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MLB 111 > Unit 3 - Photosynthesis > Flashcards

Unit 3 - Photosynthesis Flashcards

1
Q

what are the 4 different types of organisms

A

determined by where the organism gets its carbon
1. autotrophs - able to convert an inorganic form of carbon into an organic form of carbon
2. photo autotrophs - get energy from sunlight, eg. plants and algae
3. chemo autotrophs - get energy from chemical compounds, eg. sulfur oxidising bacteria, nitrogen fixing bacteria and iron oxidising bacteria
4. heterotrophs - organisms that obtain their carbon from organic molecules synthesized by other organisms, eg. animals. fungi, protists, most bacteria

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2
Q

what are the equations of photosynthesis and respiration

A

Photosynthesis -
Energy + 6CO₂ + 12H₂O = C ₆H₁₂O₆ + 6O₂ +6H₂O
or Energy + Carbon dioxide + water = Glucose + Oxygen +water
(CO₂ undergoes reduction to glucose, while water undergoes oxidation to oxygen)

Respiration -
C₆H₁₂O₆ + 6O₂ = 6CO₂ +6H₂O + Energy
(glucose undergoes oxidation to carbon dioxide, while Oxygen undergoes reduction to water)

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3
Q

What are the two stages of photosynthesis

A
  1. Light dependent/Light capture
    - needs sunlight to occur
    - energy from sun is captured into usable chemical forms
  2. Light independent/Carbon fixation
    - independent of light
    - energy is used to synthesize carbohydrates from CO₂
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4
Q

why do cells need light energy

A

light energy is required for the production of NADPH and ATP, in order to further power the calvin cycle

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5
Q

what is visible light

A

the portion of electromagnetic spectrum that we can see with our eyes, which includes the range in wavelengths used in photosynthesis

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6
Q

what are pigments

A

they are molecules that absorb some wavelength of visible light - they look coloured because they reflect light enriched in the wavelengths that they don’t absorb

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7
Q

why do leaves appear green

A

because chlorophyll, the major photosynthetic pigment is poor at absorbing green wavelengths

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8
Q

What allows chlorophyll to absorb visible light

A

chlorophyll consists of a light absorbing region that contains magnesium atom at its center and a long hydrocarbon side chain. The large number of alternating double and single bonds surrounding the magnesium atom creates the overlapping electron orbitals that allow for the absorption of visible light

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9
Q

where in the chloroplast is chlorophyll found

A

it is precisely positioned with intergral membrane proteins

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10
Q

what are photosystems

A

a protein-pigment complex that absorbs light energy to drive redox reactions and thereby sets the photosynthetic electron transport chain in motion

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11
Q

what are the different forms of chlorophyll and what causes these differences

A

small differences in the chemical structure between the different types results in differences in their light absorbing properties
1. Chlorophyll a - found in all photosynthetic eukaryotes
2. Chlorophyll b - green algae and land plants

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12
Q

what are accessory pigments

A

all the light absorbing pigment other than chlorophyll in the photosynthetic membrane

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13
Q

give an eg. of a notable accessory pigment

A

carotenoids (an orange-yellow pigment) which can absorb wavelengths of visible light that are poorly absorbed by the chlorophyll

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14
Q

why are accessory pigments necessary

A

allow photosynthetic cells to absorb a broader range of wavelengths than would not be possible with chlorophyll alone

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15
Q

what is antenna chlorophyll

A

a chlorophyll molecule that absorbs energy from the sunlight and passes it to another chlorophyll molecule during photosynthesis

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16
Q

what does the antenna chlorophyll do

A
  • captures sunlight energy
  • electron in energized state
  • transfer energy to next antenna chlorophyll
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17
Q

when does this passing of energy between chlorophyll molecules stop

A

once it reaches a specially configured pair of chlorophyll molecules known as the reaction centre

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18
Q

what happens at the reaction centre

A

light energy is converted into electron transport

19
Q

what does the reaction centre do with the electron

A
  • receives energy from the antenna chlorophyll
  • transfers electron itself
    -centre becomes oxidized
  • electron acceptor is reduced
  • triggers a chain of redox reactions that ultimately leads to the formation of NADPH
20
Q

what is wrong with having an oxidized reaction centre

A

the oxidized reaction centre is unable to absorb light and cannot contribute an electron because it is missing an electron

21
Q

where does the replacement electron come from usually

A

water

22
Q

what would happen without antenna chlorophyll

A

reaction centres would sit idle much of the time, therefore working much less efficiently

23
Q

what makes water a challenging electron donor

A

it takes a great deal of energy to pull electrons from water

24
Q

what is the order in which electrons flow in the photosystems

A

from photosystem II to photosystem I

25
Q

what does the energy captured by photosystem II allow

A

allows electrons to be pulled from water, thus the energy captured by photosystem I allows electrons to be transferred to NADP+ to form NADPH

26
Q

why do electrons move in one direction between photosystems

A

the decrease in energy as they move between photosystems, running the reactions in opposite directions would require an input energy

27
Q

what are the main protein complexes of the photosynthetic electron transport chain

A

photosystem II, photosystem I, cytochrome-b6f complex (Cyt-b6f)

28
Q

how do the electrons convey between these protein complexes

A
  1. plastoquinone (Pq) diffuses through the membrane from photosystem II to Cyt-b6f
  2. Plastocyanin (Pc) diffuses through the thylakoid lumen from Cyt-b6f to Photosystem I
29
Q

where is the enzyme that pulls e- from water, and what is it released

A

located on the lumen side of the thylakoid at photosystem II
releases H+ and O2

30
Q

what does water and NADP+ do in the reaction

A

Water donates electrons to one end of the photosynthetic electron transport chain and NADP+ accepts electrons at the other end

31
Q

when is NADPH formed and where. explain the formation

A

when electrons are passed from photosystem I to ferredoxin on the stroma side of the thylakoid membrane. Ferredoxin-NADP+ reductase catalyses the formation of NADPH by transferring 2 electrons from 2 molecules of reduced Ferredoxin to NADP+ as well as a proton from the surrounding solution

32
Q

what causes protons to accumulate in the thylakoid lumen

A

the light driven movement of electrons through the photosynthetic electron transport chain

33
Q

what is photophosphorylation

A

the process by which the energy of sunlight is harnessed to move electrons, leading to the accumulation of protons and the synthesis of ATP

34
Q

what two features of the photosynthetic electron transport chain are responsible for the buildup of protons in the thylakoid lumen

A
  1. the oxidation of water, which releases protons and O2 in the thylakoid lumen
  2. Pq and Cyt-b6f, which produce a proton pump that moves protons from the stroma to the lumen
35
Q

what are three phases of the calvin cycle

A
  1. carboxylation - CO2 enters the calvin cycle and is added to RuBP, catalysed by Rubisco
  2. reduction - 3-PGA in reduced, ATP donates a phosphate group to 3-PGA and NADPH transfers two electrons plus one H+ which releases 1 phosphate group (Pi) (ATP to ADP, and NADPH to NADP+)
    this produces triose phosphates used to provide energy to cells or synthesize larger molecules
  3. regeneration - triose phosphate molecules are used to regenerate RuBP through reactions that require ATP
36
Q

Write down the calvin cycle equation

A

6CO₂ + 18ATP +12NADPH +H₂O = 16Pi + 18ADP +12 NADP+

37
Q

what compound is CO2 added to in the first phase of the calvin cycle

A

(a 5-carbon compound) ribulose 1,5-biphosphate (RuBP)w

38
Q

what catalyses phase 1 of the calvin cycle

A

Ribulose biphosphate carboxylase oxygenase (Rubisco)

39
Q

name and explain 3 photosynthetic challenges

A
  1. excess light energy can damage cells - increases chance of creating reactive molecules known as reactive oxygen species
    - formed either by the transfer of absorbed light energy from antenna chlorophyll to O2
    - or by the transfer of an electron to O2
  2. Photorespiration leads to loss of energy and carbon - Rubisco can use both CO2 and O2 as substrates
    - if O2 diffuses into the active site of rubisco instead of CO2 the reaction can still proceed, O2 is added to rubisco rather than CO2
    - results in the release of CO2 and requires light
  3. photosynthesis captures just a small % of incoming solar energy - photosynthetic electron transport chain captures about 24% of the suns energy arriving on the surface of a lea
    - the incorporation into carbohydrates results in considerable energy loss; about 20%
    - maximum energy efficiency of photosynthesis is about 4%
40
Q

Name and explain the four stages of thylakoid reaction

A
  1. Light capture -
  2. Energy transfer -
  3. Electron transport -
  4. ATP synthesis -
41
Q

Explain the different components of chloroplasts and their functions

A
  1. Lumen - third highly folded membrane that encloses a fluid filled space (photosynthetic electron transport chain is located here)
  2. Thylakoid - entire structure plus the lumen
  3. Grana - the thylakoid is folded into grana, enhances light capture due to the increased surface area
  4. Stroma - region between the inner membrane and the thylakoid membrane (carbon fixation takes place here)
42
Q

Describe the Ruben et al experiment and what it proved

A

proved that O2 released during photosynthesis was released from H2O and CO2
they found that when photosynthesizing chlorella cells were supplied with C18O₂, they did not observe heavy 18O₂ as a byproduct of photosynthesis

43
Q

what is the difference between anabolic and endergonic

A

anabolic - promotion of the synthesis of complex molecules in living organisms from simpler ones together with the storage of energy

endergonic - reactions that require a sustained input of energy

44
Q

difference between anabolism and catabolism

A

anabolism = building of complex organic molecules
catabolism = breaking of complex organic molecules

MLB 111 (4 decks)

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