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Biology > C1.3: Photosynthesis > Flashcards

C1.3: Photosynthesis Flashcards

1
Q

Outline how light energy is converted to chemical energy in carbon compounds.

A

Chlorophyll captures light energy from the sun to create chemical energy in the form of ATP

  • This can be used to synthesise organic compounds like carbs, proteins, lipids, nucleic acids
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2
Q

Draw a flowchart to illustrate the energy conversions performed by living organisms.

A

Light energy to chemical energy in photosynthesis.

Chemical energy to kinetic energy in muscle contraction.

Chemical energy into electrical energy in nerve cells.

Chemical energy into heat energy in heat-generating adipose tissue.

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3
Q

List three reasons why living organisms need energy for cell activities.

A
  • Synthesising macromolecules like DNA
  • Pumping molecules or ions via active transport
  • Movement of things within the cell such as vesicles
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4
Q

What is the principal energy source in most ecosystems. ​

A

Sunlight

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5
Q

State the chemical equation for photosynthesis.

A

6CO2 + 6H2O –> C6H12O6 + 6O2

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6
Q

Outline the source of the atoms used to form glucose (C6H12O6) during photosynthesis.

A

A source of H is needed
- To access the H, it needs to be removed from the water thus, photolysis occurs

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7
Q

Define photolysis.

A
  • The splitting of water molecules using light energy during the light-dependent reactions of photosynthesis.
  • Releases: O2, e- and Protons
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8
Q

State the equation for photolysis

A

2H2O –> 4H+ + O2 + 4e-

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9
Q

State the source of the oxygen produced as a by-product in photosynthesis.

A

Oxygen is generated as a by-product of the splitting of water, photolysis

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10
Q

Define Paper chromatography

A
  • Paper chromatography is a technique that separates mixtures of substances based on the movement of different substances on a piece of paper by capillary action
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11
Q

State which parts of paper chromatography are the stationary phase and mobile phase

A
  • Stationary phase: the paper
  • Mobile phase: the solvent used to develop the chromatogram
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12
Q

Outline the process of separating pigments using chromatography.

A
  • Can be separated using paper chromatography
  • Pigments are first extracted from leaves using a suitable solvent that dissolves most of the plant pigments
  • A sample of the extract (fluid) is placed on chromatography paper and transferred to a container with the chromatography solvent
  • Pigments move at diff rates on the stationary phase and separate according to size to form a chromatogram
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13
Q

Identify pigments that result from chromatography by color and calculated Rf value. ​

A
  • Rf = Retention Factor
  • Formula: Rf = sample distance / solvent distance
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14
Q

State the range of wavelengths that fall within the visible spectrum.

A

400nm to 750nm

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15
Q

Outline the function of pigments.

A
  • Absorb the photons in the visible light spectrum and reflect the colour that we see
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16
Q

State the primary and accessory pigments found in chloroplasts.

A
  • Primary pigments: Chlorophylls - Chlorophyll a and Chlorophyll b (reflect green light)
  • Absorb wavelengths in the blue-violet and red regions
  • Accessory pigments: Carotenoids - Xanthophyll and b carotene (reflect yellow and orange light respectively)
  • Absorb wavelengths in the blue-violet regions
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17
Q

Explain why most plants look green.

A
  • Chlorophyll a and b, the main pigments capturing the photons, reflect green light and absorb wavelengths in the blue-violet and red regions of the light spectrum
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18
Q

Define the EM Spectrum

A
  • A range of frequencies and wavelengths of electromagnetic radiation emitted from the Sun
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19
Q

Sketch the chlorophyll pigment absorption spectrum, including both wavelengths and colors of light on the X-axis.​

A
  • X-axis: wavelength of light, Y-axis: Amount of light absorbed

Chlorophyll a:
- 2 peaks; one at 425 and one at 660
- remains somewhat constant in between

Chlorophyll b:
- 2 peaks; one exponential slope turning into a large one at 550 and one medium one at 625
- remains somewhat constant in between
- X-axis: wavelength of light, Y-axis: Amount of light absorbed

Carotenoid:
- one small trough after a straight line at 450 then a large narrow peak at 475
- goes back down to x-axis at 525

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20
Q

Why do carotenoids absorb both similar and different wavelengths of light to chlorophyll

A

This expands the range of wavelengths that can be absorbed form light for use in photosynthesis

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21
Q

Outline the comparison of Rf values (not numbers) for pigments involved in photosynthesis. What do the different Rf values of the pigments indicate?

A
  • Carotenoids have the highest Rf values (closest to 1)
  • Chlorophyll a has Rf values in betw. those of carotenoids and chlorophyll b
  • Chlorophyll b has a much lower Rf value than Carotenoids

Smaller Rf values indicate the pigment is less soluble and/or larger

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22
Q

Compare and contrast the action spectrum and absorption spectrum.

A

Action spectrum:
- measures the overall rate of photosynthesis against the wavelength of light
- X-axis is wavelength of light (nm)
- Y-axis is the rate of photosynthesis

Absorption spectrum:
- measures the wavelengths of light absorbed by each pigment
- X-axis is wavelength of light (nm)
- Y-axis is amount of light absorbed

Both:
- highest rates are at the blue and red wavelengths while the lowest rates occur at the green

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23
Q

Explain the shape of the curve of the photosynthesis action spectrum.

A
  • highest rates are at the blue and red wavelengths while the lowest rates occur at the green
  • This matches the absorption spectra of the photosynthetic pigments closely as it’s their ability to absorb light energy that allows photosynthesis to occur
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24
Q

Outline a technique for calculating the rate of photosynthesis by measuring either oxygen production or carbon dioxide consumption.

A
  • Use a water plant: Elodea
  • Oxygen produced can be counted as bubbles or collected in a measuring cylinder/gas syringe
  • Calculate the rate of photosynthesis: number of bubbles / 1 minute
  • Control and change temperatures using a water bath, light intensity can be controlled and changed by moving a primary light source closer or further away from the plant, CO2 conc. can be controlled and changed by using sodium hydrogen carbonate which can be dissolved in the water containing the plant.
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25
Q

Outline a technique, other than using plants, to measure the rate of photosynthesis

A
  • Use hydrogen carbonate indicator solution which will change colour as the conc. of CO2 changes
  • If the plant doesn’t photosynthesise and only respires: CO2 conc. will increase and the indicator turns more yellow
  • If the plant is photosynthesising, CO2 is absorbed and the indicator turns more purple
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26
Q

Define “limiting factor.”

A

A condition that, when in shortage, slows down rate of reaction. The main limiting factors of photosynthesis includes:
- light intensity
- conc. of CO2
- temperature

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27
Q

Explain how the following factors limit the rate of photosynthesis: temperature, light intensity, CO2 concentration.

A

Temperature:
- influences photosynthetic enzymes

Light intensity:
- required for chlorophyll photoactivation

CO2 conc:
- CO2 is a core substrate that is required

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28
Q

Identify manipulated (independent), responding (dependent) and controlled variables in experiments testing limiting factors on the rate of photosynthesis.

A

Independent / control:
- Control and change temperatures using a water bath,

  • light intensity can be controlled and changed by moving a primary light source closer or farther away from the plant
  • CO2 conc. can be controlled and changed by using sodium hydrogen carbonate which can be dissolved in the water containing the plant.

Dependent variable:
- Number of bubbles / 1 minute

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29
Q

Outline techniques for measuring the rate of photosynthesis while manipulating either temperature, light intensity, or CO2 concentration.

A

Manipulate temperature by:
- changing the temperature in the water bath

Manipulate light intensity by:
- moving a primary light source closer or further away from the plant

Manipulate CO2 conc. by:
- using sodium hydrogen carbonate which can be dissolved in the water containing the plant.

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30
Q

State the source of atmospheric carbon dioxide beyond the historical average of about 300 ppm.

A

Fossil Fuels

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31
Q

Explain the enclosed greenhouse experiments.

A

Enclosed Greenhouse experiments:
- CO2 can be carefully monitored or controlled
- Elevated CO2 levels can be created by burning fossil fuels
- If other conditions are controlled and there’s a controlled greenhouse without enriched CO2, the effect of CO2 can be measured by measuring the total biomass produced or the yield of fruits or vegetables grown.
- Limitations: There are natural factors and variables that are not able to be taken into account

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32
Q

Explain free-air carbon dioxide enrichment (FACE) experiments

A

Free-air CO2 Enrichment experiments:
- CO2 is released around a circular area
- Pipes surround the area and release CO2 continuously
- CO2 sensors within the area monitor CO2 levels ensuring elevated conc. are maintained
- This allows for a more natural way of measuring the impact of higher CO2 levels in the atmosphere
- Limitations: Very expensive experiment to carry out

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33
Q

Advantages and Disadvantages of Enclosed Greenhouse experiments

A

Adv:
- High level of control of environmental factors like light, temp, humidity, etc
- Reduced impact on the natural environments as they take place in a contained setting

Disadv:
- Limited ecological relevance as it may not accurately reflect real-world conditions

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34
Q

Advantages and Disadvantages of FACE experiments

A

Adv:
- Experiments occur in a natural setting allowing researchers to study the effects of specific factors
- Ability to study larger organisms like larger plants and trees

Disadv:
- Potential environmental impact due to introducing elevated levels of CO2 into the environment

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35
Q

List the questions that are addressed in carbon dioxide enrichment experiments.

A

How much food production there is going to be in the future:
- As future rates of photosynthesis and plant growth can be predicted using FACE experiments

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36
Q

Describe the arrangement of pigments into photosystems in membranes.

A
  • Molecular arrays of chlorophyll and accessory pigments within photosystems (found in thylakoid membranes)
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37
Q

Outline the advantage of pigments being arranged in photosystems as opposed to being dispersed.

A
  • Allows maximum absorption of light energy by the pigments

If the pigments were dispersed:
- Light energy would only be absorbed by individual pigments thus, there would not be enough energy to cause the emission of e-
- There would also be little conversion of that light energy into chemical energy due to the process being too inefficient

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38
Q

Describe the absorption of the different wavelengths of visible light by the 3 different pigments found in the chloroplast

A
  • All 3 pigments are poor absorbers of green light
  • Carotenoids are good absorbers in the blue-violet region in the spectrum
  • Chlorophyll a is a good absorber in the blue-red including orange-red region in the spectrum
  • Chlorophyll b is a good absorber in the blue-red region in the spectrum
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39
Q

State the function of the reaction center pigment in a photosystem.

A
  • Reaction centres are protein complexes within photosystems where light energy is converted into chemical energy containing specialised chlorophyll molecules that can donate electrons directly into the ETC
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40
Q

State what photoactivation is

A
  • Photoactivation refers to the process where light energy activates pigments, leading to a photochemical reaction and the release of excited electrons.
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41
Q

Compare the peak absorbance of the reaction center chlorophyll molecules of photosystem I and photosystem II.

A

Photosystem I:
- It is the most sensitive to light wavelengths of 700nm

Photosystem II:
- It is the most sensitive to light wavelengths of 680nm thus, it is the first one that is activated by light

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42
Q

Outline advantages of pigment molecules being arranged within a photosystem.

A
  • Only through the use of arrays of many pigment molecules can enough light be absorbed to photo activate the central chlorophyll molecule. Thus, hundreds of pigment molecules allows for a wider range of wavelengths to be absorbed
  • This causes the excitation and the release of e- that will provide energy for the rest of the light-dependent phase of photosynthesis.
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43
Q

Describe the role of photosystem II in photolysis.

A
  • Photolysis of water generates e- for use in the light-dependent reaction as it constantly replaces e- lost by photosystem II
44
Q

Outline the movement of electrons generated by photolysis of water at photosystem II.

A
  • Due to the release of e- from the chlorophyll molecule at the reaction centres of photosystem II, this creates a very unstable molecule in its oxidised state
  • Thus, as the reaction centre is in its oxidised state, it becomes a powerful oxidising agent and becomes the reason that photolysis occurs to donate their e- to the reaction centre therefore forming a proton gradient in the thylakoid lumen as more protons (H+) get formed thus, contributing to the high conc. of protons in the thylakoid lumen and acidic conditions
45
Q

State what the photolysis of water at photosystem II contribute to

A

Photolysis of water at photosystem II contributes to the proton gradient in the thylakoid lumen.

46
Q

What is the function of the acetone used in paper chromatography to separate photosynthetic pigments?

A

Photosynthetic pigments are non-polar substances that can’t be dissolved in water. Acetone is a non-polar solvent that can dissolve non-polar substances so that they can run up the paper strip.

47
Q

Outline the role of photosynthesis of the “Great Oxygenation Event” on early Earth.

A
  • Photolysis in cyanobacteria produced oxygen leading to the oxidation of iron (which existed in its reduced state) and other elements
  • Iron dissolved into the oceans and oxidised to iron oxide.
  • Oxygen started to then accumulate in the atm. allowing aerobic respiration to evolve in bacteria
  • Later, chloroplasts evolved by endosymbiosis from cyanobacteria
48
Q

Outline the evidence for the “Great Oxygenation Event” provided by banded iron formations.

A

pk

49
Q

Sketch a cross section of the thylakoid membrane, inclusive of photosystem II, ATP synthase, an electron transport chain (with Pq) and photosystem II.

A

pk

50
Q

Define chemiosmosis and photophosphorylation.

A

Chemiosmosis:
- The process by which energy stored in the proton gradient is used to produce ATP.

Photophosphorylation:
- The process of generating ATP using light energy. It occurs during the light-dependent reactions of photosynthesis

51
Q

State the movement of electrons generated by photosystem II

A

electrons generated by photosystem II pass from plastoquinone (Pq) through a chain of electron carrier molecules.

52
Q

Where do light-dependent reactions occur

A
  • Thylakoids; more specifically, the thylakoid lumen
53
Q

State what plastoquinone is (Pq) and its function

A
  • Functions as an electron carrier
  • Transports e- between 2 complexes of proteins in the thylakoid membrane of the chloroplast
54
Q

State what the energy released by the movement of e- is used for

A

The energy released by the movement of electrons is used to pump protons across the thylakoid membrane, from the stroma into the thylakoid lumen.

55
Q

State the result of the ETC

A

a proton gradient, with a high concentration of protons in the thylakoid lumen thus, contributing to acidic conditions

56
Q

Outline the generation of ATP by chemiosmosis as protons move down their concentration gradient through ATP synthase.

A
  • H+ ions (protons) are pumped from the stroma into the thylakoid inter-membrane space
  • Thylakoid membrane is impermeable to protons thus, H+ ions quickly accumulate, establishing an electrochemical gradient

-H+ ions diffuse through ATPSynthase forming a proton gradient thus, energy is released to phosphorylate ADP to ATP (Photophosphorylation occurs)

57
Q

State what ferredoxin is and its function

A

A protein found in chloroplasts that acts as an e- carrier in photosynthesis

58
Q

State what NADP is

A
  • Nicotinamide Adenine Dinucleotide Phosphate is an e- carrier
  • Accepts 2e- from photosystem I & 2H+ from stroma to become NADPH

(NAD is used in cellular respiration whereas, in the same way, NADP is used in photosynthesis - think of it like the P stands for Photosynthesis)

59
Q

Explain the flow of electrons in cyclic photophosphorylation

A
  • light energy causes the excitation of electrons from photosystem I (PSI) as photoactivation occurs
  • These electrons then move along the electron transport chain, pumping H+, establishing a proton gradient and generating ATP with ATP synthase.
  • The electrons will return to PSI after moving along the ETC, replacing those that were lost
60
Q

Explain the flow of electrons in non-cyclic photophosphorylation

A
  • light energy excites electrons in PSII ,as photoactivation occurs, which are then passed along the ETC, pumping H+ and generating ATP.
  • Photolysis occurs (2H2O —> 4H+ + 4e- + O2) and so the protons formed (H+) contribute to the high conc. gradient in the thylakoid lumen, e- formed replenish the e- in PSII that were lost and O2 formed which act as waste products of photosynthesis.
  • The e- get passed along the ETC
  • The electrons then enter PSI where they are re-energised with light energy thus, they get excited again and then, they are passed to ferredoxin which reduces NADP+ to NADPH.
  • Protons in thylakoid lumen (H+) flow down conc. gradient through ATP Synthase, ADP + P gets converted to ATP (Photophosphorylation occurs)
61
Q

State the function of photoactivation of the centre chlorophyll in photosystem I

A

Excites electrons which pass through a different electron transport chain.

62
Q

Outline the flow and function of electrons from photosystem I in cyclic photophosphorylation.

A
  • light energy causes the excitation of electrons from photosystem I (PSI).
  • These electrons then move along the electron transport chain, pumping H+, establishing a proton gradient and generating ATP with ATP synthase.
  • The electrons will return to PSI after moving along the ETC, replacing those that were lost
63
Q

Outline the flow and function of electrons from photosystem I in non-cyclic photophosphorylation.

A
  • light energy excites electrons in PSII, which are then passed along the ETC, pumping H+ and generating ATP.
  • The electrons then enter PSI where they are re-energised with light energy, passed to ferredoxin and then used to reduce NADP.
64
Q

State what the electrons in noncyclic photophosphorylation are used for and state what happens without this step

A

In noncyclic photophosphorylation, the electrons of photosystem I are used to reduce NADP+ to form NADPH.
- Without this step, the light-dependent stage of photosynthesis could not occur.

65
Q

State the function of the enzyme NADP reductase.

A

Catalyzes the reduction of NADP+ to NADPH using electrons obtained from the electron transport chain during photosynthesis.

66
Q

State the energy conversion in light-dependent reactions

A

the light-dependent reactions convert light energy into chemical energy in the form of ATP and NADPH

67
Q

Describe the structure of the thylakoid grana and stroma lamellae.

A

Structure of the Thylakoid Grana:
- Stacks of thylakoids that provide a large surface area to allow for as many PS’, ETCs and ATPSynthases as possible.

Structure of the Stroma Lamellae:
- The stacks of thylakoids are connected by multiple sheets of stroma lamellae

68
Q

Outline how the thylakoid functions as a system of interacting parts.

A
  • it allows the light-dependent stage of photosynthesis to occur effectively
  • This is because the membranes of the thylakoids have the photosystems, ETCs and ATP Synthases embedded in them
  • The space within the thylakoids allow for proton gradients to form as H+ ions are pumped into them.
  • Within the thylakoid space, photolysis occurs which releases Oxygen (waste product of Photosynthesis)
69
Q

State the location of the light-dependent reactions of photosynthesis, including photoactivation, photolysis, electron transport chain, chemiosmosis, and reduction of NADP.

A

Thylakoid membranes

70
Q

State the role of glycerate 3-phosphate

A
  • A 3-carbon molecule that is produced during the carbon fixation stage of the Calvin cycle.
  • It is a key intermediate in the conversion of inorganic carbon dioxide into organic compounds.
71
Q

State the role of Rubisco

A
  • Rubisco is the enzyme catalysing the addition of CO2 to RuBP
  • It is the most abundant enzyme on Earth
72
Q

Define carbon fixation and carboxylation.

A

Carbon Fixation:
- The conversion of inorganic Carbon (CO2 from atm) to organic Carbon by a living organism

(Carbon fixation) Carboxylation:
- Where CO2 gets added to a 5-carbon compound, ribulose bisphosphate (RuBP), catalyzed by the enzyme Rubisco, forming two 3-carbon compounds, glycerate 3-phosphate (G-3-P).

73
Q

State where carbon fixation occurs

A

In the chloroplast stroma

74
Q

State what happens to the 5-carbon molecule RuBP for it to form 2G-3-Ps

A

The 5-carbon molecule ribulose bisphosphate (RuBP) is carboxylated by CO2, forming two 3-carbon molecules called glycerate-3-phosphate (G-3-P).

75
Q

State the enzyme that catalyzes the carboxylation of RuBP

A

Ribulose bisphosphate carboxylase (rubisco).

76
Q

State the most abundant enzyme on Earth

A

The enzyme rubisco is the most abundant enzyme on Earth.

77
Q

State the effectiveness of rubisco at low concentrations of CO2.​

A
  • Rubisco is relatively ineffective at low conc. of CO2
78
Q

State the source of the carbon and oxygen atoms that become part of the carbohydrate molecule (ie C6H12O6) produced in photosynthesis.

A

Co2 that gets converted into Glucose (C6H12O6)

79
Q

State the source of the hydrogen atoms that become part of the carbohydrate molecule (ie C6H12O6) produced in photosynthesis.

A

H2O that is split during photolysis to produce Oxygen and Hydrogen

80
Q

State the relationship between ADP and NADPH

A

ATP (from the light-dependent reaction) provides the energy for NADPH (also from the light-dependent reaction) to reduce G-3-P forming a 3C carbohydrate, TP

81
Q

State where the synthesis of triose phosphate (TP) occurs

A

In the chloroplast stroma during light independent reactions

82
Q

State the role of triose phosphate

A
  • It’s a 3-C molecule that is produced
  • It is used to synthesise carbon compounds like glucose (a hexose monosaccharide) using ATP and NADPH
83
Q

Outline the formation of a hexose monosaccharide (ie glucose) from the triose phosphate produced in the light independent reactions.

A
  • Each G-3-P (glycerate 3-phosphate) is converted to Triose Phosphate which can synthesise carbon compounds such as hexose monosaccharides (glucose) using ATP and NADH
  • Each G-3-P molecule requires 1 ATP, which provides energy, and 1 NADPH, which reduces the G-3-P to triose phosphate with the addition of Hydrogen.
84
Q

Outline the reason that ribulose bisphosphate (RuBP) must be regenerated in the Calvin cycle.

A

It must be regenerated for the cycle to continue:
- Because RuBP is a 5-C compound and triose phosphate is a 3-C compound, we’re able to make 6 RuBP from 10 triose phosphates

  • Initially, 6 molecules of CO2 and 12 triose phosphates are made meaning only 2 of those can be used to synthesise Carbon compounds as the other 10 are required for the regeneration of RuBP which is the energy of 1 ATP molecule.
85
Q

State where 5 molecules of 3-C triose phosphate are used and for what purpose

A

in the Calvin Cycle, five molecules of 3-carbon triose phosphate (TP) are used to regenerate the three molecules of the 5-carbon ribulose bisphosphate (RuBP).

86
Q

State the number of turns in the Calvin Cycle needed to produce 1 molecule of a hexose monosaccharide (glucose)

A

6 turns

87
Q

State what is used to regenerate RuBP from Triose Phosphate (TP)

A

ATP

88
Q

State what the basis for carbon entering a food web is

A

carbon fixation during the light independent reactions is the basis for carbon entering a food web.

89
Q

Outline the formation of glucose, sucrose, starch and cellulose from the triose phosphate (TP) formed during photosynthesis.

A
  • Glucose gets converted to Sucrose for transport from leaves to other parts of the plant
  • Chloroplasts can also convert triose phosphate into fatty acids using enzymes of the glycolysis pathway and link reaction to produce acetyl CoA then link together 2C acetyl groups.

-

90
Q

State the 3 chronological steps in the Calvin cycle

A
    1. Carbon Fixation
    1. Reduction
    1. Regeneration
91
Q

Explain the first step of the Calvin Cycle

A

Carbon Fixation (Carboxylation):
- Rubisco catalyses the attachment of a CO2 molecule to a RuBP (5-C compound)

  • The 6-C compound formed is unstable and breaks down into two 3-C compounds (called Glycerate 3-Phosphate - G-3-P)
  • 1 cycle involves: 3 molecules of RuBP combined with 3 molecules of CO2 thus, making 6 molecules of G-3-P
92
Q

Explain the second step of the Calvin Cycle

A

Reduction of G-3-P:
- G-3-P gets converted to TP (triose phosphate) using NADPH and ATP generated by the light-dependent reactions

  • Reductions by NADPH transfers Hydrogen atoms to the compound while the hydrolysis of ATP provides energy
  • because 6 molecules of G-3-P got produced via carbon fixation, 6 molecules of TP are also produced in 1 cycle
93
Q

Explain the third step of the Calvin Cycle

A

Regeneration of RuBP:
- one of the 6 molecules of TP produced per cycle, 1 TP molecule can be used to form half a sugar molecule thus, 2 cycles are required to produce a single glucose monomer and more to produce polysaccharides (like starch)

  • The remaining 5 TP molecules recombine to regenerate stocks of RuBP (5 x 3C = 3 x 5C)
  • The regeneration of RuBP needs energy derived from the hydrolysis of ATP
94
Q

How many molecules of Triose Phosphate are produced from the fixation of 6 molecules of CO2? Explain

A
  • 12
  • Each molecule of CO2 forms 2 molecules of Triose Phosphate thus, 6 molecules of CO2
95
Q

To regenerate 12 molecules of RuBP, how many molecules of CO2, NADP and ATP are required?

A
  • 12 CO2 (x1)
  • 36 ATP (x3)
  • 24 NADP (x2)
96
Q

State what enzymes in plant cells can create and how

A

enzymes in plant cells can create fatty acids, glycerol, amino acids and nucleotides using metabolic pathways that can be traced back to the light-independent reactions of photosynthesis. ​

97
Q

List the major steps of the light-dependent and light-independent reactions of photosynthesis.

A

Major steps of the light-dependent reactions:
- Photolysis
- Light Absorption by the generation of excited e-
- Transport of e- by carriers
- ATPSynthesise by chemiosmosis
- Reduction of NADP

Major steps of the light-independent reactions:
- Carbon Fixation
- Synthesis of TP and other Carbon compounds (Reduction of G-3-P)
- Regeneration of RuBP

98
Q

What can occur in both light-independent and light-dependent reactions

A
  • The products of Light-dependent reactions are used in light-independent reactions
  • Both occur in photosynthesis
  • Both occur in chloroplasts
  • Both can occur in daytime
99
Q

Explain the process of light-dependent reactions

A
  • Take place in the thylakoid lumen and thylakoid membranes
  • Require light
  • Products are O2, NADPH (as NADP gets reduced, accepts excited electrons and H+ ions) and ATP
  • E- and H+ ions are required; supplied by photolysis of water (splitting of water)
  • E- that are lost by photoactivation of PSII are replenished by e- generated from the photolysis of water through non-cyclic photophosphorylation
  • Excited e- move from PSII to PSI through ETC to facilitate the pumping of protons thus, generating a proton gradient
  • ATP is synthesised using ATP Synthase as a result of chemiosmosis occurring; excited electrons are pumped from the thylakoid lumen (high conc. of excited e- and H+ ions due to photolysis) to the stroma
  • E- that return to PSI have reduced energy thus, get re-excited by the further absorption of light required for the reduction of NADP to form NADPH
100
Q

Explain the process of light-independent reactions (aka Calvin Cycle)

A
  • Takes place in Stroma
  • Doesn’t require light
  • e- and H+ come from NADPH as this provides energy to the e- to move across the ETC
  • This generates a H+ (proton) gradient
  • carbon fixation of RuBP produces G-3-P
  • ATP and NADPH are used to transform G3P to TP
101
Q

State the rate limiting step of photosynthesis in low and high light intensity conditions. ​

A

Rate limiting step of Photosynthesis in low-light intensity conditions:
- light

Rate limiting step of Photosynthesis in high-light intensity conditions (light is no longer a limiting factor):
- CO2 concentration or temperature

102
Q

State how plants acquire their nitrogen from nitrates

A
  • From nitrates absorbed by their roots from the soil
103
Q

What is the primary pathway for light-dependent reactions

A
  • Non-cyclic photophosphorylation
104
Q

When is non-cyclic photophosphorylation used

A

As non-cyclic photophosphorylation only produces ATP, it is an alternative pathway for when there is a greater need for ATP

105
Q

what type of reactions does photophosphorylation occur in

A

Light-dependent reactions

Biology (20 decks)

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