Topic 2/8 - Part 3 Flashcards

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1
Q

Define cellular respiration

A
  • Controlled release of energy from organic compounds to produce ATP
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2
Q

ATP

A
  • Adenosine tri-phosphate

- Energy is immediately available and is released by splitting ATP into ADP and phosphate

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3
Q

State the molecular formula of glucose

A

C6H12O6

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4
Q

State the equation for cellular respiration

A

glucose + 6 oxygen –> 6 water + 6 carbon dioxide + 38 ATP

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5
Q

Explain when anaerobic respiration is useful

A
  • When a short but rapid burst of ATP production is needed
  • When oxygen supplies run out in respiring cells
  • In environments that are deficient in oxygen, for example waterlogged soils.
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6
Q

What is the result of anaerobic respiration in humans and animals

A
  • Lactate

- Net 2 ATP

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7
Q

What is the result of anaerobic respiration in yeasts and plants

A
  • Ethanol and Carbon dioxide

- Net 2 ATP

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8
Q

Explain the commercial use of yeasts

A
  • Yeast is added to dough to create bubbles of gas, so that the baked bread has a lighter texture
  • Bioethanol can be used as a renewable energy source (ethanol produced by living organisms)
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9
Q

Explain anaerobic respiration in humans

A
  • Anaerobic respiration can supply ATP very rapidly for a short period of time
  • Maximize the power of muscle contractions during exercises
  • Anaerobic respiration produces lactate; increase [lactate] is toxic, and there’s a limit to the amount the body can tolerate
  • Short timescale for maximum muscle activity
  • Lactate requires oxygen to be broken down after exercise
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10
Q

Outline the advantage of aerobic respiration

A
  • Yields more ATP per glucose (theoretically 38 ATP)

- Does not produce lactate

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11
Q

How can one measure the rate of cellular respiration?

A
  • respirometer
    guidance:
  • an alkali is used to absorb carbon dioxide, so reductions in volume are due to oxygen use
  • temperatures should be kept constant to avoid volume changes due to temperature fluctuations
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12
Q

What is meant by oxidation and reduction? How is this related to cellular respiration?

A
  • oxidation is the loss of eletrons froma substance
  • reduction is the gain of electrons
  • cellular respiration involves the oxidation and reduction of compounds
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13
Q

Explain phosphorylation

A
  • the addition of a phosphate molecule to an organic molecule
  • makes molecules less stable and thus more likley to react
  • phosphorylation can be said to activate the molecule
  • the hydrolysis of ATP releases energy to the environment and is therefore termed an exergonic reaction
  • many chemical reactions in the body are endergonic and require energy to proceed; thus, if the hydrolysis of ATP is coupled with the endergonic reacions, the endergonic reaction can proceed
  • many metabolic reactions are coupled to the hydrolysis of ATP
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14
Q

List the processes of aerobic cellular respiration

A
  1. Glycolysis
  2. Link reaction
  3. Krebs cycle
  4. Electron transport chain
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15
Q

Glycolysis

A
  • gives a small net gain of ATP without the use of oxygen
  • made up of many small steps (metabolic pathway); in the first step, ATP is used in the phosphorylation of sugar
  • ultimately, each molecule of glucose is converted into two molecules of pyruvate
  • results in 2 net ATP, 2 NADH
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16
Q

What happens to the pyruvate produced in glycolysis?

A
  • in aerobic cellular respiration, pyruvate is decarboxylized and oxidized
  • if oxygen is available, the pyruvate is absorbed into the mitochondrion where it is fully oxidized through a series of steps; the first step is the link reaction
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17
Q

Link reaction

A
  • pyruvate is moved into the mitochondrion matrix
  • pyruvate is decarboxylized and oxidized to become acetyl-CoA
  • two high energy electrons are removed from the pyruvate and react with NAD+ to produced reduced NAD
  • it is called the link reaction because it links glycolysis with the Krebs cycle
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18
Q

Krebs Cycle

A
  • the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers
  • two decarboxylizations and four oxidations occur in the Kreb’s cycle
  • most of the energy released in the oxidations of the Kreb’s cycle is used to reduce hydrogen carriers (NAD+ and FAD)
  • the energy therefore remains in chemical form and can be passed on to the final part of aerobic cellular respiration: oxidative phosphoryliation
  • in every turn of the cycle, the production of reduced NAD occurs 3 times, decarboxylation occurs twice and the reduction of FAD occurs once; one ATP is also produced
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19
Q

Define oxidative phosphorylation

A
  • the release of energy stored within the reduced hydrogen carriers (NAD+ / FAD) in other to synthesize ATP by the electron transport chain
  • called oxidative phosphorylation because the energy to synthesise ATP is derived from the oxidation of hydrogen carriers
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20
Q

List the 3 steps of oxidative phosphoylation

A
  1. Proton pumps create an electrochemical gradient (proton motive force)
  2. ATP synthase uses the subsequent diffusion of protons (chemiosmosis) to synthesise ATP
  3. Oxygen accepts electrons and protons to form water
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21
Q

Chemiosmosis in cellular respiration

A
  • protons diffuse through ATP synthase to produce ATP
  • the proton motive force will cause H+ ions to move down their electrochemical gradient and diffuse back into matrix
  • this diffusion of protons is called chemiosmosis and is facilitated by the transmembrane enzyme ATP synthase
  • as the H+ ions move through ATP synthase they trigger the molecular rotation of the enzyme, synthesising ATP
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22
Q

Mitochondrial ETC

A
  • eletron transport chain
  • located on the inner mitochondrial membrane
  • where oxidative phosphoylation/chemiosmosis occurs
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23
Q

What is the significance of oxygen in the mitochondrial ETC?

A
  • needed to bind with the free protons to form water to maintain the hydrogen gradient
  • it is the final electrona acceptor in the mitochondrial electron transport chain
  • the reduction of the oxygen molecule involves both accepting electrons and forming a covalent bond with hydrogen
  • by using up hydrogen, the proton gradient across the inner mitochondrial membrane is maintained so chemiomosis can continue
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24
Q

Outline the three steps of oxidative phosphorylation

A
  1. Generating a proton notive force
    - The hydrogen carriers (NADH and FADH2) are oxidised and release high energy electrons and protons
    - The electrons are transferred to the electron transport chain, which consists of several transmembrane carrier proteins
    - As electrons pass through the chain, they lose energy – which is used by the chain to pump protons (H+ ions) from the matrix
    - The accumulation of H+ ions within the intermembrane space creates an electrochemical gradient (or a proton motive force)
  2. ATP synthesis via chemiosmosis
    - The proton motive force will cause H+ ions to move down their electrochemical gradient and diffuse back into matrix
    - This diffusion of protons is called chemiosmosis and is facilitated by the transmembrane enzyme ATP synthase
    - As the H+ ions move through ATP synthase they trigger the molecular rotation of the enzyme, synthesising ATP
  3. Reduction of oxygen
    - In order for the electron transport chain to continue functioning, the de-energised electrons must be removed
    - Oxygen acts as the final electron acceptor, removing the de-energised electrons to prevent the chain from becoming blocked
    - Oxygen also binds with free protons in the matrix to form water – removing matrix protons maintains the hydrogen gradient
    - In the absence of oxygen, hydrogen carriers cannot transfer energised electrons to the chain and ATP production is halted
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25
Q

Give an overview of the process of oxidative phosphorylation

A
  • Hydrogen carriers donate high energy electrons to the electron transport chain (located on the cristae)
  • As the electrons move through the chain they lose energy, which is transferred to the electron carriers within the chain
  • The electron carriers use this energy to pump hydrogen ions from the matrix and into the intermembrane space
  • The accumulation of H+ ions in the intermembrane space creates an electrochemical gradient (or a proton motive force)
  • H+ ions return to the matrix via the transmembrane enzyme ATP synthase (this diffusion of ions is called chemiosmosis)
  • As the ions pass through ATP synthase they trigger a phosphorylation reaction which produces ATP (from ADP + Pi)
  • The de-energised electrons are removed from the chain by oxygen, allowing new high energy electrons to enter the chain
  • Oxygen also binds matrix protons to form water – this maintains the hydrogen gradient by removing H+ ions from the matrix
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26
Q

Explain the structure and function of mitochondria in relation to its role in cellular respiration

A

The structure of the mitochondrion is adapted to the function it performs:

  1. Outer membrane – the outer membrane contains transport proteins that enable the shuttling of pyruvate from the cytosol
  2. Inner membrane – contains the electron transport chain and ATP synthase (used for oxidative phosphorylation)
  3. Cristae – the inner membrane is arranged into folds (cristae) that increase the SA:Vol ratio (more available surface)
  4. Intermembrane space – small space between membranes maximises hydrogen gradient upon proton accumulation
  5. Matrix – central cavity that contains appropriate enzymes and a suitable pH for the Krebs cycle to occur
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27
Q

What technique can be used to produce images of active mitochondria?

A
  • electron tomography has allowed 3D images of the interior of mitochondria to be made
28
Q

Define photosynthesis

A

the production of carbon compounds in cells using light energy

29
Q

State the equation for photosynthesis

A

6 water + 6 carbon dioxide + solar energy –> glucose + 6 oxygen

30
Q

How can photosynthetic pigments be separated?

A
  • chromatography
    guidance:
  • paper chromatography can be used, but thin layer chromatography gives better results
31
Q

State the wavelength range for visible light and compare the wavelength of red and purple light

A
  • 400 - 700 nm
  • Red light has the longest wavelength
  • Violet light has the shortest wavelength
32
Q

State the colour of light that chlorophyll is the most efficient at absorbing, and the colour for least efficient

A
  • Chlorophyll is more efficient at absorbing red and blue light, and least efficient at green light
  • Therefore most plants are green (because they reflect green light)
33
Q

Photolysis

A
  • the splitting of water molecules to release electrons needed in other stages
  • all of the oxygen generated in photosynthesis comes from photolysis of water
  • generates electrons for use in light-dependent reactions

water –> 4 electrons + 4 protons (hydrogen ions) + oxygen

34
Q

Explain how photosynthesis led to changes in the Earth’s geology

A
  • Only one significant source of oxygen gas exists in the known universe – biological photosynthesis
  • Before the evolution of photosynthetic organisms, any free oxygen produced was chemically captured and stored
  • Approximately 2.3 billion years ago, photosynthetic organisms began to saturate the environment with oxygen
  • This led to changes in the Earth’s atmosphere, oceans, rock deposition and biological life
35
Q

Oultine the changes in Earth’s oceans as a result of photosynthesis

A
  • Earth’s oceans initially had high levels of dissolved iron (released from the crust by underwater volcanic vents)
  • When iron reacts with oxygen gas it undergoes a chemical reaction to form an insoluble precipitate (iron oxide)
  • When the iron in the ocean was completely consumed, oxygen gas started accumulating in the atmosphere
36
Q

Ouline the changes in Earth’s atmosphere as a result of photosynthesis

A
  • For the first 2 billion years after the Earth was formed, its atmosphere was anoxic (oxygen-free)
  • The current concentration of oxygen gas within the atmosphere is approximately 20%
37
Q

Ouline the changes in Earth’s rock deposition as a result of photosynthesis

A
  • The reaction between dissolved iron and oxygen gas created oceanic deposits called banded iron formations (BIFs)
  • These deposits are not commonly found in oceanic sedimentary rock younger than 1.8 billion years old; this likely reflects the time when oxygen levels caused the near complete consumption of dissolved iron levels
  • As BIF deposition slowed in oceans, iron rich layers started to form on land due to the rise in atmospheric O2 levels
38
Q

Ouline the changes in Earth’s biological life as a result of photosynthesis

A

Free oxygen is toxic to obligate anaerobes and an increase in O2 levels may have wiped out many of these species
Conversely, rising O2 levels was a critical determinant to the evolution of aerobically respiring organisms

39
Q

Is photosynthesis endothermic or exothermic? Explain your reasoning

A
  • endothermic because photosynthetic reactions requires an input of energy (solar energy)
40
Q

List three possible limiting factors on the rate of photosynthesis

A
  1. Temperature
  2. Light intensity
  3. Carbon dioxide concentration
41
Q

How can water free of carbon dioxide be produced (for use in photosynthetic experiments)?

A
  • boiling and cooling the water
42
Q

What are some common features of chloroplasts?

A
  • a double membrane forming the outer chloroplast envelope
  • an extensive system of internal membranes called thylakoids, which are an intense green colour
  • small fluid-filled spaces inside the thylakoids
  • a colourless fluid around the thylakoids called stroma that contains many different enzymes
  • in most chloroplasts, there are stacks of thylakoids called grana,
  • if a chloroplast has been photosynthesizing rapidly, then there may be starch grains or liquid droplets in the stroma
43
Q

Where do light-dependent reactions take place?

A
  • intermembrane space of the thylakoids, which is located in the chloroplast
44
Q

What are the products of the light-dependent reactions?

A
  • reduced NADP and ATP, which serve as energy sources for the light-independent reactions
45
Q

Where do light-independent reactions take place?

A
  • the stroma, which is located in the chloroplast
46
Q

List the steps in the light-independent reactions of photosynthesis

A

Note: the light indepndent reactions are collectively known as the Calvin cycle

Steps:

  1. Carboxylation of ribulose bisphosphate
  2. Reduction of glycerate-3-phosphate
  3. Regeneration of ribulose bisphosphate
47
Q

Outline the steps of the Calvin cycle (light independent reactions)

A

The Calvin cycle outlines the events that result in the formation of organic molecules from inorganic sources (CO2)

  • Ribulose bisphosphate (RuBP) is carboxylated by carbon dioxide (CO2) to form a hexose biphosphate compound
  • The hexose biphosphate compound immediately breaks down into molecules of glycerate-3-phosphate (GP)
  • The GP is converted by ATP and NADPH into molecules of triose phosphate (TP)
  • TP can be used to form organic molecules or can be recombined by ATP to reform stocks of RuBP
48
Q

What is the role of rubisco in photosynthesis?

A
  • acts as a catalyst for the carboxylation of RuBP (RuBP reacts with carbon dioxide to produce two molecules of glycerate 3-phosphate)
  • the stroma contains large amounts of rubisco to maximize carbon fixation
49
Q

RuBP

A
  • RuBP is both consumed and regenerated through the Calvin cycle
  • three RuBP react with carbon dioxide to form six glycerate 3-phosphate which will ultimately become six triose phosphate through the Calvin cycle, five of which can then be used for the regeneratation of RuBP and one for the production of carbohydrates
50
Q

What is the role of glycerate 3-phosphate in photosynthesis?

A
  • reduced to triose phosphate using reduced NADP and ATP
  • hydrogen must be added by a reduction reaction
  • ATP provides the energy required to perform the reduction and NADP provides the hydrogen atoms resulting in triose phosphate
51
Q

What is the role of triose phosphate in photosynthesis?

A
  • used to regenerate RuBP and to to produce carbohydrates
  • if 3 RuBP are used, 6 triose phosphates are produced; 5 triose phosphates are required to regenerate the 3 RuBP
  • 1 triose phosphate is thus available for conversion to carbohydrates
  • therefore, 6 turns of the Calvin cycle is required to produce one molecule of glucose (which requires 6 triose phosphates)
52
Q

Outline the three steps of the light-dependent reactions in photosynthesis

A
  1. Excitation of photosystems by light energy
    - Photosystems are groups of photosynthetic pigments (including chlorophyll) embedded within the thylakoid membrane
    - Photosystems are classed according to their maximal absorption wavelengths (PS I = 700 nm ; PS II = 680 nm)
    - When a photosystem absorbs light energy, delocalised electrons within the pigments become energised or ‘excited’
    - These excited electrons are transferred to carrier molecules within the thylakoid membrane
  2. Production of ATP via an ETC
    - Excited electrons from Photosystem II (P680) are transferred to an electron transport chain within the thylakoid membrane
    - As the electrons are passed through the chain they lose energy, which is used to translocate H+ ions into the thylakoid
    - This build up of protons within the thylakoid creates an electrochemical gradient, or proton motive force
    - The H+ ions return to the stroma (along the proton gradient) via the transmembrane enzyme ATP synthase (chemiosmosis)
    - ATP synthase uses the passage of H+ ions to catalyse the synthesis of ATP (from ADP + Pi)
    - This process is called photophosphorylation – as light provided the initial energy source for ATP production
    - The newly de-energised electrons from Photosystem II are taken up by Photosystem I
  3. Reduction of NADP+ and the photolysis of water
    - Excited electrons from Photosystem I may be transferred to a carrier molecule and used to reduce NADP+
    - This forms NADPH – which is needed (in conjunction with ATP) for the light independent reactions
    - The electrons lost from Photosystem I are replaced by de-energised electrons from Photosystem II
    - The electrons lost from Photosystem II are replaced by electrons released from water via photolysis
    - Water is split by light energy into H+ ions (used in chemiosmosis) and oxygen (released as a by-product)
53
Q

Give an overview of the light-dependent reactions in photosynthesis

A
  • The light dependent reactions occur within the intermembrane space of the thylakoids
  • Chlorophyll in Photosystems I and II absorb light, which triggers the release of high energy electrons (photo activation)
  • Excited electrons from Photosystem II are transferred between carrier molecules in an electron transport chain
  • The electron transport chain translocates H+ ions from the stroma to within the thylakoid, creating a proton gradient
  • The protons are returned to the stroma via ATP synthase, which uses their passage (via chemiosmosis) to synthesise ATP
  • Excited electrons from Photosystem I are used to reduce NADP+ (forming NADPH)
  • The electrons lost from Photosystem I are replaced by the de-energised electrons from Photosystem II
  • The electrons lost from Photosystem II are replaced following the photolysis of water
  • The products of the light dependent reactions (ATP and NADPH) are used in the light independent reactions
54
Q

Differentiate between Photosystem I and Photosystem II

A
  • photosystem II is where the light-dependent reactions of photosynthesis begin, as it removes an electron from water molecules and break it down to oxygen and hydrogen
  • the excited electron produces ATP as it returns to its rest state
  • at this point, the electron is once again excited by the photosystem I to a much higher energy level and produces a NADPH molecule which is used by the Calvin cycle.
  • photosystem I is very receptive to light waves at the 700 nm wavelength whilst photosystem II is very receptive to light wavelengths of around 680 nm.
55
Q

Photoactivation

A

the activation or control of a chemical, chemical reaction, or organism by light, as the activation of chlorophyll by sunlight during photosynthesis

56
Q

Plastoquinone

A
  • an electron acceptor associated with Photosystem II in photosynthesis.
  • it accepts two electrons and is reduced to Plastoquinol
  • acts as an electron and energy carrier in the electron transport process; carries the pair of excited electrons from the reaction centre of Photosystem II to the start of the chain of electron carriers
57
Q

Photophosphorylation

A
  • the production of ATP by the light dependent reactions
  • carried out by thylakoids
  • may be either a cyclic process or a non-cyclic process
58
Q

Cyclic phosphorylation

A
  • Cyclic photophosphorylation involves the use of only one photosystem (PS I) and does not involve the reduction of NADP+
  • When light is absorbed by Photosystem I, the excited electron may enter into an electron transport chain to produce ATP
  • Following this, the de-energised electron returns to the photosystem, restoring its electron supply (hence: cyclic)
  • As the electron returns to the photosystem, NADP+ is not reduced and water is not needed to replenish the electron supply
59
Q

Non-Cyclic phosphorylation

A
  • Non-cyclic photophosphorylation involves two photosystems (PS I and PS II) and does involve the reduction of NADP+
  • When light is absorbed by Photosystem II, the excited electrons enter into an electron transport chain to produce ATP
  • Concurrently, photoactivation of Photosystem I results in the release of electrons which reduce NADP+ (forms NADPH)
  • The photolysis of water releases electrons which replace those lost by Photosystem II (PS I electrons replaced by PS II)
60
Q

Differentiate between cyclic phosphorylation with non-cyclic phosphorylation

A

Cyclic phosphorylation

  • only PS I involved
  • water is not required
  • oxygen is not evolved
  • NADPH is not syntheiszed
  • used to produce additional ATP in order to meet cell energy demands

Non-cyclic phosphorylation

  • PS I and PS II are both involved
  • photolysis of water is required
  • oxygen is evolved
  • NADPH is synthesized
  • products can be used for the light indepedent reactions
61
Q

What structures does a thylakoid membrane contain?

A
  • photosystem II
  • photosystem I
  • ATP synthase
  • a chain of electron carriers
62
Q

What contibutes to the proton gradient across the thylakoid membrane?

A
  • excited electrons from photosystem II are used to create a proton gradient
  • photolysis, which occurs in the fluid inside the thylakoids, also contributes to the proton gradient
63
Q

Chemiosmosis in photosynthesis

A
  • similar to the chemiosmosis in cellular respiration
  • protons travel across the membrane, down the concentration gradient, by passing through the enzyme ATP synthase
  • the energy released by the passage of the protons through the ATP synthase is used to make ATP from ADP + inorganic phosphate
  • when the electrons reach the end of the chain of carriers, they are passed to plastocyanin which is a water-soluable electron acceptor in the fluid inside the thylakoids
  • reduced plastocyanin is needed to transfer the electron to photosystem I
64
Q

Explain how NADP is reduced in Photosystem I

A
  • chlorophyll molecules within PS I absorb light energy and pass it to the special two chlorophyll molecules in the reaction centre
  • this raises an electron in one of the chlorophylls to a high energy level (photoactivation)
  • the excited electron passes along a chain of carriers in PS I, at the end of which it is passed to ferredoxin (a protein in the fluid outside the thylakoid)
  • two molecules of ferredoxin are used to reduce NADP to form reduced NADP
  • an electron carried by plastocyanin, which is obtained from PS II, replaces the electron that PS I donated to the chain of carriers
65
Q

What is the role of reduced NADP in photosynthesis?

A
  • needed for light-independent reactions of photosynthesis (Calvin cycle)
  • carries a pair of electrons that can be used to carry out reduction reactions
66
Q

Carbon fixation

A
  • the conversion process of inorganic carbon (carbon dioxide) to organic compounds by living organisms
  • ie. Calvin cylce of photosynthesis
67
Q

Calvin’s lollipop

A
  • Radioactive carbon-14 is added to a ‘lollipop’ apparatus containing green algae (Chlorella)
  • Light is shone on the apparatus to induce photosynthesis (which will incorporate the carbon-14 into organic compounds)
  • After different periods of time, the algae is killed by running it into a solution of heated alcohol (stops cell metabolism)
  • Dead algal samples are analysed using 2D chromatography, which separates out the different carbon compounds
  • Any radioactive carbon compounds on the chromatogram were then identified using autoradiography (X-ray film exposure)
  • By comparing different periods of light exposure, the order by which carbon compounds are generated was determined
  • Calvin used this information to propose a sequence of events known as the Calvin cycle (light independent reactions)