q

What is irradiance ?

A

Since light has a spatial quality, measurements of light can be expressed per unit area , thus light energy can be measured as watts.msquared, this term is called irradiance

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19
Q

What wavelengths do carotenoids absorb ?

A

Absorb blue light at wavelengths that dont absorb chlorophyll too well and pass energy to chlorophyll at the base of photosystem

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20
Q

What are the 4 ways you can measure light ?

A

1- Photon Flux Density (PFD)
2- Photon number ( mol )
3- Photon flow (mol s -1 )
4- Photon fliux or photon irradiance ( mol m-2s-1)

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21
Q

What can cause light to damage photosystem 11 ?

A

In high conditions excessive formation of Ch1-1 or p680 can easily damage photosystems especially ps11

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22
Q

What visible light is visible to the human eye ?

A

Within the electromagnetic spectrum

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23
Q

Do short tight waves or long wide waves carry more energy ?

A

Short tight waves carry more energy, long wide waves carry less energy

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24
Q

How can we measure the amount of energy of a wave ?

A

By measuring its wavelength

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25
Q

What do pigments such as chlorophyll and carotenoids do to light ?

A

Pigments such as chlorophyll and carotenoids absorb and reflect light at certain regions of the electromagnetic spectrum.

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26
Q

What can plant pigments only do between 700nm and 400nm ?

A

Absorb only light between 700 nm and 400nm.

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27
Q

What region does chlorophyll a absorb light and chlorophyll b ?

A

Chlorophyll a absorbs light in the blue-green violet region, chlorophyll b absorbs red-blue light

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28
Q

What region does carotenoids absorb light in and what colour wavelengths do they reflect ?

A

Carotenoids absorb light in the blue -green and violet region, reflect yellow red and orange wavelengths.

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29
Q

What is a redox reaction ?

A

Wheres electrons are transferred between molecules.

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30
Q

What is oxidation and reduction in terms of electrons ?

A

Oxidation is loss of electron
Reduction is gain of electrons

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31
Q

What occurs when photosystem 11 and 1 absorb photons ?

A

A photon of the right amount of light energy is absorbed by a pigment
The extra energy causes an electron to rise from its ground state and the excited state.
(The electron goes to a higher energy level, but is unstable )
The pigment then needs to get rid of this energy to return to the ground state

32
Q

How is light funelled to the reaction centre ?

A

Energy is transferred randomly to pigments that absorb light of increasingly longer wavelengths until the energy reaches the reaction centre chlorophyll in photosystem 11, which transfers an excited electron to a primary electron acceptor.

33
Q

Where is PS11 located ?

A

is located on the inside of the thylakoid membrane

34
Q

What reaction does PS11 help take place ?

A

ps11 is a multi protein complex which contains magnase and uses the enormous energy generated from charge seperation to carry out the reaction
2H20——02 + 4H+ + 4e-

35
Q

What occurs across the membrane ?

A

The protons are formed on the inside of the thylakoid membrane and thus contribute to building a pH gradient in proton concentration across the membrane

36
Q

What is electrons used for in PS11 ?

A

The electrons are used to reduce the core of PS11

37
Q

What is the light-driven photosynthetic electron transport ?

A

As a result of light capture by chlorophyll, electrons are moved along through a series of different molecules. This process is called light-driven photosynthetic electron transport.

38
Q

How is the source of electron at the start of the chain broken down ?

A

The source of electrons at the start of the chain are water molecules which are broken down using light energy.

39
Q

Explain the steps in the PS1 reaction centre to produce ATP ?

A

1- Light absorbed by ps1 excites electrons in the reaction centre chlorophyll which are then donated to an electron acceptor, FERRODOXIN
2- FERRODOXIN can then transfer electrons to be stored by the high energy molecule NADPH which in turn can be used to be stored by the high energy molecule NADPH.
3- Consequently, the result of all this electron transport is high energy molecules of NADPH and a proton concentration gradient across the membrane
4- The protons flow back down the gradient through the ATP synthase complex in much the same way as in the mitochondria to generate ATP. The whole process of ATP generation is called OXIDATIVE PHOSPHORYLATION.

40
Q

What are the two processes used to increase the concentration of protons in the thylakoid lumen so oxidative phosphorylation can occur ?

A

1- Proton Pump
2- Photolysis on the thylakoid lumen

The protons flow back down the gradient through the ATP synthase complex in much the same way as in the mitochondria to generate ATP. The whole process of ATP generation is called OXIDATIVE PHOSPHORYLATION

41
Q

What is the two fold result of this light powered electron transport down an energy gradient ?

A

1- The high energy molecule NADPH is produced which is used in a wide variety of biochemical reactions which need an input of energy
2- The creation of a conc gradient of protons across the membrane is utilised by the ATP synthase complex which allows protons to flow through it out into the stroma down the conc gradient and at the same time it synthesises ATP

42
Q

How fast does it take for the ATP and NADPH to be used up after being formed ?

A

VERY FAST - consumed by stromal reactions almost immediately

43
Q

What does the chloroplast contain where the photosynthetic light reaction occurs at ?

A

The chloroplast contains thylakoid membranes where the photosynthetic light reaction occur

44
Q

What are the 4 main protein complexes of the thylakoid membrane ?

A

PS11
Cytochrome b6f
PS1
ATP synthase

45
Q

How is light energy ( photons ) converted to chemical energy ?

A

By special chlorophyll molecules on PS11 and PS1 by driving high energy electrons through the electron transport chain.

46
Q

What do the electrons reduce NADP+ to ?

A

NADPH

47
Q

What does the energy from light absorption drives electrons from ?

A

From water splitting on the lumen side of the thylakoid membrane of PS11

48
Q

How is NADPH produced ?

A

PS11 AND PS1 generate a proton gradient and produce NADPH

49
Q

What does the proton gradient do to the ATP synthesis ?

A

Drives the ATP synthesis

50
Q

What step is NADPH and ATP required for in photosynthesis ?

A

required for the CALVIN CYCLE

51
Q

What does the light dependent produce ?

A

Produce ATP, NADP

52
Q

What are ATP and NADPH used to make from CO2 ?

A

ATP and NADPH are used to make sugars from CO2

53
Q

What occurs during the fixing of carbon ?

A

fixing co2 and processing the products requires input of energy for which the high energy molecules arising from light energy absorption on the thylakoid membrane are used - ATP AND NADPH
2- CO2 is fixed into carbohydrates via the calvin benson cycle
Which consumes the ATP and NADPH produced from the light reactions and regenerates ADP, Pi and NADP

54
Q

What occurs in the calvin cycle ?

A

C02 is fixed using the enzyme RUBISCO and the resulting molecules are processed in a series of enzyme driven reactions which function in a cyclical manner.
The cycle generates more molecules to react with C02 and molecules with 3 carbon atoms, some of which are used as the first step in making sugars and starch

55
Q

What molecules was found out by RADIOISOTOPE EXPERIMENTS into which C02 was incorporated with ?

A

3-phosphoglycerate

56
Q

What reaction is carried out by RUBISCO to produce two molecules of 3-phosphoglycerate ?

A

Carbon dioxide reacts with a 5-carbon sugar ( ribulose-1-5-bisphosphate ) to form an unstable six arbon intermediate which rapidly splits to give two molecules of the 3 carbon compund 3 - phosphoglycerate

57
Q

What are the three steps of the Calvin Cycle ?

A
  1. CARBON FIXATION - The enzyme Rubisco incorporates C02 into an organic molecule, 3-pga
  2. REDUCTION OF 3-PGA - 3-PGA is reduced using electrons supplied by NADPH
  3. REGENERATION OF RuBP - RuBP that starts the cycle is regenerated, so the cycle can continue. One CO2 is incorperated at a time, so the cycle must be completed three times to produce a single three carbon GA3P molecule and 6 times to produce a 6C glucose molecule.
58
Q

What do each C02 fixed requires ?

A

3 ATP and 2 NADPH

59
Q

What is RUBISCO made up of ?

A

Is made up of 8 large subunits (plastid encoded) and 8 small subunits ( nuclear encoded)

60
Q

Is rubisco a carboxylase or an oxygenase ?

A

Both, the calvin cycle uses C02

61
Q

What occues to RuBP in photorespiration ?

A

Rubisco oxygenates RuBP, producing one 3-PGA and one 2-PG and is known as photorespiration.

62
Q

What is the process of photorespiration ?

A

It uses oxygen instead of carbon dioxide - Instead of fixing carbon dioxide into a complex sugar, the plant has made phosphoglycolate , a nearly useless compound, which must be recycled in a process known as photorespiration.

63
Q

How does photorespiration reduce efficiency of photosynthesis ?

A

Photorespiration occurs about 25 percent of the time over carboxylation in C3 plants

64
Q

Why was the photorespiration cycle evolved ?

A

To recover the carbon wasted during the oxygenase reaction which produces phosphoglycolate

65
Q

What fixation occurs when the oxygenase reaction completes in photorespiration ?

A

The oxygenase reaction completes with the fixation of C02 at the active site adding oxygen to RuBP instead of C02

66
Q

What changes with the oxygenase activity of RUBISCO as temps rise ?

A

As temperatures rise, the oxygenase activity of RUBISCO increases relative to the carboxylase activity

67
Q

Is RUBISCO a slow enzyme ?

A

YES

68
Q

Whats it called when rubisco fixes carbon ans what does it produce?

A

RUBISCO can fix carbon as a carboxylase, producing 3xPGA

69
Q

Whats it called when RUBISCO fixes oxygen and what does it produce ?

A

RUBISCO can fix oxygen which is called photorespiration, producing 1 x 3-PGA and 1 x PG

70
Q

What plants does photorespiration occur in ?

A

Photorespiration competes with carboxylation and occurs about 25 percent of the time in C3 plants - reducing the efficiency of photosynthesis

71
Q

What is the overall products of the calvin cycle ?

A

6CO2, 18ATP, 12 NADPH and 12H20

72
Q

The pentose sugar Ribulose 1,5 bisphosphate joins with C02 what does it then give when it leaves ?

A

It gives two molecules of 3-phosphoglycerate

73
Q

Whats the name of the enzyme that carries out the first step of the calvin cycle ?

A

Is called RUBISCO

74
Q

What is used to convert 3-phosphoglycerate to glyceraldehyde 3-phosphate ?

A

Energy in the form of NADPH and ATP from the electron transfer reactions

75
Q
A

Plant Science (7 decks)

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