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biology module 5 > photosynthesis > Flashcards

photosynthesis Flashcards

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1
Q

what organisms are capable of photosynthesising

A

plants, algae, cyanobacteria
- these organisms are autotrophic

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2
Q

give the equation for photosynthesis

A

6CO2 + 6H2O >light> C6H12O6 + 6O2

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3
Q

define autotroph + give 1 example

A

organisms that produce food (complex organic compounds) from inorganic molecules using light energy through photosynthesis
e.g. plants

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4
Q

what type of reaction is photosynthesis

A

anabolic (building things up)

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5
Q

what is the relationship between photosynthesis and respiration

A
  • they are reverse processes
  • all organisms respire but not all photosynthesise
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6
Q

compensation point definition

A

when rates of photosynthesis and respiration are balanced

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7
Q

compensation period definition

A

time it takes to reach compensation point

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8
Q

when does photosynthesis take place

A

during the day - the intensity of light has to be sufficient to allow photosynthesis to replenish carbs used in respiration

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9
Q

when does respiration take place

A

day and night

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10
Q

how many stages are there in photosynthesis + what are they called

A

2 stages
- light dependent stage
- light independent stage aka calvin cycle

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11
Q

where does photosynthesis take place

A

in the chloroplasts

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12
Q

what 3 cell types in the leaf contain chloroplasts

A
  • palisade mesophyll
  • spongey mesophyll
  • stomatal guard cells
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13
Q

outline the general structure of a chloroplast

A
  • double membrane
  • thick fluid called stroma
  • contains an internal network of thylakoid membranes
  • these flatten into sacs called thylakoids
  • many thylakoids stacked together = granum
  • contained within the grana is the chlorophyll pigments
  • grana are linked together by thin pieces of thylakoid membrane called lamellae
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14
Q

what is the purpose of lamellae

A

ensures grana are connected but distanced

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15
Q

1 adaptation of grana

A
  • high SA:V to maximise photosynthesis
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16
Q

2 adaptations of the stroma

A
  • contains photosynthetic enzymes
  • also contains DNA and ribosomes
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17
Q

relative size of chloroplasts compared to mitochondria

A

chloroplasts are bigger

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18
Q

give the 2 main photosynthetic pigments + the colours they appear

A
  • chlorophyll a (p680)
  • chlorophyll a (p700)
    these work best at these wavelengths of light

they appear green (meaning green light is reflected, not absorbed)

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19
Q

chlorophyll a - what light is absorbed + reflected, where is it found

A
  • reflects blue green light
  • found at reaction centres of both photosystems
  • 2 forms which absorb light at wavelengths 680nm in PS2 and 700nm in PS1
  • absorbs mostly red light, only some blue (400nm)
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20
Q

give the 3 types of accessory pigments + what colours they appear

A
  • xanthopyll
  • carotenoids e.g. beta carotene
    appear yellow (meaning yellow light is reflected, not absorbed)
  • chlorophyll b
    appears yellow/green (meaning yellow/green light is reflected, not absorbed)
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21
Q

what is the function of accessory pigments

A

these pass emitted electrons to the primary pigments in photosystems

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22
Q

chlorophyll b - what light is absorbed + reflected

A
  • reflects yellow + green light
  • absorbs wavelengths 400-500nm and 640nm which is blue and red respectively
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23
Q

carotenoids - what light is absorbed + reflected

A
  • reflects yellow light
  • absorbs wavelengths 400-500nm which is blue light
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24
Q

xanthophylls - what light is absorbed + reflected

A
  • reflects yellow light
  • absorbs blue and green light between wavelengths 375-550nm
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25
Q

why do plants contain a mixture of different pigments

A

light is made up of many different wavelengths, so it allows plants to maximise light absorption for photosynthesis

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26
Q

outline the structure of a chlorophyll molecule

A
  • hydrophilic porphyrin head which lies parallel to thylakoid membrane for maximum light absorption
  • hydrophobic lipid soluble tail which lies within thylakoid membrane
  • side chains which determine which wavelengths are absorbed
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27
Q

outline a method to separate pigments

A

paper chromatography
- dissolve pigments in solvent (e.g. propanol)
- allow solvent to move up chromatography paper
- pigments will separate due to different relative adsorption
- calculate Rf values and compare to database

28
Q

where does light dependent stage take place

A

thylakoid membranes

29
Q

photosystems definition

A

contains photosynthetic pigment molecules arranged in light harvesting clusters, which are funnel shaped
- this allows each pigment molecule to pass energy down to the next within the cluster until it reaches the primary pigment reaction centre

30
Q

which type of chlorophyll is used in PS1

A

chlorophyll a p700

31
Q

which type of chlorophyll is used in PS2

A

chlorophyll a p680

32
Q

NADP definition

A

a co enzyme which can be reduced to NADPH by the addition of H+

33
Q

name 2 reaction pathways that can occur during light dependent stage

A

cyclic photophosphorylation and non-cyclic photophosphorylation

34
Q

what photosystems are involved in non-cyclic photophosphorylation

A

PS1 and PS2

35
Q

what photosystems are involved in cyclic photophosphorylation

A

PS1 only

36
Q

outline the process of non-cyclic photophosphorylation

A
  • PS2 absorbs light which excites electrons in chlorophyll to a higher energy level
  • high energy electrons are transferred to electron carrier proteins in thylakoid membranes
  • these electrons are transferred along the electron transport chain to PS1
  • as electrons move down ETC they lose energy
  • this energy is used to pump protons from the stroma into the thylakoids against their conc gradients
  • this forms a proton gradient across thylakoid membrane (higher [H+] inside than outside in stroma)
  • protons diffuse down conc gradient through ATP synthase
  • this releases energy which is used to convert ADP into ATP
  • when light energy is absorbed by PS1, high energy electrons are transferred directly to NADP (not along ETC)
  • these electrons combine with a proton in the stroma to produce NADPH
  • electrons are replaced in PS2 by the photolysis of water
37
Q

outline the process of cyclic photophosphorylation

A
  • light energy is absorbed by PS1 which excites electrons in chlorophyll to a higher energy level
  • high energy electrons are transferred to electron carrier proteins in thylakoid membranes
  • these electrons cycle through the electron transport chain continuously to PS1
  • as electrons move down ETC they lose energy
  • this energy is used to pump protons from the stroma into the thylakoids against their conc gradients
  • this forms a proton gradient across thylakoid membrane (higher [H+] inside than outside in stroma)
  • protons diffuse down conc gradient through ATP synthase
  • this releases energy which is used to convert ADP into ATP
38
Q

1 similarity and 3 differences between cyclic (C) and non-cyclic (NC) photophosphorylation

A
  • ATP is produced in both C and NC
  • NADPH is produced in NC but not in C
  • in C electrons are continuously recycled but in NC they need to be replaced
  • NC involves the photolysis of water, whereas C doesn’t
39
Q

chemiosmosis definition

A

the process by which the movement of protons/H+ down their concentration gradient releases energy which is then used for ATP synthesis

40
Q

outline the role of chlorophyll in photolysis of water

A

lost electrons from photolysis that go to the chlorophyll after absorbing light
this causes more water to dissociate

41
Q

give the equation for the photolysis of water

A

H2O&raquo_space; 1/2O2 + 2H+ + e-

42
Q

where does oxygen from the photolysis of water go

A
  • released through stomata
  • used in respiration
43
Q

what are the products of light dependent stage

A
  • NADPH
  • ATP
44
Q

where does the calvin cycle take place

A

stroma

45
Q

what are the 3 stages of the calvin cycle

A

1 carbon fixation
2 reduction
3 regeneration

46
Q

fixation definition

A

the process by which a small molecule is incorporated into an organic molecule

47
Q

outline the process of the calvin cycle

A

1 CARBON FIXATION
- 5C molecule RuBP is combined with CO2 in a reaction catalysed by enzyme RuBisCO
- this forms an unstable 6C intermediate which immediately breaks down into 2 3C GP molecules
2 REDUCTION
- each GP molecule reduced once using NADPH»NADP+ using energy from ATP»ADP
- this forms 2 3C TP molecules
3 REGENERATION
- 1/6th of the 2 TP molecules formed is taken out of the cycle and further metabolised
- the other 5/6ths are phosphorylated again using ATP»ADP to reform RuBP

48
Q

what are 2 limitations of RuBisCO

A
  • not very efficient so plants need to have a lot of it (makes up around 50% of protein in chloroplasts)
  • not very specific meaning it can combine with O2 instead of CO2, creating a useless intermediate - this means the calvin cycle cannot happen in high [O2]
49
Q

how many turns of the calvin cycle are needed to produce 1 glucose molecule

A

6 turns

50
Q

of the 12 TP molecules produced in 6 turns of the calvin cycle, how many are removed to make glucose + what happens to the rest

A

1/6th = 2 TP molecules are removed
5/6ths = 10 TP reform RuBP

51
Q

what can TP be metabolised into

A
  • glucose + RuBP mainly
  • from here it can be synthesised into sucrose, starch, cellulose
  • it can also be a starting material for fatty acids, glycerol, amino acids
52
Q

when does the calvin cycle occur

A

it only happens during the day, as it still relies on a continuous supply of NADPH and ATP from light dependent stage

53
Q

where does the CO2 needed for calvin cycle come from

A
  • respiration
  • other organisms + the air, entes plant through the stomata
54
Q

give 4 factors affecting photosynthesis

A
  • light intensity
  • CO2 concentration
  • temperature
  • water stress (not a main one)
55
Q

how does light intensity affect photosynthesis

A

greater light intensity = greater rate of photosynthesis

  • light provides energy to produce ATP and NADPH in light dependent stage
  • allows stomata to open, enabling gas exchange
  • transpiration occurs, allowing water from roots to travel + be evaporated
56
Q

how does light intensity affect concentrations of RuBP TP and GP

A

decreased light intensity causes TP + RuBP conc to decrease, and GP to increase slightly

less light = decreased rate of light dependent stage = less ATP and NADPH made meaning GP builds up as it cannot be converted into TP, and so there is less TP and less RuBP formation

57
Q

how does CO2 concentration affect the rate of photosynthesis

A

greater CO2 concentration = greater rate of photosynthesis

  • CO2 levels in the atmosphere and aquatic habitats are usually high enough to not become a limiting factor
58
Q

how does CO2 concentration affect concentrations of RuBP TP and GP

A

decreased CO2 concentration causes GP + TP conc to decrease and RuBP conc to increase

less CO2 = less carbon fixation causing RuBP to build up as it cannot be converted into GP, so less GP so less TP

59
Q

how does temperature affect photosynthesis

A

generally as temperature increases, rate of photosynthesis increases, however if it continues to increase past optimum temps rate of photosynthesis decreases

25-30C - rate increases as enzymes have more energy so move faster
30-45C - O2 more successfully competes with CO2 for active site of RuBisCO causing rate to decrease
45C+ - enzymes denature causing rate to decrease

60
Q

how does temperature affect concentrations of RuBP TP and GP

A

as temp increases, rate of calvin cycle increases as it is an enzyme controlled reaction

too high temps = O2 filling binding sites or enzymes becoming denatured = no carbon fixation so GP cannot be formed, so less GP so less TP, RuBP initially builds up slightly but it cannot be regenerated

61
Q

outline an experiment to measure the impact of an abiotic factor on the rate of photosynthesis

A

1 - make leaf extract
- grind up leaves with a pestle and mortar in isolation medium
- filter then cool and centrifuge filtrate to get a pellet of chloroplasts
- transfer pellets to boiling tubes with isolation medium and use a pipette to squirt the mixture in and out several times to get a uniform suspension

2 - DCPIP
- set up several tubes with the same volume of leaf extract and different environments - e.g. water baths, around a lamp
- add a few drops of DCPIP to each test tube and set up in different environments - e.g. differing distances from the lamp + in the dark, in different temps in water/ice baths
- record how long it takes for DCPIP in each tube to decolourise
- use this to measure rate of decolourisation = rate of photosynthesis
- set up some controls to increase validity

62
Q

how does the DCPIP experiment work

A

DCPIP is an electron acceptor, so can accept electrons released from photolysis of water during LDS causing it to be reduced and turn colourless
faster rate of LDS = faster rate of photosynthesis = faster decolourisation of DCPIP

63
Q

what will occur when DCPIP is reduced

A

a colour change from dark blue to colourless

64
Q

what is the purpose of a control

A

to validate results by proving that the change being observed is not being caused by other factors

65
Q

describe 3 control experiments that could be used when investigating the rate of photosynthesis with DCPIP

A

1 - wrapping a test tube in aluminium foil
this shows that the colour change only occurs when there is light present

2 - replacing chloroplast suspension with buffer solution
this shows that chloroplasts are required for the colour change

3 - leaving DCPIP out of a test tube
this shows that the DCPIP is causing the colour change

66
Q

which experimental technique could be used to separate various photosynthetic pigments

A

chromatography

biology module 5 (7 decks)

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