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B5 > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

what’s light energy converted to and what is it used for?

A

chemical energy which is used to synthesise large organic molecules from inorganic ones like H2O, CO2 (autotrophic nutrition)

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2
Q

what are organisms that photosynthesise called?

A

photoautotrophs

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3
Q

equation for photosynthesis

A

6 CO2 + 6 H2O + energy from photons —-> C6H12O6 + 6 O2

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4
Q

what’s a photon?

A

a particle of light containing energy

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5
Q

What’s the main product of photosynthesis?

A
  • monosaccharide sugar which is converted to disaccharides for transport then starch for storage
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6
Q

photosynthesis is an example of…

A

carbon fixation

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7
Q

do plants respire?

A

YES

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8
Q

what are non-photosynthetic organisms called?

A
  • heterotrophs
  • they obtain energy from digesting organic molecules of food into smaller ones that can be used as respiratory substrates
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9
Q

what type of reaction is respiration ( endothermic/exothermic)?

A

exothermic

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10
Q

respiration equation

A

C6H12O6 + 6 O2 —> 6H2O + 6CO2 + energy

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11
Q

how do photosynthesis and respiration interrelate?

A
  • important in recycling CO2 + O2 in atmosphere
  • products of photosynthesis are the raw materials for aerobic respiration
  • aerobic respiration removes O2 from the atmosphere + adds CO2. Photosynthesis does the opposite
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12
Q

define compensation point

A

when photosynthesis and respiration proceed at the same rate so there’s no net gain or loss of carbohydrate

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13
Q

do plants respire all the time?

A

YES

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14
Q

do plants photosynthesise all the time?

A

NO
- only during daylight
- light intensity must be sufficient to allow photosynthesis at a rate that replenishes carbohydrate stores used up by respiration

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15
Q

define compensation period?

A

time a plant takes to reach its compensation point

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16
Q

how will the compensation period of shade plants differ from that of sun plants?

A

shorter compensation period than sun plants which need higher light intensity to achieve their optimum rate of photosynthesis

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17
Q

what’s the granum (pl. grana)?

A

inner part of chloroplasts made of stacks of thylakoid membranes where light- dependent stage happens

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18
Q

define photosynthetic pigment?

A

pigment that absorbs specific wavelengths of light and traps energy associated with the light whilst reflecting other wavelengths of light (what we see)

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19
Q

define photosystem?

A

funnel shaped system of photosynthetic pigments in thylakoids

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20
Q

define stroma

A

fluid filled matrix

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21
Q

define thylakoid

A

flattened membrane bound sac, contains photosynthetic pigments + photosystems

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22
Q

permeability of outer membrane

A

highly permeable

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23
Q

what are the structures found between grana?

A

intergranal lamellae

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24
Q

what are the 3 different internal compartments and the membranes that create them?

A
  • outer, inner, thylakoid membranes
  • intermembrane space, stroma, thylakoid space
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25
Q

permeability of thylakoid membrane

A

less permeable than outer membrane

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26
Q

why are there many grana and chloroplasts?

A

to provide large SA for:
- photosystems containing photosynthetic pigments that trap sunlight energy
- electron carriers and ATP synthase enzymes needed to convert light to ATP

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27
Q

features of the stroma

A
  • enzymes that catalyse reactions in light dependent stage
  • starch grains, oil droplets, small ribosomes and DNA
  • loop of DNA has genes that code for some proteins needed for photosynthesis to occur which are assembled at chloroplast ribosomes
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28
Q

what are the 2 types of chlorophyll a?

A
  • P680 in photosystem II, peak of absorption is light of wavelength 680nm
  • P700 in photosystem I, peak 700nm
  • both appear blue-green and absorb red light
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29
Q

what colour does chlorophyll b appear?

A

yellow green

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30
Q

name some accessory pigments

A
  • carotenoids
  • xanthophyll
31
Q

define hydrolysis

A

the splitting of a molecule of a molecule using water

32
Q

define dehydration

A

the removal of H from a molecule

33
Q

define metabolic pathway

A

a series of small reactions controlled by enzymes (respiration + photosynthesis)

34
Q

define phosphorylation

A

adding phosphate to a molecule (ADP is phosphorylated to ATP)

35
Q

define photolysis

A

the splitting of a molecule using light energy

36
Q

define decarboxylation

A

removal of CO2 from a molecule

37
Q

define photophosphorylation

A

adding phosphate to a molecule using light

38
Q

define NADP

A

a coenzyme + electron + H carrier

39
Q

define electron carriers

A

molecules that accept e- then donate those e- to another carrier. Form an electron transport system. e.g Ferredoxin, NAD (respiration), NADP(photosynthesis)

40
Q

what are the main stages in the light dependent stage?

A
  1. light harvesting at the photosystems
  2. photolysis of water
  3. photophosphorylation
  4. the formation of NADPH
    O2 produced
41
Q

what’s the role of water in the light dependent stage?

A
  • source of H+ used in aerobic respiration
  • donates e- to chlorophyll to replace those lost when light strikes
  • source of O2 (by-product)
  • keeps cells turgid
42
Q

photolysis equation

A

2 H2O —> 4H+ + 4e- + O2

43
Q

photosystem(s) involved in non cyclic photophosphorylation

A

PS II AND PS I

44
Q

photosystem(s) involved in cyclic photophosphorylation

A

PS I only

45
Q

products of non cyclic photophosphorylation

A
  • ATP
  • O2
  • NADPH
46
Q

products of cyclic photophosphorylation

A
  • ATP in smaller quantities
47
Q

cyclic and non cyclic photophosphorylation involve….

A

electron carriers

48
Q

stages in non- cyclic photophosphorylation

A
  1. photon strikes PS II (P680), its energy is channelled to the primary pigment reaction centre
  2. light energy excites a pair of e- inside chlorophyll molecule
  3. energised pair e- escape from chlorophyll and are captured by e- carriers ( proteins containing Fe cores)
  4. these e- replaced by e- from photolysis
  5. Fe3+ ion reduced when e- accepted to Fe2+. It then donates the e- becoming reoxidised, to the next carrier in chain
  6. during redox reactions, some energy associated with the e- is released and use to pump H+ into thylakoid space from the stroma
  7. eventually, e- captured by another chlorophyll in PS I. These e- replace those lost from PS I due to excitation by light energy
  8. Ferredoxin (protein-Fe-S complex) accepts the e- from PS I and passes them to NADP in the stroma
  9. as H+ accumulate in thylakoid space, electrochemical gradient forms
  10. H+ diffuses down conc gradient through channels in membrane associated with ATP synthase enzymes and, as they do so, flow of protons causes ADP and Pi to re-join ( phosphorylation
  11. as H+ pass through channel, they’re accepted along with e- by NADP which becomes reduced, catalysed by NADP reductase
    - light energy converted to ATP (chemical energy)
49
Q

what products end up in the stroma after photophosphorylation for the lis?

A
  • ATP
  • NADPH
50
Q

Define rate

A

quantity taken up or produced per unit time

51
Q

How can rate of photosynthesis be measured and limitations?

A
  • by measuring the volume of O2 produced per minute by aquatic plant
  • limitations:
    some O2 used in respiration
    dissolved N2 gas collected
52
Q

what’s cyclic and non-cyclic photophosphorylationcalled ?

A

The Z scheme

53
Q

stages in cyclic phosphorylation

A
  1. light strikes PS I, pair of e- in chlorophyll at the reaction centre gain energy + become excited
  2. e- escape and passed on to an e- carrier system and then back to PS I
  3. During passage of e- along system, small amount of ATP is generated
54
Q

what are some differences between cyclic and non-cyclic photophosphorylation?

A
  • no photolysis
  • no H+ or O2 produced
  • no NADPH generated
  • less ATP made
55
Q

why do guard cells only have PS I?

A
  • ATP for active transport of K+ into cells, lowering water potential so that water moves in by osmosis.
  • guard cells swell and stomata open
56
Q

what’s the Calvin cycle?

A

metabolic pathway of the light-independent stage of photosynthesis, occurring (in eukaryotic cells) in the stroma of chloroplasts where CO2 is fixed, with the products of lds to make organic compounds

57
Q

What occurs when there’s no light?

A
  • lis ceases as there’s no ATP and H to reduce carbon and synthesise large complex organic molecules
58
Q

what’s the role of CO2?

A
  • source of C for all organic molecules found in all carbon based life forms on Earth
  • organic molecules used as structures (cellulose cell wall, enzymes, antigens) or as energy stores (starch + glycogen)
59
Q

why is carbon fixation in stroma important for diffusion?

A
  • maintains a conc gradient
  • (air) stomata –> spongy mesophyll –> palisade layer
60
Q

stages of Calvin cycle

A
  1. CO2 combines with ribulose bisphosphate RuBP ( 5 C, CO2 acceptor), catalysed by RuBisCO
  2. RuBP accepts the carboxyl (COO-) group, becomes carboxylated forming an unstable 6C intermediate compound that immediately breaks down
  3. product is 2 GP (glycerate-3-phosphate) (3C), CO2 has been fixed
  4. GP is reduced, using H+ from NADPH to triose phosphate (TP). Energy from ATP is also used at the rate of 2 ATP for every CO2 molecule fixed during stage 3
  5. in 10 of every 12 TP molecules (3C), the atoms are rearranged to 6 RuBP (5C) which requires phosphate groups.
    - the remaining 2 of the 12 TP are the product
61
Q

why do plants contain little RuBP?

A

its converted to GP which is continually being regenerated

62
Q

how many turns of the Calvin cycle are needed to make 2TP (to make one glucose molecule)

A

6

63
Q

Outline the main processes in the Calvin cycle

A
  1. Carbon fixation (RuBP combining with CO2 to form GP)
  2. Reduction (of GP to TP)
  3. Regeneration ( TP to RuBP)
64
Q

why is RuBisCo only activated during daylight?

A
  • H+ pumped from stroma into thylakoid space in lds raises pH to 8 which is optimum for RuBisCO
  • extra ATP in stroma also activate it
  • in daylight Mg2+ ions in stroma increase which are cofactors
  • Ferredoxin that’s reduced by e- from PS I activates enzymes used in Calvin cycle
65
Q

what are the uses of TP

A
  • synthesis of aa, fatty acids, glycerol
  • some glucose converted to sucrose, starch, cellulose
  • the rest us recycled to regenerate RuBP. 5TP (3C) form 3 RuBP (5C)
66
Q

What’s water stress?

A

condition a plant faces when water supply becomes limited

67
Q

What’s a limiting factor?

A

the factor that will limit the rate when its at lower levels

68
Q

examples of limiting factors

A
  • CO2 conc
  • H20
  • light intensity
  • availability of chlorophyll, e- carries, relevant enzymes
  • Temperature
  • turgidity of cells
69
Q

How does light intensity affect rate of ps?

A
  • light provides energy for lds to produce ATP + NADPH
  • causes stomata to open for gaseous exchange which causes transpiration (increase H2O uptake)
  • at constant favourable temp + CO2 conc, light intensity is the limiting factor but as it increases rate of ps increases until another factor becomes the limiting factor
70
Q

How does temperature intensity affect rate of ps?

A
  • enzyme catalysed reactions sensitive to temp
  • 25-30C, rate of ps increases as temp increases ( if other factors are at sufficient levels)
  • above 30C, growth rates reduce due to photorespiration: O2 competes with CO2 for RuBisCO’s active site
  • above 45C, enzymes denature so conc of GP + TP reduce and RuBP not regenerated
71
Q

What happens to levels of RuBP, TP, GP if there’s little or no light?

A
  1. GP can’t be reduced to TP (GP increases)
  2. TP levels fall + GP accumulates
  3. if TP levels fall, RuBP can’t be regenerated
72
Q

What happens to levels of RuBP, TP, GP if there’s little or no CO2?

A
  • RuBP can’t accept CO2 (to form GP) and accumulates
  • GP can’t be made
  • so TP can’t be made
73
Q

what happens when a plant is under stress?

A
  • water lost via transpiration not replaced
  • cells become plasmolysed
  • roots produce abscisic acid which is translocated to leaves + closes stomata
  • tissue becomes flaccid + leaves wilt
    -rate of ps decreases
74
Q

How to set up and use a photosynthometer ( Audus microburette)

A
  • set up so its airtight + no bubbles in capillary tubing
  • gas collected at flared end of capillary tube over a known time period
  • gas bubble can be moved into the part of the tube against the scale and its length is measured
  • if radius of tube bore is known :
    volume of gas collected = length of bubble x (pi)r2

B5 (8 decks)

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