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Biology🧬 > Photosynthesis☀️ > Flashcards

Photosynthesis☀️ Flashcards

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1
Q

Symbol equation for photosynthesis

A

6CO2 + 12H2O
——>
C6H12O6 + 6O2 + 6H2O

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2
Q

What is the light dependent stage? (simple)

A
  • Formation of ATP by photophosphorylation and reduction of NADP
  • Water is broken down into hydrogen and oxygen
  • Using light energy - only occurs in light
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3
Q

What is the light-independent stage? (Simple)

A

•Hydrogen reacts with carbon dioxide
-forms a carbohydrate
-water is reformed
•Occurs both in light and dark

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4
Q

What is the stroma?

A
  • Chloroplast matrix

* Contains ribosomes, circular DNA and enzymes used for photosynthesis

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5
Q

What is the chloroplast envelope?

A

Double membrane (permeable)

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6
Q

What are thylakoids?

A
  • Membrane sacs suspended in stroma

* Contain chlorophyll

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7
Q

What’s the granum?

A
  • Stack of thylakoids

* Connected by intergranal lamella

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8
Q

Where are ribosomes found in a plant cell?

A

The stroma

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9
Q

What are starch grains?

A

Insoluble storage product of photosynthesis (carbohydrate)

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10
Q

What is a lipid droplet?

A

Energy store made from sugars produced during photosynthesis

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11
Q

What is the thylakoid space?

A

Continuous fluid-filled compartment connecting thylakoids in a stack

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12
Q

Why is it important that chloroplasts form compartments in the plant cell?

A

To isolate the photosynthetic reactions from other cellular activities

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13
Q

What is the wave model?

A
  • Light is a wave

* Describes how light passes through space and how it is absorbed by photosynthetic pigments

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14
Q

What is the particulate model?

A
  • Light is particles

* Used when explaining the events in photosynthesis

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15
Q

What is the main photosynthetic pigment?

A

Chlorophyll

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16
Q

What is the structure of chlorophyll?

A
  • Porphyrin ring
  • Magnesium centre
  • Linked to a long hydrocarbon chain
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17
Q

What is chlorophyll a?

A
  • Common to all plants, algae and Cyanobacteria that photosynthesise
  • Absorbs light mainly in red and blue parts of the spectrum
  • Only pigment that takes a direct part in photosynthesis
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18
Q

What is bacterio-chlorophyll?

A
  • Some bacteria

* Maganese instead of magnesium

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19
Q

What is the function of pigments?

A
  • Absorb some wavelengths of light and reflect others

* Transfers light energy into chemical energy

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20
Q

What are accessory pigments?

A

•Do not participate directly in the light-dependent stage
•Light harvesting pigments
•Broaden range of light wavelengths a plant can use
-absorb wavelengths outside of chlorophyll a and convey the beefy to chlorophyll a
•Includes carotenoids and other chlorophylls

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21
Q

What is the absorption spectrum?

A

Displays the wavelengths of light that a particular photosynthetic pigment absorbs

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22
Q

What is the action spectrum?

A

Displays the wavelengths of light that bring about photosynthesis in a particular plant

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23
Q

Describe the action/absorption relationship

A
  • Absorption spectrum of the combined photosynthetic pigments in a plant coincides closely with the action spectrum of photosynthesis for that plant
  • Supports notion that these pigments harvest light for photosynthesis
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24
Q

How does chlorophyll harness energy from sunlight?

A

•When a chlorophyll molecule absorbs a photon of light, one of the pigments electrons gains energy
•The energy level is raised to an excited state (from ground state)
•The excited electron is passed on to an electron acceptor and passed along the ETC
-electron acceptor is reduced - gains e-
-chlorophyll is oxidised - loses e-

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25
Q

What is a photosystem?

A
  • Photosynthetic pigments are arranges in clusters embedded in the thylakoid membrane
  • Antenna complex contains accessory pigments
  • Reaction centre contains chlorophyll a
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26
Q

What is photosystem I?

A

Reaction centre is called P700

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27
Q

What is photosystem II?

A

Reaction centre is called P680

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28
Q

What is chromatography?

A

•Separating molecules from a mixture
•Different molecules have differing solubility in particular solvents
•Pestle and mortar used to obtain extract of photosynthetic pigments
•Concentrated spot applied to origin of chromatogram
•Chromatogram placed in solvent
-molecules separate according to solubility/molecular mass (more soluble/lighter move further)

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29
Q

What are Rf values?

A
  • Once the molecules have been separated by chromatography, they can be identified by calculating their Rf value
  • Specific to each molecule
  • Compares distance travelled by molecule with that of the solvent
  • Always less than 1
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30
Q

What is the Rf calculation?

A

Rf =
Distance travelled by molecule/
Distance travelled by solvent front

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31
Q

What is photosynthesis?

A
  • Light energy from the sun is transformed into chemical potential energy
  • Used to synthesise large organic molecules from inorganic substances
  • Then available to consumers and decomposers
32
Q

Explain how respiration in plants and animals depends upon the products of photosynthesis

A
  • Plants need glucose to convert to starch

* Animals need O2 for respiration

33
Q

Describe the Z scheme (light dependent stage)

A

•Photosynthetic pigments in antenna complex of PS2 absorb light energy
-energy is transferred to reaction centre, where it excites an electron in the chlorophyll a molecules
•Excited electrons are boosted to a higher energy level and leave the chlorophyll a molecule to be received by an electron acceptor
-oxidises chlorophyll a, reduces electron acceptor
•Electrons are passed along the ETC in a series of redox reactions to PS1
-energy lost by electrons is used to carry out photophosphorylation
•Light absorbed by PS1 boosts 2e- to a higher energy level
-electrons are received by another electron acceptor
•Photolysis of water produces 2e- which replace those lost from PS2, oxygen (waste) and 2H+
•2H+ and 2e- reduce NADP

34
Q

What is the photolysis of water?

A
  • 2e- replace those lost from PS2

* Loss of electrons causes water to dissociate into 2e-, 2H+ and 1/2O2

35
Q

What is the chemiosmotic theory of photophosphorylation?

A

•As electrons pass along the ETC, they release energy
-this energy pumps protons from the stroma across the thylakoid membrane and into the thylakoid space
•Protons accumulate, forming a steep electrochemical/proton gradient between the thylakoid space and the stroma
•Protons diffuse back into the stroma through the chemiosmotic protein channels where ATP sythase is located
-flow of protons provides energy to produce ATP from ADP and Pi

36
Q

Describe the process of light energy being converted into chemical energy (very detailed)

A
  • Chloroplasts are energy transducers and convert the energy of light photons into ATP
  • Chlorophyll and other pigments are embedded in the thylakoid membrane
  • Large surface area to absorb light
  • Pigment molecules are arranged in an antenna complex called photosystem
  • Different pigments absorb different wavelengths of light
  • Accessory pigments transfer the energy down to the reaction centre with chlorophyll a molecules
  • P700/PS1 and P680/PS2
  • Chlorophyll absorbs red and blue regions
  • Excited chlorophyll a molecules emit electrons
  • Green light is reflected
  • Light energy is therefore converted to chemical energy
37
Q

Describe the process of the Z scheme (very detailed)

A

•In non-cyclic photophosphorylation, PS2 has electrons boosted from their ground state to an excited state
•Excited electrons pass to electron acceptors, reducing them, leaving the chlorophyll a molecules oxidised
•Electrons are passed along ETC in thylakoid membrane to PS1
•Releases energy and ATP is produced
•Excited electrons are emitted from PS1, reducing an electron acceptor, which pass an electron to oxidised NADP, reducing it
•Each NADP receives 2 e- and picks up 2H+ from the stroma to become reduced NADP
•Light causes photolysis of water which
-provides 2e- to replace those lost by PS2
-provides H+ to combine with electrons from PS1 to reduce NADP
-produces oxygen, which is released as a waste
•Cyclic photophosphorylation involves PS1
•Only ATP produced from cyclic
•ATP and NADPH2 produced from non-cyclic

38
Q

How are gradients maintained?

A
  • Photolysis of water increases the H+ concentration

* Reduction of NADP decreases the H+ concentration

39
Q

Where does photolysis of water occur?

A

Thylakoid space

40
Q

Where does the reduction of NADP occur?

A

Stroma

41
Q

What is non-cyclic photophosphorylation?

A

Electrons from chlorophyll a molecules in PS1 are used to reduce NADP and are replaced indirectly by electrons from the photolysis of water

42
Q

What is cyclic photophosphorylation?

A
  • Electron acceptor at PS1 is at the highest energy state

* It is possible for some of these excited electrons to return to the chlorophyll a molecule in PS1 via the ETC

43
Q

What is the electron donor for both cyclic and non-cyclic photophosphorylation?

A

Chlorophyll a in PS1

44
Q

What is the terminal electron acceptor in non-cyclic photophosphorylation?

A

NADP

45
Q

What is the terminal electron acceptor in cyclic photophosphorylation?

A

Chlorophyll a in PS1

46
Q

What are the products of non-cyclic photophosphorylation?

A
  • ATP
  • NADPH2
  • Oxygen
47
Q

What is the product of cyclic photophosphorylation?

A

ATP

48
Q

What is the light independent stage/Calvin cycle? (Simple)

A

ATP and NADPH2 are used to reduce CO2 to triose phosphate

49
Q

Why does the Calvin cycle take place in the stroma?

A

This is where the enzymes involved are located

50
Q

Describe the Calvin cycle?

A

•Carbon fixation
-CO2 {1C} combines with ribulose bisphosphate (RuBP) {5C}
-catalysed by enzyme rubisco
-carboxylation reaction
•Forms 2x glycerate 3 phosphate (GP) {3C}
•NADPH2 is used to reduce 2x GP to 2x triose phosphate (TP) {3C}
-hydrolysis of ATP provides energy for this reaction
•5/6 TP is converted by a series of reactions, via ribulose phosphate, into RuBP
-ATP provides phosphate and energy required
•1/6 TP is converted rapidly to glucose and other carbohydrates, amino acids, lipids, nucleic acids

51
Q

Where does the ADP and NADP go after they are used in the light independent stage?

A

They return to the light dependent stage

52
Q

What is carboxylation?

A

Addition of carbon dioxide

53
Q

How does light intensity affect the rate of photosynthesis?

A

•As light intensity increases, so does the rate of photosynthesis
-light is limiting factor
•Plateau - no further increase in rate so light is no longer the limiting factor

54
Q

How does carbon dioxide affect the rate of photosynthesis?

A
  • If there are no other limiting factors, an increase in CO2 concentration will increase the rate of photosynthesis
  • Some concentrations can damage leaves
  • Low levels of CO2 limit photosynthesis
55
Q

How does temperature affect the rate of photosynthesis?

A

•Little affect on light-dependent stage
•Calvin cycle involves enzymes, and also involves membranes (chemiosmosis)
-optimum temperature

56
Q

What are some other limiting factors?

A 
•Chloroplast concentration
•Magnesium
•Concentration of rubisco 
•Water 
-guard cells
-photolysis
57
Q

What is the law of limiting factors?

A
  • The rate of any physiological process will be limited by the factor that is in shortest supply
  • Any change in level of a limiting factor will affect the rate of photosynthesis
58
Q

Why is magnesium needed?

A

To synthesise chlorophyll

59
Q

Why is nitrogen needed?

A

To synthesise amino acids, nucleic acids and chlorophyll from TP

60
Q

Explain a graph where:
•In bright light, RuBP and TP are high and GP is low
•In dim light, GP is high and RuBP and TP are low

A 
•High rate of light dependent reaction 
-more NADPH2 and ATP produced
-more GP converted to TP
-more RuBP regenerated from TP 
•Not enough ATP and NADPH2 (limiting factor) to turn GP into TP and regenerate RuBP
61
Q

Explain a graph where:
•In high CO2 concentrations, GP and TP are high and RuBP is low
•In low CO2 concentrations, RuBP is high GP and TP are low

A 
•More CO2 fixed by RuBP 
-more GP produced
-RuBP is used more quickly
-more GP so more TP can be made
•Less CO2 fixed by RuBP 
-so RuBP accumulates 
-GP not produced so TP can’t be made
62
Q

How would a lack of magnesium affect the rate of photosynthesis?

A
  • Reduce rate
  • Magnesium is used to synthesise chlorophyll
  • Chlorophyll is required to absorb red and blue wavelengths of light to carry out light-dependent reactions
  • Less electrons emitted
  • Less ATP and NADPH2 produced for light independent stage
  • Less GP converted to TP
  • ALSO magnesium is a cofactors of rubisco, so less carbon fixation
63
Q

How would a lack of water in the soil affect the rate of photolysis?

A 
•Reduce rate
•Less water absorbed for photolysis
•Less hydrogen used to reduce NADP
•Less electrons to replace those lost
•ALSO less CO2 for light independent stage 
-stomata close
64
Q

How would a herbicide blocking electron flow affect the rate of photosynthesis?

A 
•Reduce rate
•Electrons can’t be transported to PS1 along the ETC
•No energy released from redox reactions
-protons cannot be pumped 
•Cyclic reactions cannot occur 
-less ATP 
•Non-cyclic reactions cannot continue
-less NAPDH2 and ATP
•Less GP converted into TP
65
Q

Describe the Hill reaction

A 
•Chloroplasts are isolated from plant cells and exposed to light
•Prepared in an ice cold sucrose buffer
-slows down enzyme reaction
-sucrose affects osmosis
-buffer keeps same pH to preserve enzymes
•Electrons releases during light-dependent stage are picked up by blue electron acceptor DCPIP
•If left in dark won’t decolourise 
-light dependent reaction will not work
-no electrons emitted to reduce ATP 
•If boiled won’t decolourise
-proteins in membrane denature
-membrane bilayer disrupted
66
Q

Fully describe a light intensity graph

A

•As light intensity increases, so does rate of photosynthesis
-light intensity is limiting factor as it limits rate of light dependent stage of photosynthesis
•When the rate reaches a maximum, the graph plateaus and light has no further effect
-this is because light is no longer a limiting factor
-something else becomes a limiting factor

67
Q

How can light affect the light independent stage?

A

•More stomata open
-more CO2 available to be fixed during Calvin cycle
•Increased Mg ions in stroma (co-factor of rubisco)
•More NADP reduced
-activates enzymes of Calvin cycle

68
Q

What are limitations of counting bubbles technique?

A
  • Could miscount bubbles

* Bubbles could be different sizes

69
Q

What improvements could be made to the counting bubbles technique?

A

Measure volume of O2

-use gas syringe/upside down burette

70
Q

What are the control variables of the counting bubbles technique?

A 
•Light intensity 
•Temperature 
-heat shield on lamp/LED lamp
•Carbon dioxide concentration 
-sodium hydrogen carbonate in water
71
Q

What would happen if 6 molecules of CO2 entered the Calvin cycle?

A
  • 12 molecules of TP

* 2 molecules leave cycle and combine to form one molecule of glucose

72
Q

What is the closest way of controlling internal factors, such as concentrations of chlorophyll and rubisco?

A
  • Choosing plants of the same species, same age, with the same number of leaves
  • Impossible to control internal factors
73
Q

What causes leaf discs to rise in a leaf disc experiment?

A

•Carry out photosynthesis
•Produces oxygen
•Gas, so increases buoyancy
-fills air spaces

74
Q

Why would a dark leaf photosynthesise more than a light green leaf?

A
  • Contain more photosynthetic pigments (chlorophyll a)
  • More light energy absorbed
  • More light dependent stage
  • More photolysis of water
  • Increased rate of oxygen production
75
Q

How could you investigate the effect of light wavelength on photosynthesis?

A 
•Red and blue filter 
-absorb wavelengths on red and blue end of spectrum 
-high rate of photosynthesis 
-more oxygen production 
-(leaf discs would rise)
•Green filter
-only green light allowed in, cannot be absorbed 
-no photosynthesis 
-(leaf discs wouldn’t rise)
•Black filter
-no light 
-light dependent reactions can’t occur
-(leaf discs wouldn’t rise)
76
Q

What effect would a substance that blocks the electron carrier binding site of PS2 have? And why would a plant die?

A

•Stops electrons being transported to PS1 from PS2 along ETC
•Blocks reduction of ATP
•Doesn’t affect cyclic photophosphorylation because electrons return to ETC
DIE BECAUSE
•Can’t generate NADPH2 & ATP as electron flow from PS2 is blocked
•Calvin cycle can’t occur
-growing part of the plant will not have glucose for respiration

77
Q

Apart from chlorophyll a, name three other pigments you would expect to be present in a photosystem

A
  • Chlorophyll b
  • Carotenoids
  • Xanthophyll

Biology🧬 (24 decks)

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