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Bio 217 > Topic 8 > Flashcards

Topic 8 Flashcards

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Biology 101 flashcards
1
Q

Photosynthesis

A
  • The process that converts solar energy into chemical energy within chloroplasts
  • The process responsible for oxygen in our atmosphere
  • Important chemical process for life on earth
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2
Q
  • Autotrophs
A

“self-feeders”
* Sustain themselves without eating
anything derived from other organisms
* Producers: producing organic molecules from CO2 and other inorganic molecules
* Almost all plants are photoautotrophs
* Usetheenergyofsunlighttomake organic molecules

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3
Q

Photosynthetic Organisms

A
  • Photosynthesis occurs in plants, algae, some unicellular eukaryotes, and some prokaryotes
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4
Q
  • Heterotrophs:
A

obtain organic material from other organisms
* Consumers: eat living organisms
* Decomposers: consume dead material
* Almost all heterotrophs, including humans, depend on photoautotrophs for food and O2

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5
Q
  • Chloroplasts
A

are structurally similar to and likely evolved from photosynthetic bacteria (endosymbiont theory)
* The structural organization of chloroplasts allows for the chemical reactions of photosynthesis

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6
Q

Chloroplast Organization

A
  • Mesophyll: interior tissue of the leaf * Each mesophyll cell contains 30-40
    chloroplasts
  • Stomata: microscopic pores in leaf * Allows CO2 entry and O2 exit
  • thylakoids
  • chlorophyll
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7
Q
  • Vein:
A

delivers water from roots

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8
Q
  • Chloroplasts
A

(photosynthetic organelles)
* Mainly found in cells of the mesophyll
* Chloroplast has two membranes that surround the dense fluid known as stroma

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9
Q
  • Thylakoids:
A
  • Connected sacs in chloroplast
  • Third membrane in chloroplast
  • Site of photosynthesis (light reaction) * Thylakoid stack is known as a granum
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10
Q
  • Chlorophyll:
A
  • Pigment that gives leaves their green color
  • Resides in the thylakoid membranes
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11
Q
  • Chloroplasts are powered how
A

solar-powered chemical factories
* Thylakoidstransformlightenergyintothe chemical energy of ATP and NADPH

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12
Q
  • Wavelength
A

is the distance between crests of electromagnetic waves
* Wavelength determines thetype of electromagnetic energy
sunlight is elevtromagnetic energy

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12
Q

electromagnetic spectrum

A

the entire range of electro magnetic energy or radiation

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13
Q

visable light

A

380-750 nm
- also the wavelengths that drive photosynthesis

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14
Q

Light also behaves as

A

discrete particles called photons

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15
Q

Pigments are

A

substances that absorb visable light
- different pigments absorb different wavelengths
- wavelengths that are not absorbed are reflected or transmitted
- leaves are green bc chlorophyll reflects green light

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15
Q

A spectrophotometer measures

A

a pigment’s ability to absorb various wavelengths
* This machine sends light through pigments and measures the fraction of light transmitted at each wavelength
* An absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength

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16
Q
  • Chlorophyll a,
A

the key light-capturing pigment
* The absorption spectrum of chlorophyll a suggests that violet-blue and red light work best for photosynthesis

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17
Q

Chlorophyll b

A

an accessory pigment

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18
Q

Carotenoids

A

a separate group of accessory pigments

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19
Q

Accessory pigments,

A

, such as chlorophyll b, broaden the spectrum used for photosynthesis
* The difference in the absorption spectrum between chlorophyll a and b:
* A slight structural difference between the pigment molecules

20
Q

Accessory pigments called carotenoids may

A

broaden the spectrum of colors that drive photosynthesis
* Some carotenoids function in photoprotection
* They absorb excessive light that would damage chlorophyll or react with oxygen

21
Q

When a pigment absorbsl ight, itgoes from

A

a ground state to an excited state which is unstable
- when electrons fall back down, excess energy is released as heat
- in isolation pigments also emit light known as flourescence
-higher energy state is importnat for the light reaction

22
Q

Photosynthesis consists of the

A

Light Reactions and Calvin Cycle

23
Q
  • Light reactions vs calvin
A

photo vs synthesis

24
Q

the formula of photosynthesis

A

6 co2 + 6h20 + light energy = c6h12o6 plus 6o2

25
Q

The overall chemical change during photosynthesis is the reverse of the one that occurs

A

during cellular respiration

26
Q
  • Chloroplasts split
A

h2o into hydrogen and oxygen
- incorporates the elctrons of hydrogen into sugar molecules
- releases o2 as product

27
Q

Photosynthes isi sa

A

redox reaction in which h2o is oxidized and co2 is reduced
- endergonic process the nergy boost is provided by light

28
Q

Light Reaction Summary:

A
  • Occurs in Thylakoids
  • Split H2O
  • Release O2
  • Reduce the electron acceptor NADP+ to NADPH
  • Generate ATP from ADP by photophosphorylation
  • No production of sugar
29
Q

Light Reactions

A
  • Reduces the electron acceptor NADP+ to NADPH
  • NADPH–Nicotinamideadenine dinucleotide phosphate
  • ElectronacceptorsimilartoNADH,butwith extra phosphate group
  • Generate ATP from ADP by photophosphorylation
  • In light reactions, chemiosmosis powers addition of P to ADP
30
Q

Calvin Cycle Summary:

A
  • Occurs in the stroma
  • Forms sugar from CO2, using ATP and NADPH
  • The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules
31
Q
  • A photosystem:
A
  • A reaction-center complex surrounded
    by light-harvesting complexes
  • Photosystem II and Photosystem I in Thylakoid Membrane
32
Q

The light-harvesting complex consists of

A

pigment molecules bound to proteins
* Light-harvesting complexes transfer the energy of photons to the chlorophyll a molecules in the reaction-center complex
* These chlorophyll a molecules are special because they can transfer an excited electron to a different molecule

33
Q
  • The reaction-center complex:
A
  • Anassociationofproteinsholdingaspecialpairof chlorophyll a molecules and a primary electron acceptor
  • A primary electron acceptor in the reaction center accepts excited electrons and is reduced as a result
  • Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor > the first step of the light reactions
34
Q
  • Photosystem II (PS II)
A

functions first
* The reaction-center chlorophyll a of PS II is called P680
* Best at absorbing a wavelength of 680 nm

35
Q

Photosystem I (PS I)

A

functions second
* The reaction-center chlorophyll a of PS I is called P700
* Best at absorbing a wavelength of 700 nm

36
Q

Electron Flow in the Light Reactions

A
  • Linear electron flow:
  • The primary pathway
  • Involves both photosystems and produces ATP and NADPH using light energy
  • Eight steps in linear electron flow Figure 10.UN03
37
Q
  • Eight steps in linear electron flow
A

1) A photon of light hits a pigment in a light- harvesting complex of PS II,
* Its energy is passed among pigment molecules until it excites P680

2) An excited electron from P680 is transferred to the primary electron acceptor
* P680 is now called P680+

3) H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680
* The H+ are released into the thylakoid space
* O2 is released as a by-product of this reaction

4) Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II to PS I.
* Energyreleasedbythefalldrivesthecreationofa proton gradient across the thylakoid membrane

5) Potential energy stored in the proton gradient drives production of ATP by chemiosmosis

6) In PS I (like PS II), transferred light energy excites P700, which loses an electron to the primary electron acceptor
* P700+ accepts an electron passed down from PS II via the electron transport chain

7) Each electron “falls” down an electron transport chain from the primary electron
acceptor of PS I to the protein ferredoxin (Fd)

8) NADP+ reductase catalyzes the transfer of electrons to NADP+, reducing it to NADPH
* The electrons of NADPH are available for the reactions of the Calvin cycle
* This process also removes an H+ from the stroma (helps keep stroma at low [H+])

38
Q

Chloroplasts and mitochondria generate ATP by

A

chemiosmosis, but use different sources of energy
* Mitochondria transfer chemical energy from food to ATP
* Chloroplasts transform light energy into ATP
* Spatial organization of chemiosmosis differs, but also shows similarities

39
Q

In mitochondria:

A
  • H+ are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
40
Q

In chloroplasts:

A
  • H+ are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma
  • ATPandNADPHareproducedontheside facing the stroma, where the Calvin cycle takes place
41
Q

Moving from Light Reactions to Calvin Cycle

In summary:

A
  • Light reactions generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH
42
Q
  • The Calvin Cycle:
A
  • Is anabolic, and uses the chemical energy of ATP and
    NADPH to reduce CO2 to sugar
  • Regenerates its starting material after molecules enter and leave the cycle
  • Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3-phospate (G3P)
  • For net synthesis of one G3P, the cycle must take place three times, fixing three molecules of CO2
43
Q

The Calvin Cycle has three phases

A
  1. Carbon fixation (catalyzed by Rubisco)
  2. Reduction
  3. Regeneration of the CO2 acceptor (RuBP)
44
Q
  1. Carbon Fixation
A
  • Rubisco (RuBP carboxylase- oxygenase) enzyme
  • Mostabundantproteininchloroplasts
  • Possiblymostabundantproteinonearth
  • CO2 + a 5-C RuBP converted to short lived 6-C intermediate
  • Intermediate splits to form 3- phosphoglycerate
45
Q
  1. Reduction
A
  • Each3-phosphoglyceratereceivesphosphate group from ATP > 1,3 bisphosphoglycerate
  • Require energy input from ATP
  • ElectronsdonatedfromNADPHreduces1,3 bisphosphoglycerate to G3P (glyceraldehyde 3- phosphate)
  • Also, loss of phosphate group
  • G3Pstoresmorepotentialenergy
  • ATPandNADPHfromlightreactions
46
Q
  1. Regeneration of the CO2 acceptor, RuBP
A
  • 15C worth needs to be recycled
  • 5 molecules of G3P rearrange to form
    3 molecules of RuBP (a 5C structure)
  • Requires the energy from 3 ATP
  • Reforms 3 molecules of RuBP for next cycle
47
Q

Net Calvin Cycle

A
  • For synthesis of one G3P molecule, Calvin Cycle consumes:
  • 9 ATP
  • 6 NADPH
48
Q

Photosynthesis has two stages

A
  • Photosynthesis consists of the light reactions and Calvin cycle
  • Light reactions: photo * Calvin Cycle: synthesis

Bio 217 (14 decks)

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