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Biology IB HL > C1.3 Photosynthesis > Flashcards

C1.3 Photosynthesis Flashcards

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1
Q

What is photosynthesis?

A
  • the conversion of light energy to chemical energy -> pigments (coloured substances e.g chlorophyll)
  • Carbon compounds produced contain chemical energy previously light. (glucose)
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2
Q

Equation for photosynthesis?

A

Carbon dioxide + water (+light) -> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2

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3
Q

What are light dependent reactions?

A

reactions that require light in order to occur.
occur on the thylakoid membranes
- photolysis of water
- photophosphorylation

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4
Q

What are light independent reactions?

A

reactions that do not req light, occur in stroma
- e.g carboxylation (carbon fixation)
- calvin cycle
- synthesis of carbohydrates

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5
Q

How is hydrogen and oxygen obtained?

A
  • splitting water molecules into hydrogen and oxygen (byproduct)-> when light is available -> energy req
  • twelve molecules split for 1 glucose molecule
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6
Q

organisms carrying out photosynthesis?

A
  • plants
  • algae
  • cyanobacteria

bubbles underwater produced (o2) rise to surface
terrestrial organisms diffuse o2 to atmosphere

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7
Q

Outline an experiment for chromatography

A

1) tear leaf to small pieces
2) grind leaf -> with sharp sand + propanone -> extract pigments
3) sample -> watch glass
4) evaporate to dryness -> hot air (blow dryer)
5) drops of propanone -> dissolve pigments
6) place a concentrated amount 10mm away from end of chroma paper
7) suspend strip -> tube -> base dips into solvent
8) remove -> when solvent nearly reached top -> pencil line, shows how far solvent moved (draw)
9) pigment identified by:
- colour
- Rf value

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8
Q

what does the rf value show?

A
  • pigments travel -> different rates -> whether pigment is more attracted to the hydrophobic solvent -> or hydrophilic chromatography strip
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9
Q

rf value

A

Distance moved by spot/distance moved by solvent

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10
Q

general rule between wavelength and energy?

A
  • shorter WL, higher energy a photon of light has
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11
Q

What happens when a photosynthetic pigment uses energy obtained from absorption of light?

A
  • electron in molecule -> higher energy level jump
  • conversion of energies
  • “excited” electron -> can be passed on to other molecules
  • energy carried by electrons -> ends up in glucose/other compounds
  • specific wavelengths required -> have the amount of energy needed -> other wavelengths are reflected
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12
Q

What wavelengths does chlorophyll absorb effectively?

A
  • red, blue
  • green is mostly reflected, making it appear green
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13
Q

other pigments used in photosynthesis?

A

-xanthophyll, carotene

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14
Q

What is an absorption spectra?

A
  • graph -> shows the absorbance of light by photosynthetic pigments (here chlorophyll) for all the wavelengths of light
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15
Q

action spectra

A

Action spectrum is a graph curve depicting the relative rates of photosynthesis for all wavelengths of light as a % maximum rate

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16
Q

What is a limiting factor?

A
  • factor limiting rate at a particular time -> nearest to its minimum
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17
Q

temperature as a limiting factor

A

increases -> rate increases steeply until optimum temp -> past, and rate falls steeply

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18
Q

light intensity as a limiting factor

A

at low/medium, rate is directly proportional to intensity
at high, intensities -> rate plateaus

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19
Q

co2 concentration as a limiting factor

A

no photosynthesis -> low conc
low - high -> positive correlated (conc and rate)
very high -> plateaus

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20
Q

Design an investigation to deduce rate of photosynthesis…

A
  • 1 limitant investigated (IV)
  • suitable range should be chosen (lowest to where no longer limits)
  • accurate method chosen for rate (DV) -> measure of o2 production per unit time
  • all other factors are constant (CV)
21
Q

How to measure temperature

A
  • place pondweed -> thermostatically controlled water bath
  • 5 - 45C (in 5/10 intervals)
  • Controlling factor: set thermo at 25 and keep it there throughout experiment
22
Q

How to measure light intensity

A
  • move light source -> different distances -> measure intensity -> lux metre -> intensity = 1/distance^2
  • range: 4,5,7,10,14 cm, + no light
  • Controlling factor: keep light source at constant distance (5cm)
23
Q

How to measure co2

A
  • use pondweed, place in beaker
  • start with boiling, cooled water -> add NaHCO3 -> increase co2 concentration
  • range = 0-50 mmol dm^-3 -> in 10 mmol dm^-3 intervals
  • Controlling: add enough -> give high concentration (50 mmol dm^-3)
24
Q

What are carbon dioxide enrichment experiments?

A
  • experiments to predict future rates of photosynthesis and plant growth
  • co2 artificially increased - e.g greenhouses + free air carbon dioxide enrichment (FACE) experiments.
25
Q

what are the FACE experiments (Free air carbon dioxide enrichment)

A
  • circles of towers built -> co2 released
  • co2 concentration monitored -> inside circles -> released upwind
  • control plots are used -> air instead
  • thus rise can predict consequences for plants + other stakeholders
  • hypothesis that increased photosynthesis + plant growth -> moderate rises in co2 conc can be tested
26
Q

What are photosystems?

A
  • molecular arrays -> chlorophyll accessory pigments
  • special chlorophylls in reaction centre -> pairs of excited electrons emitted
  • in thylakoid membrane
27
Q

What is a thylakoid?

A
  • sac like vesicle
  • flattened and arranged in stacks in chloroplasts for photosynthetic eukaryotes
28
Q

Two types of photosystems

A

PS1:
- positioned -> thylakoid membrane exposed to stroma surrounding
PS2:
- not in contact with stroma

29
Q

Functional units of Photosystems?

A
  • reaction centre -> special chlorophyll -> emits e*
  • antenna complexes -> harvest light energy -> funnel to reaction centre -> many pigment molecules -> precise arrangement
30
Q

Advantages of a structured array of different types of pigment molecules in a photosystem?

A
  • wider array -> larger no. pigment -> intercept more photons > supplies energy to reaction centre -> faster rate
  • Wider range of wavelengths absorbed-> due to many different types of pigment
  • energy transferred pigment to pigment -> excitation energy transfer (photoactivation) -> precise array in antenna complex - energy funnelled to reaction centre
31
Q

What occurs during photolysis of water in PS II

A
  • P680 (chlorophyll) in centre emits e* -> reduced P680 -> until it regains an e
  • it is released after photolysis -> in OEC facing the space inside thylakoid
  • OEC binds two water molecules and splits them -> 4e 4p and 1 o2
  • electrons passed to -> p680
  • protons released -> thylakoid space -> proton gradient across membrane
  • o2 waste, diffuses out
32
Q

What has the advent of oxygen generation by photolysis done for living organisms and geological processes?

A
  • it initiated accumulation of o2 in atmosphere -> organisms respire aerobically -> oxidation of dissolved iron+other minerals in oceans occur
33
Q

What is chemiosmosis?

A
  • Production of ATP -> potential energy from the proton gradient from chains of electron carriers -> in thylakoid
  • excited electrons pass ETC, releases energy -> pump protons, stroma to thylakoid space
34
Q

How can electrons be supplied?

A

Cyclic Photophosphorylation
- process of producing ATP from ADP with light.
- pairs of excited electrons -> emitted (PSI) -> after passing ETC -> return

Non cyclic Photophosphorylation
- Pairs of excited (PSII) -> flow to PSI

35
Q

What is Reduced NADP?

A
  • useful product of LDR in thylakoids
  • ferredoxin accepts electrons emitted from PSI
  • binds to NADP reductase -> transfers electron it is carrying
    -> reducing it

NADP + 2e- -> NADPH

36
Q

how does NADP collide with ferredoxin?

A
  • NADP is dissolved in stroma -> reduced -> molecular motion brings it to the enzyme’s active site.
  • electrons emitted by PSI replaced by PSII -> passed to ETC
  • Production of NADPH is accompanied by non-cyclic Photophosphorylation
37
Q

What are thylakoids?

A

systems that consist of interacting and interdependent components

38
Q

why is the thylakoid membrane a key component?

A

impermeable to protons -> gradient develops
encloses small vol of fluid - gradient develops rapidly
phospholipids, hold photosystems -> made of hydrophobic pigments
hold other components in correct relative positions (e.g above carriers, reductase, synthase)

39
Q

What are thylakoid components dependent on?

A
  • PS II supplying e*
  • Electron carrier chain supplies energy
  • proton pumps -> create -> gradient -> used by ATP synthase
  • PS I supplies excited electrons to NADP reductase
  • PS II resupplies PS I with electrons
  • Water in thylakoid space -> supplies electrons to PS II
40
Q

What is rubisco?

A
  • enzyme responsible for catalysing the addition of carbon dioxide to Ribulose Biphosphate
  • most abundant enzyme on Earth
41
Q

What is carbon fixation?- light independent reaction

A
  • the production of organic compounds from co2
42
Q

Where does co2 come from?

A
  • diffuses into stroma of chloroplast -> converted to more complex carbon compound, RuBP, is found in the stroma and reacts.
43
Q

What happens within the carboxylation (COOH addition) reaction catalysed by rubisco?

A
  • co2 combines -> ribulose bisphosphate (RuBP), pentose -> product, unstable six carbon compound -> splits to glycerate 3 phosphate

RuBP + CO2 -> 2 Glycerate-3-Phosphate (organic acid)

44
Q

Limitations of Rubisco?

A
  • high concentrations needed in stroma
  • works slowly
  • not effective in low co2 conc
45
Q

How is triose phosphate formed?

A
  • Glycerate 3 phosphate -> triose phosphate (3 carbon) by reduction in stroma
    hydrogen needed -> from NADPH
  • energy supplied by ATP

Glycerate 3 phosphate + Reduce NADP + ATP -> TP + NADP + ADP

46
Q

What is the Calvin cycle? (all carbon in compounds is fixed in calvin cycle, except glucose are traced back to an intermediate used)

A
  • series of biochemical reactions to convert co2 to glucose
    stages brief:
    1) Co2 and RuBP, rubisco -> produce glycerate 3 phosphate (carbon fixation)
    2) reduction, ATP and NADPH produced from LDR convert intermediate to triose phosphate (glyceraldehyde-3-phosphate)
    3) some TP molecules -> regenerate RuBP -> cycle continues -> remaining converted to compounds -> source of energy + building blocks
47
Q

What is required for the Calvin cycle to continue?

A
  • regeneration of RuBP, 5/6 molecules of TP from light independent reaction used. 1 exits cycle
48
Q

How is glucose produced?

A
  • linking of two TP
  • can be converted to other carbs e.g sucrose/starch
  • pathways for aminos and fatty acids start with glycerate or TP or any intermediate from aerobic
49
Q

Why are photosynthesis reactions interdependent?

A
  • light independent reactions cannot happen without…
    ATP, and NADPH from light dependent reactions.
    Light dependent reactions require ADP and NADP -> independent reactions produce

Biology IB HL (14 decks)

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