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A2 Bio > C13: Photosynthesis > Flashcards

C13: Photosynthesis Flashcards

1
Q

define photosynthesis

A

process by which light energy is captured by chorophyll pigments and converted to chemical energy of organic molecules

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2
Q

differentiate between photo and chemo autotrophs

A

-photo ones (green) depend of light energy
-chemo ones (nitrifying bacteria) depend on chemical sources
to make their own food

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3
Q

what happens in photosynthesis over all

A

CO2 is fixed and reduced to carbohydrate using hydrogen from water

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4
Q

where are pigments found and how are they arranged

A
  • in chloroplast

- light harvesting clusters PSI and PSII

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5
Q

what are the 2 types of pigment, examples, and what makes them different

A

primary- chlorophyll a and b, absorb red and blue-violet
accessory- beta carotenoids and xanthophyll, absorb blue-violet
they absorb different wavelengths

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6
Q

what is a photosystem and where is it found

A
  • chlorophyll molecules ie pigments grouped together

- thylakoid membrane of grana

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7
Q

state importance of accessory pigments

A
  • prevent photooxidation of chlorophyll

- max utilization of all wavelengths of light ie energy funneled to primary pigment

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8
Q

what are 2 types of photosystems

A

-PSI: reaction centre activated by 700nm
-PSII: reaction centre activated by 680nm
occur simultaneously

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9
Q

what is the absorption spectrum of chlorophyll

A
  • measure of how much of each wavelength chlorphyll absorb s
  • blue and red most strongly, others are less or 0
  • absorption depends on chemical structure of chlorophyll
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10
Q

what is the action spectrum of chlorophyll

A
  • what wavelength brings about photosynthesis and which gives highest rate
  • blue and red give highest rate of
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11
Q

how is action specturm discovered

A

different wavelength projected for some unit time on aquatic plant and volume of o2 released is measured to calculate rate of photosynthesis

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12
Q

use of chromatography in this chapter and how to find Rf value

A
  • see what pigments are present

- distance travelled by pigment/distance travelled by solvent

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13
Q

state relative Rf values of the 3 pigments

A

Carotenoids has close to 1
Chlorophyll b has lowest
Chlorophyll a has in between these

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14
Q

briefly state adaptations of leaf for photosynthesis 7

A
  • minimal overlap to reduce shade
  • large surface area and face sun perpendicular for max area to get light
  • thin so both top and bot layers can phosyn
  • transparent cuticle and epidermis to allow light to reach mesophyll
  • palisade cells along with chloroplats for max light trapping
  • palisade arranged in layer to trap most light
  • chlorplasts can move to arrange in best absorbing position
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15
Q

briefly state adaptations of chloroplast for photosynthesis 4

A
  • double membrane permeable to o2,co2, atp, sugars and other phosyn products
  • photosystems with cholophyll in grana thylakoid membrane to maximise absorption area
  • thylakoid spaces restricted for accumulation of H+/build gradient
  • fluid stroma is site for the many enzymes
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16
Q

structure of chloroplast; size, arrangement of thylakoid membrane, chlorophyll presense

A

4-10Mm long
2-3Mm wide
flat dis shaped piles called grana
cholorophyll molecules in thylakoid/grana membrane

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17
Q

what is the light dep reaction and where does it occur

A

photochemical step of phosyn

in grana

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18
Q

Describe step 1 PSII of non cyclic phosphorylation

A

-680nm excites a pair of e- at PSII chlorophyll molecule which rises to higher state and caught by an e- acceptor. oxidised chlorophyll therefore photolyses H2O to get back ground state electrons. H2O->2H++2e-+1/2O2. initial electron pair moves downhill via series of redox and releases energy/ATP. this is used to pump H+ from stroma into thylakoid thus gradient
(all this happens in the thylakoid membrane)

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19
Q

Describe step 1 PSI of non cyclic phosphorylation

A

-700nm excites electrons which are caught by acceptors and as they move downhill ATP forms, which is used to form NADP + H+ in stroma. the vacated space is filled by e- from PSII which have fallen to ground state

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20
Q

Describe step 2 (general not PS) of non cyclic phosphorylation and end result

A
  • using the proton gradient created by PSII, H+ flow back into stroma throug pore in ATP synthase and release energy for chemiosmosis/ATP forming
  • ATP and NADPH pass into stroma for light indep reactions hence dont acculumulate
21
Q

why does cyclic phosphorylation occur

A
  • co2 conc in leaf becomes low
  • so co2 fixation slows
  • NADPH accumulates and NADP disappears
  • without constant NADP supply, PSI and PSII are unable to operate together
  • non cylic cant occur, so cylic starts
22
Q

what happens in cyclic phosphorylation

A
  • excited e- from PSI captured by acceptors
  • returned to ground state as also pumping H+
  • so able to fall back to origin
  • proton gradient maintained and chemiosmosis conintues; ATP forms
23
Q

describe Hill’s reaction- demonstation of light dep stage outside leaf

A
  • isolate chloroplast-must be undamged and functioning- in buffer sol with conc of cytosol
  • add this to DCPIP and keep each in different intensities/wavelengths
  • isolated chlorplasts have reducing power and so liberate o2 from h2o in the presense of DCPIP the oxidixing agent which accpets e- and changes color
  • DCPIP is the lab sub for NADP
  • rate of loss of color from purple to colorless is measured by a colorimeter, and is a measure of the effect of the factor being investiagted on chloroplast acvtivity
  • time is inv prop to rate
24
Q

briefly say what happen in the light indep stage

A

in stroma co2 reduced to glucose but it depends on on ATP and NADPH from light dep stage

25
Q

describe step 1 of the Calvin cycle

A
  • co2 readily diffuses into chloroplast and combines with 5C ribulose bisphosphate under enzyme Rubisco this is fixation
  • 2 molecules of 3C glycerate 3 phosphate form (an inorganic acid)
26
Q

describe step 2 of the Calvin cycle

A
  • glycerate 3 phosphate reduced to 3C triose phosphate. this is a high energy level so bought abou t by ATP and NADPH
  • called compensation point
27
Q

describe step 3 of the Calvin cycle

A
  • RuBP regenerated 5C used
  • 1C used to form 6c glucose. cycle runs 6 times
  • some triose phosphate condense to form hexose phosphate (produces starch for storage, sucrose for translocation, cellulose for cell wall. other to glyerol+fattyacid for membrane, or acetyl coA, or amino acid production
28
Q

whats a limiting facor `

A

factor of many affecting a process whose value if lowest

29
Q

how to determine rate of photysnthesis of pondweed

A

inverted freshly cut shoot in very dilute sol of nahco3 to provide co2. stream of bubbles collected in capillary tube. calculate length trvaelled by bubblesk convert to volume then divide by unit time

30
Q

how to investigate effect of intnsity

A

-move source or one of changing power, but keep wavelength constant aka filters

31
Q

describe effect of light intnensity on photosynthesis

A
  • at constant temp it varies directly

- at higher temp the relationship doesnt hold

32
Q

whats compensation point

A

light intensity at which CO2 released in respiration=CO2 used in photosynthesis and O2 used in respiration=O2 released in photosynthesis

33
Q

co2 air conc

A

0.04%

34
Q

how does co2 effect photosynthesis

A

-as its conc increases rate increases- carbin incor-porated into carbs more fastly

35
Q

hoq to investigate co2 effect photosynthesis

A

diff nahco3 in water around plant

36
Q

how is that light indep reactions are afffected by temp but not light dep

A

enzymes may denature and hence rate of photsynthesis slows

-light dep reaction happens before indep so products on indep depends on those before

37
Q

how to investigate temp effect photosynthesis

A
  • change temp of water bath…use large one so to maintain

- boiling tubes in thermostatically controlled waterbath

38
Q

how to increase crop yield

A

-cultivation in glasshouse better than outdoor cos easy to control conditions:
>light intensity: banks of lamps of photosynthetically active radiation- wavelength chlorophyll can exploit
>heat: increase growth
>more co2: 300-1000ppm precise

39
Q

c3 vs c4 plant

A

in c3 first product in calvin cycle is 3C after 6C splits

in c4 first sugar is 4C

40
Q

whats photorespiration

A

wasteful reaction where RuBP combines with o2 and not co2 in high temp and light intesnity

41
Q

how does photrespiration happen

A

o2 from air becomes a competitive inhibitor of rubisco and hence rubisco catalyses o2+RuBP then its broken down to a 2C sugar of little value (+3C normal sugar). no RuBP left to combine with co2

42
Q

solution to c4 issue

A

Bundle sheath cells:

  • cells with rubp and rubisco arranged around vasuclar bundle withing tight ring of mesophyll which excludes air from bundle sheath
  • no direct contact with air inside leaf
  • co2 recieved from mesophyll since its in direct contact and can absorb
  • carry out calvin but not light dep
  • as o2 is a competitive inhibitor of rubisco it ensures co2 is always in high conc
43
Q

describe c4 cycle

A
  • contain enzyme PEP carboxylase: catalyses CO2+3C PEP (from light dep) to form 4C oxaloacetate
  • this converted to malate and passed onto bundle sheath cell
  • CO2 removed from malate and delivered to Rubp by rubisco to form pyruvate.
  • pyruvate goes back to mesophyll
  • bundle sheath carries out light indep reaction
44
Q

Purpose of Hill’s reaction

A

determine effect of light intensity or wavelength on rate of photosynthesis

45
Q

what are c4 plants+habitat+eg+consequence+sol

A

tropical plants- high intensity+temp
eg maize, sorghum, amaranthus
undergo photorespiration, to avoid use c4 pathway

46
Q

what is NADPH full form

A

nicotinamide adinine dinucleotide phosphate hydrogenase

47
Q

structure of NADP

A
  • 1 nucleotide of adenine, ribose, phosphate replaces the H of the OH of C2 of ribose
  • 2nd nucleotide has nicotinamide ring (has site to accept H), ribose, phosphate
48
Q

balance sheet for c3 cyle

A

RuBP, CO2, ATP, NADPH, RUBISCO : 6

Hexose sugar: 1

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