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OCR A level Biology HJ > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

why is energy important?

A
  • living things need energy for biological processes to occur
  • without energy, these biological processes would stop and the plant, animal and microorganism would die
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2
Q

why do plants need energy?

A

-for things like photosynthesis, active transport (e.g. to take in minerals via their roots), DNA replication and cell division

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3
Q

why do animals need energy?

A

-for things like muscle contraction, maintenance of body temperature, active transport, DNA replication and cell division

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4
Q

why do microorganisms need energy?

A

-for things like DNA replication, cell division, protein synthesis and sometimes motility (movement)

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5
Q

how do plants make their own food?

A

using photosynthesis (they make glucose)

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6
Q

what is photosynthesis?

A

photosynthesis is the process where energy form light is used to make glucose from water (H2O) and carbon dioxide (CO2).

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7
Q

how is light energy converted to chemical energy?

A

in the form of glucose

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8
Q

what is the formula for glucose?

A

C6H12O6

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9
Q

what is the overall equation for photosynthesis?

A

6CO2 + 6H2O + Energy —-> C6H12O6 + 6O2

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10
Q

how is energy stored in the glucose released?

A

by respiration

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11
Q

as animals can’t make their own food, how do they obtain glucose?

A

-by eating plants (or other animals), then respire the glucose to release energy

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12
Q

what is the process of respiration?

A

when living cells release energy from glucose

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13
Q

what are the 2 types of respiration and what is the difference?

A
  • aerobic respiration - respiration using oxygen

- anaerobic respiration - respiration without oxygen

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14
Q

what is the overall equation for aerobic respiration?

A

C6H12O6 + 6O2 —-> 6CO2 + 6H2O + Energy

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15
Q

what is the immediate source of energy in a cell?

A

ATP (adenosine triphosphate

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16
Q

how does a cell get its energy directly from glucose?

A

a cell can’t get its energy directly from glucose

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17
Q

how is ATP made and what does it do?

A
  • in respiration, the energy released from glucose is used to make ATP
  • it carries energy around the cell to where it’s needed
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18
Q

what is ATP made of?

A
  • the ATP is made from the nucleotide base adenine, combined with a ribose sugar and the 3 phosphate groups
  • ATP is synthesised from ADP and Pi (inorganic phosphate using energy from an energy- releasing reaction, e.g. the breakdown of glucose in respiration
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19
Q

how is the energy in ATP stored?

A

the energy is stored as chemical energy in the phosphate bond

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20
Q

what is the enzyme that catalyses the reaction between ADP + Pi?

A

ATP synthase

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21
Q

what is the process of phosphorylation?

A

adding phosphate to a molecule

-ADP is phosphorylated to ATP

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22
Q

how does ATP get to the part of the cell that needs energy and what happens?

A
  • ATP then diffuses to the part of the cell that needs energy
  • here, it’s broken down into ADP and inorganic phosphate (Pi)
  • chemical energy is released from the phosphate bond and used by the cell
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23
Q

what enzyme catalyses the reaction for the breakdown of ATP and water to make ADP and Pi?

A

ATPase

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24
Q

what is the process of ATP and water to make ADP and Pi called?

A

hydrolysis (the splitting of a molecule using water

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25
Q

what are the 5 properties of ATP that make it a good source of energy?

A
  • ATP stores or releases only a small, manageable amount of energy, so no energy is wasted
  • it’s a small, soluble molecule so it can be easily transported around the cell
  • it’s easily broken down, so energy can be easily released
  • it can transfer energy to another molecule by transferring one of its phosphate groups
  • ATP can’t pass out of the cell, so the cell always has an immediate supply of energy
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26
Q

what factors does the rate at which photosynthesis takes place partly depend on?

A

-the light intensity of the environment that the plant is in

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27
Q

as plants carry out photosynthesis and respiration at the same time, is the rate the same?

A

both processes can occur at the same time and at different rates

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28
Q

what does the compensation point of light intensity mean?

A

the particular level of light intensity at which the rate of photosynthesis exactly matches the rate of respiration

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29
Q

how do you work out the compensation point for a plant?

A

-measure the rate at which oxygen is produced and used by a plant at different light intensities

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30
Q

why is the method that we use to work out the compensation point acceptable?

A

-because photosynthesis produces oxygen and respiration uses it, in this case, the compensation point is the light intensity at which oxygen is being used as quickly as it produced

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31
Q

where in the plant cell does photosynthesis occur?

A

photosynthesis takes place in the chloroplasts of plant cells

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32
Q

describe the structure of the chloroplast

A
  • chloroplasts are small, flattened organelles found in plant cells.
  • they have a double membrane called the chloroplast membrane.
  • thylakoids (fluid-filled sacs) are stacked up in the chloroplast into structures called grana (singular= granum)
  • the grana are linked together by bits of thylakoid membrane called lamellae (singular= lamella)
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33
Q

what are the photosynthetic pigments that chloroplasts contain?

A

-chlorophyll b and carotene

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34
Q

what is the role of chlorophyll b and carotene?

A

the are coloured substances that absorbs that absorb the light energy needed for photosynthesis

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35
Q

where are the chlorophyll b and carotene pigments found?

A

thylakoid membranes- they’re attached to proteins

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36
Q

what is the protein and pigments in the chloroplast called?

A

a photosystem

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37
Q

what are the 2 types of photosynthetic pigments called?

A
  • primary pigments

- accessory pigments

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38
Q

what are primary pigments?

A

primary pigments are reaction centres where electrons are excited during the light- dependent reaction

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39
Q

what is the primary pigment in most chloroplast?

A

chlorophyll a

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40
Q

what do accessory pigments make up?

A

light-harvesting systems

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41
Q

what is the role of accessory pigments?

A

These surround reaction centres and transfer light energy to them to boost the energy available for electron excitement to take place.

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42
Q

how many photosystems are there?

A

2

  • photosystem I
  • photosystem II
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43
Q

what is the role of photosystems?

A

-they are used by plants to capture light energy

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44
Q

what wavelengths do PSI and PSII best absorb light?

A
  • PSI= 700nm

- PSII= 680nm

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45
Q

what is the stroma and where is it found?

A

contained within the inner membrane of the chloroplast and surrounding the thylakoids
-its a gel-like substance

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46
Q

what does the stroma contain?

A

-it contains enzymes, sugars and organic acids

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47
Q

where is the DNA in the chloroplast found?

A
  • chloroplasts have their own DNA
  • it’s found in the stroma and is often circular
  • there can be multiple copies in each chlorplast
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48
Q

what happens to carbohydrates produced by photosynthesis?

A

carbohydrates produced by photosynthesis and not used straight away are stored as starch grains in the stroma

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49
Q

what does it mean for something to be reduced?

A
  • gained electrons (e-)
  • gained a hydrogen
  • lost oxygen
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50
Q

what does it mean for something to be oxidised?

A
  • lost electron
  • lost hydrogen
  • gained oxygen
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51
Q

what is a coenzyme + how do they work?

A
  • a coenzyme is a molecule that aids the function of an enzyme
  • they usually work by transferring a chemical from one molecule to another
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52
Q

what is the coenzyme that is used in photosynthesis?

A

NADP

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53
Q

what is the role of NADP?

A

NADP transfers hydrogen from one molecule to another- this means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule

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54
Q

what are the 2 stages of photosynthesis?

A

1) the light-dependent reaction

2) the light-independent reaction (the Calvin cycle)

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55
Q

where does the light-dependent reaction take place?

A

the thylakoid membranes of the chloroplast

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56
Q

what happens in the thylakoid membranes during the light-dependent reaction?

A
  • light energy is absorbed by photosynthetic pigments in the photosystems and converted to chemical energy
  • the light energy is used to add a phosphate group to ADP to form ATP, and to reduce NADP to form reduced NADP
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57
Q

what is reduced NADP?

A

reduced NADP is an energy-rich molecule because it can transfer hydrogen, and so electrons, to other molecules

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58
Q

what is the difference between the roles of ATP and reduced NADP during the light-independent?

A

ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction

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59
Q

what happens to water (H2O) during the light-dependent reaction?

A

during this process water (H2O) is oxidised to oxygen (O2)

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60
Q

what is the difference between the light-dependent and light-independent reaction?

A 
light-dependent= this reaction needs light energy
light-independent= this reaction doesn't use light energy directly
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61
Q

how does the light-independent reaction indirectly need energy?

A

it relies on the products of the light-dependent reaction

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62
Q

where does the light independent reaction take place?

A

it takes place in the stroma of the chlorplast

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63
Q

what happens in the light-independent reaction?

A

-the ATP and reduced NADP from the light-dependent reaction supply the energy and hydrogen to make glucose form CO2

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64
Q

how long does the light-independent reaction take place after it gets dark?

A
  • the light-independent reaction can take place in the dark
  • however, it needs the products of the light-dependent reaction (ATP and reduced NADP)

=so in reality it only continues for a light while after it gets dark

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65
Q

draw a diagram of how the light -dependent and light-independent reaction link together in the chloroplast

A

insert pic page 394 CGP

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66
Q

draw a diagram of the chloroplast?

A

insert pic page 395 CGP

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67
Q

what 3 processes is the light energy absorbed by the photosystems during the light-dependent reaction used for?

A

1- making ATP from ADP and inorganic phosphate. This is called photophosphorylation- it’s he process of adding phosphate to a molecule using light.

2- making reduced NADP from NADP

3- splitting water into protons (H+), electrons and oxygen. This is called photolysis- it’s the splitting (lysis) of a molecule using light (photo) energy.

68
Q

what are the 2 types of phosphorylation that occur during the light-dependent reaction?

A

non-cyclic and cyclic

69
Q

what are the products of non-cyclic phosphorylation?

A

-ATP, reduced NADP and oxygen (O2)

70
Q

what links the photosystems in the thylakoid membranes?

A

photosystems in the thylakoid membranes are linked by electron carriers

71
Q

what are electron carriers?

A

electron carriers are proteins that transfer electron

72
Q

what do the photosystems and electron carriers form?

A

-they form an electron transport chain- a chain of proteins through which excited electron flow

73
Q

what are the 4 processes that occur during non-cyclic photophosphorylation?

A

1- light energy excites electrons in chlorophyll
2- photolysis of water produces protons, electrons and oxygen
3- energy from the excited electrons makes ATP
4- energy from the excited electrons generates reduced NADP

74
Q

what occurs during the process in which light energy excites electrons in chlorophyll?

A
  • light energy is absorbed by PSII
  • the light energy excites electrons
  • the electrons move to a higher energy level (i.e they have more energy)
  • these high-energy electrons move along the electron transport chain
75
Q

what occurs during the process in which photolysis of water produces protons, electrons and oxygen?

A
  • as the excited electrons from chlorophyll leave PSII to move along the electron transport chain, they must be replaced
  • light energy splits water into protons (H+ ions), electrons and oxygen (so the oxygen in photosynthesis comes from water)

The reaction is: H20 —-> 2H+ + 1/2O2

76
Q

what occurs during the process in which energy form the excited electrons makes ATP?

A
  • the excited electrons lose energy as they move along the electron transport chain.
  • this energy is used to transport protons (H+ ions) into the thylakoid membrane proteins called proton pumps, so that the thylakoid has a higher concentration of proton than the stroma
  • this forms a proton gradient across the membrane
  • protons move down their concentration gradient, into the stroma, via an enzyme called ATP synthase
  • the energy from this movement combines ADP and inorganic phosphate (Pi) to form ATP
77
Q

what occurs during the process in which energy from the excited electrons generates reduced NADP?

A
  • light energy is absorbed by PSI, which excites the electrons again to even high energy level
  • finally, the electrons are transferred to NADP, along with a proton form the stroma, to form reduced NADP
78
Q

draw a flow diagram to show how reduced NADP is formed during non-cyclic phoyophosphorylation

A

insert a pic page 396 and 397 CGP

79
Q

how is ATP formed in both cyclic and non-cyclic phosphyraltion?

A

by the movement of protons across the thylakoid membrane

80
Q

what are the products of cyclic phosphorylation?

A

cyclic photophosphorylation only produces ATP and only uses PSI

81
Q

why is cyclic phosphorylation ‘cyclic?

A
  • it’s called ‘cyclic’ because the electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers
  • this process doesn’t produce any reduced NADP or oxygen- it only produces small amounts of ATP
82
Q

draw a diagram for cyclic phosphorylation

A

insert pic page 397 CGP

83
Q

why is the O2 produced from photolysis of water important?

A

it diffuses out of the chloroplast and eventually into the atmosphere for us to breathe

84
Q

what is chlorophyll fluorescence?

A

-if too much light energy has been absorbed, plants release some of the excess energy by emitting fluorescent light

85
Q

what’s chemiosmosis?

A

The movement of protons (H+) as they flow from a region of high concentration to a region of low concentration through a partially permeable membrane.
This releases energy that is used to attach Pi to ADP forming ATP

86
Q

what is another name for the light-independent reaction?

A

the Calvin cycle

87
Q

where does the Calvin cycle take place?

A

it takes place in the stroma of the chloroplast

88
Q

what happens in the Calvin cycle?

A

-it makes a molecule called triose phosphate from carbon dioxide (CO2) and ribulose bisphosphate ( a 5-carbon compound)

89
Q

what is the use of triose phosphate?

A

triose phosphate can be used to make glucose and other useful organic substances

90
Q

what is needed to keep the Calvin cycle going?

A
  • ATP

- H+ ions

91
Q

what does it mean for ribulose bisphosphate being the starting compound mean?

A

it is regenerated

92
Q

draw one turn of the Calvin cycle

A

insert pic page 399 CGP

93
Q

what are the 3 stages of the Calvin cycle?

A

1- formation of glycerate 3-phosphate
FIXATION= CO2 is fixed (incorporated into an organic molecule)
2-formation triose phosphate
REDUCTION= GP is reduced to TP by the addition of hydrogen from reduced NADP using energy supplied by ATP
3-regeneration of ribulose bisphosphate
REGENERATION= RuBP is regenerated from the recycled TP

94
Q

what happens in the 1st stage of the Calvin cycle (where 3-glycerate 3- phosphate is formed)?

A

1- CO2 enters the leaf through the stomata + diffuses into the stroma of the chloroplast

2- here it’s combined with ribulose bisphosphate (RuBP), 5 carbon compound

3- this gives an unstable 6- carbon compound, which quickly breaks down into 2 molecules of a 3-carbon compound called glycerate 3-phosphate (GP).

95
Q

what is the name of the enzyme that catalyses the reaction between CO2 and RuBP?

A

ribulose bisphosphate carboxylase

96
Q

what is the equation for the formation of glycerate 3-phosphate?

A

RuBP (5C)+CO2 ————>unstable 6C compound —–> 2*GP (3C)
RuBisCO

97
Q

why is the carbon cycle also called carbon dioxide fixation?

A

because carbon dioxide is ‘fixed’ into an organic molecule

98
Q

what happens in the 2nd stage of the Calvin cycle ( where triose phosphate is formed)?

A

1- the 3- carbon compound GP (glycerate 3-phosphate) is reduced to a different 3- carbon compound called triose phosphate (TP)

2- ATP (form the light- dependent reaction reaction) provides the energy to do this

3-This reaction also requires H+ ions, which come from reduced NADP (also from the light-dependent reaction)

4-reduced NADP is recycled to NADP (for use in the light-dependent (for use in the light-dependent reaction again)

5-Triose phosphate is then converted into many useful organic compounds, e.g. glucose

99
Q

what’s the equation for the second stage in the Calvin cycle (formation of triose phosphate)?

A

insert pic bottom of page 399 CGP

100
Q

what happens in the 3rd stage of the Calvin cycle (regeneration of ribulose bisphosphate)?

A

1- 5/6 molecules of TP produced in the cycle aren’t used to make useful organic compounds, but to regenerate RuBP

2- regenerating RuBP uses the rest of the ATP produced by the light- dependent reaction

101
Q

what’s the equation for the 3rd stage of the Calvin cycle (regeneration of ribulose bisphosphate)?

A

insert pic top of page 400 CGP

102
Q

what is a hexose sugar?

A

-a hexose sugar is a monosaccharide that has six carbon atoms, e.g. glucose

103
Q

how are hexose sugars made?

A

-one hexose sugar is made by joining two molecules of triose phosphate (TP) together

104
Q

what are hexose sugars used for?

A

hexose sugars can be used to make larger carbohydrates

105
Q

how many times does the Calvin cycle need to turn to make 1 hexose sugar and why?

A
  • 6 times
  • the reason for this is that 3 turns of the cycle produces six molecules of triose phosphate (because 2 molecules of TP molecules are made for every one CO2 molecule used)
106
Q

how many of he triose phosphate molecules produced are used to regenerate RuBP?

A

5/6 meaning that for three turns of the cycle only one TP is produced that’s used to make a hexose sugar

107
Q

how many ATP and reduced NADP is needed from the light-dependent reaction in 6 turns of the Calvin cycle?

A

18 ATP

12 reduced NADP

108
Q

draw a diagram of 6 turns of the Calvin cycle

A

insert pic bottom of page 400 CGP

109
Q

what are triose phosphate and glycerate 3-phosphate used to make?

A
  • CARBOHYDRATES= hexose sugars are made from two triose phosphate molecules and larger carbohydrates (e.g. sucrose, starch, cellulose) are made by joining hexose sugars together in different ways.
  • LIPIDS= these are made using glycerol, which is synthesised from triose phosphate, and fatty acids, which are synthesised from glycerate 3-phosphate
  • AMINO ACIDS= some amino acids are made from glycerate 3-phosphate
110
Q

what are the inputs and outputs of the Calvin cycle?

A 
Inputs:
-CO2
-ATP
-reduced NADP
 |
 |
 |
\/
Outputs:
-Organic substances
-RuBP
111
Q

what are some factors that can act as limiting factors for photosynthesis?

A
  • light
  • temperature
  • carbon dioxide
112
Q

what are some conditions that would lead to optimum conditions for photosynthesis?

A

1- high light intensity of a certain wavelength
2- temperature around 25 degrees
3- carbon dioxide at 0.4%

113
Q

why would high light intensity of a certain wavelength be an optimum condition for photosynthesis?

A
  • light is needed to provide the energy for the light-dependent reaction- the higher the intensity of the light, the more energy it provides
  • only certain wavelengths of light are used for photosynthesis
  • the photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorbs the red and blue light in sunlight
114
Q

why is a temp of around 25 degrees the optimum temperature for photosynthesis?

A

because the enzymes (ATP synthase, RuBisCO) work best at this temp

115
Q

what happens to the rate of photosynthesis when the temp falls below 10 degrees?

A

the enzymes become inactive

116
Q

what happens to the rate of photosynthesis if the temp rises above 45 degrees?

A

they start to denature ( lose structure and function)
ALSO:

  • stomata close to avoid losing too much water. This causes photosynthesis to slow down because less CO2 enters the leaf when the stomata are closed
  • the thylakoid membranes may be damaged. This could reduce the rate of the light-dependent stage reactions by reducing the number of sites available for electron transfer
  • the membrane around the chloroplast could be damaged, which could cause enzymes important in the Calvin cycle to be released into the cell. This would reduce the rate of the light-independent stage reactions
  • Chlorophyll could be damaged. this would reduce the amount of pigment that can absorb light energy, which would reduce rate of the light-dependent stage reactions.
117
Q

why is a CO2 level of 0.4% optimum?

A

increasing the level to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close

118
Q

on a sunny, warm windless day, what’s the limiting factor of photosynthesis?

A

level of CO2

119
Q

at night, what’s usually the limiting factor of photosynthesis?

A

light intensisty

120
Q

draw and annotate a graph showing how light intensity can be the limiting factor of photosynthesis

A

-inert pic page 403 CGP

-light intensity increases so does photosynthesis
the graph plateaus at point B which is the saturation point = increasing light intensity after this point makes no difference because there’s something else which has become the limiting factor

121
Q

draw and annotate a graph showing how temperature can be the limiting factor of photosynthesis

A
  • insert pic page 403 CGP
  • the graph at 25 degrees levels off at a higher point than at 15 degrees. showing that at 15 degrees, the temperature must have been a limiting factor
122
Q

draw and annotate a graph showing how carbon dioxide can be the limiting factor of photosynthesis

A
  • insert pic page 404 CGP
  • the graph at 0.4% carbon dioxide (CO2) levels off at a higher point than the one at 0.04%, so CO2 concentration must have been a limiting factor at 0.04 CO2. The limiting factor here isn’t temperature because it’s the same for both graphs (25 degrees)
123
Q

how can water stress effect the rate of photosynthesis?

A

-when plants don’t have enough water, their stomata will close to preserve what little water they do have, leading to less CO2 entering the leaf for the Calvin cycle and slowing photosynthesis

124
Q

how and why do farmers create optimum conditions for photosynthesis?`

A
  • they use glasshouses

- which increases, growth and yield therefore profit

125
Q

what are the limiting factors of photosynthesis and how do commercial growers (farmers) manage these conditions in glasshouses?

A
  • carbon dioxide=
  • CO2 is added to the air, e.g by burning a small amount of propane in a CO2 generator
  • light=
  • light can get through the glass
  • lamps provide light during the night
  • temperature=
  • glasshouses trap heat energy from the sunlight which also warms the air
  • heating and cooling systems can also be used to keep a constant optimum temperature
126
Q

what are some limiting factors of the Calvin cycle and what do they lead to?

A

-light intensity
-temperature
-CO2 concentration
=can affect the levels of glycerate 3-phosphate (GP), ribulose bisphosphate (RuBP) and triose phosphate (TP)

127
Q

how does low light intensity impact the Calvin cycle?

A
  • the products of the light-dependent stage (reduced NADP and ATP) will be in short supply
  • this means that conversion of GP to TP and RuBP is slow
  • so the level of GP will rise as it’s still being made, but isn’t being used up as quickly
  • the level of TP and RuBP will fall as they’re used up to make GP, but aren’t being remade as quickly
128
Q

draw a graph showing the effect of light intensity on the levels of GP, RuBP and TP

A

insert pic page page 405 CGP

129
Q

what effect does changes in temperature have on the Calvin cycle?

A
  • all the reactions in the Calvin cycle are catalysed by enzymes (e.g. RuBisCO)
  • at low temps, all he reactions will be slower as the enzymes work slower
  • this means the levels of RuBP, GP and TP will fall

-GP, TP and RuBP are affected in the same way at very high temps, because the enzymes will start to denature

130
Q

what impact does low CO2 concentration have on the Calvin cycle?

A
  • at low CO2 concs, conversion for RuBP to GP is also slow as there’s less CO2 to combine with RuBP GP
  • so the levels of RuBP will rise as it’s still being made , but isn’t being used up
  • the levels of GP and TP will as they’re used to make RuBP, but aren’t being remade
131
Q

what are data loggers?

A

data loggers are electronic devices that record data over time using sensors

132
Q

what is recorded using data loggers?

A

physical properties are recorded such as light intensity, temp, pressure, pH ( which can be used as a measure of CO2 conc), and humidity

133
Q

how is data from a data logger produced?

A

readings can be displayed in graphical form or on a spreadsheet

134
Q

what are data loggers equipped with?

A

they are usually equipped with a microprocessor (which inputs digital data) and internal memory for data storage

135
Q

how do data loggers interact with computers?

A

-data loggers usually interface with a computer using specialised software

136
Q

how are readings taken with data loggers?

A
  • readings are taken with high degrees of accuracy and can be taken over long periods of time.
  • they can be set to be take many readings in a short period of time or used when there is a risk involved, for example, extreme cold or heat

-the software can be set to take readings at desired intervals fro the required length of time

137
Q

how can the factors affecting the rate of photosynthesis be investigated?

A

using a live pond weed, such as Elodea (Canadian pondweed)

138
Q

how can the rate of photosynthesis be estimated?

A

-by calculating the rate of oxygen produced, carbon dioxide used, or increase in dry mass of a plant

139
Q

in an investigation for the factors that affect the rate of photosynthesis, what can be used to provide CO2?

A

sodium hydrogen carbonate

140
Q

what are some conditions for investigating factors affecting the rate of photosynthesis?

A
  • the pond weed should be kept illuminated before use
  • the apparatus should be left to equilibrate for 10 minutes or so before readings are taken
  • the oxygen sensor may also need to be calibrated using the oxygen concentration of air (21%)
141
Q

draw a diagram summarising photosynthesis?

A

insert pic page 473 KERBOODLE

142
Q

what does having more than 1 type of pigment do?

A

it increases the range of wavelength of light that a plant can absorb

143
Q

in addition to photosynthetic pigments, what else do plants have in their leaves?

A
  • some plants also have other pigments in their leaves, which play other essential roles, e.g. protecting the leaves from excessive UV radiation
  • different species of plants contain different proportions and mixtures of pigments
144
Q

how can you extract and separate a sample of pigments form the leaves of plants?

A

using thin-layer chromatography (TLC)

145
Q

how can you identify the pigments present in a sample form the leaves in a plant?

A

-by calculating their Rf values

146
Q

what is a Rf value?

A

an Rf value is the distance a substance has moved through the stationary phase in relation to the solvent

147
Q

how are we able to identify the exact pigment from only the Rf value?

A

each pigment has a specific Rf value, under specific conditions, which can be looked up in a database

148
Q

what are the different areas in TLC?

A
  • TLC involves a mobile phase (in this case a liquid solvent)
  • a stationary phase (in TLC, this is a chromatography plate- a solid plate of glass or plastic with a thin layer of gel, which the pigments can travel through, on top
149
Q

describe the 7 steps involved in thin-layer chromatography

A

1- grind up several leaves (spinach) with some anhydrous sodium sulphate, then add a few drops of propanone

2-transfer the liquid into a test tube, add some petroleum ether and gently shake the tube. 2 distinct layers will from in the liquid- the top layer is the pigments mixed in with the petroleum ether

3-transfer some of the liquid from the top layer into a second test tube with some anhydrous sodium sulfate

4-draw a horizontal pencil line near the bottom of a chromatography plate. Build up a concentrated spot of the liquid form step 3 on the line by applying several drops, ensuring each one is dry before the next is added. This is the point of origin.

5-once the point of origin is completely dry, put the plat into a glass beaker with some prepared solvent (e.g. a mixture of propanone, cyclohexane and petroleum ether)- just enough so that the point of origin is a little bit above the solvent.
Put a lid on a beaker and leave the plate to develop. As the solvent spreads up the plate, the different pigments (solutes) move with it, but at different rates- so they separate.

6-when the solvent has nearly reached the top, take the plate out and mark the solvent front (the furthest point the solvent has reached) with a pencil and leave the plate to dry in a well-ventilated place.

7-there should be several new coloured spots on the chromatography plate between the point or origin and the solvent front. These are the separated pigments.

You can calculate their Rf values and then identify them by looking them up in the database

150
Q

how do you calculate the Rf value?

A

Rf value= distance moved by the solute / distance moved by the solvent

151
Q

describe the 6 step method that can be used to measure the effect of flight intensity on photosynthesis

A

1- a source of white light is placed at a specific distance from the pondweed

2-the pondweed is left to photosynthesis fro a set amount of time. As it photosynthesises, the oxygen released will collect i the capillary tube

3-at the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured. This is proportional to the column of O2 produced.

4- Any variable that could affect the results should be controlled.

5-the experiment is repeated and the average length of gas bubble is calculated, to make the results more precise.

6-the whole experiment is then repeated with the light source placed at different distances from the pondweed

152
Q

how can you adjust the apparatus used in the experiment to measure the effect of light intensity on photosynthesis, to measure the effect of temp and CO2 on photosynthesis?

A

e. g.
- the test tube of pondweed is put into a beaker of water at a set temp and CO2 is bubbled into the test tube (then the experiment’s repeated with diff temps of water/ concentrations of CO2)

153
Q

what is something you need to know in order to work out the exact volume of O2?

A

you need to know the radius of the capillary tube

154
Q

what is a way of measuring the volume of O2?

A

by counting the number of small O2 bubbles released by the pondweed, but this is less accurate

155
Q

draw + label the apparatus for the experiment used to measure the effect of limiting factors on photosynthesis

A

insert pic page 408 CGP

156
Q

draw + label the apparatus for the thin-layer chromatography (TLC) experiment

A

insert pic page 407 CGP

157
Q

draw a diagram showing the transfer of energy through the ecosystem

A

insert pic page 460 KERBOODLE

158
Q

compare respiration and photosynthesis (6)

A 
REACTANTS:
respiration= glucose and oxygen
photosynthesis= water and CO2
PRODUCTS:
respiration= water and glucose
photosynthesis= glucose and oxygen
PURPOSE:
respiration= release energy
photosynthesis= trap energy
159
Q

what are the 2 ways that electrons are raised to higher energy levels, or excited?

A

1- electrons present in pigment molecules (e.g. chlorophyll) are excited by absorbing light from the sun

2-high energy electrons are released when chemical bonds are broken in respiratory substrate molecules (e.g. glucose)

160
Q

what happens to the electrons when they’re excited?

A

the excited electrons pass into an electron transport chain and are used to generate a proton gradient

161
Q

what is an electron transport chain made up of and how is the proton gradient maintained?

A
  • an electron chain is made up of a series of electron carriers, each with progressively lower energy levels.
  • As high energy electrons move from one carrier in the chain to another, energy is released.
  • This is used to pump protons across a membrane, creating a concentration difference across the membrane and therefore a proton gradient.
  • the proton gradient is maintained as a result of the impermeability of the membrane to hydrogen ions.
162
Q

how can the protons move back through the membrane down their concentration gradient?

A

through hydrophilic membrane channels linked to the enzyme ATP synthase (catalyses the formation of ATP). The flow of protons through these channels provides the energy used to synthesise ATP (from ADDP and Pi)

163
Q

what is the difference between autotrophic and heterotrophic organisms?

A
  • autotrophic organisms are organisms that can photosynthesise, like plants and algae
  • heterotrophic organisms are organisms like animals that obtain complex organic molecules by eating other (heterotrophic and/or autotrophic) organisms
164
Q

draw the structure of a vertical section through a dicotyledonous leaf

A

insert pic page 467 KERBOODLE

165
Q

draw the structure of mesophyll cells

A

insert pic page 467 KERBOODLE

166
Q

describe the 2 stages of photosynthesis

A
  • light-dependent stage= energy from sunlight is absorbed and used to form ATP. Hydrogen from water is used to reduce coenzyme NADP to reduced NADP
  • light-independent stage= hydrogen from reduced NADP and CO2 is used to build organic molecules, such as glucose. ATO supplies the required energy.

OCR A level Biology HJ (23 decks)

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