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Bio 217 > Topic 8 > Flashcards

Topic 8 Flashcards

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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,

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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

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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

Study These Flashcards
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

Study These Flashcards
A

Light Reactions and Calvin Cycle

23
* Light reactions vs calvin
photo vs synthesis
24
the formula of photosynthesis
6 co2 + 6h20 + light energy = c6h12o6 plus 6o2
25
The overall chemical change during photosynthesis is the reverse of the one that occurs
during cellular respiration
26
* Chloroplasts split
h2o into hydrogen and oxygen - incorporates the elctrons of hydrogen into sugar molecules - releases o2 as product
27
Photosynthes isi sa
redox reaction in which h2o is oxidized and co2 is reduced - endergonic process the nergy boost is provided by light
28
Light Reaction Summary:
* 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
Light Reactions
* 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
Calvin Cycle Summary:
* 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
* A photosystem:
* A reaction-center complex surrounded by light-harvesting complexes * Photosystem II and Photosystem I in Thylakoid Membrane
32
The light-harvesting complex consists of
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
* The reaction-center complex:
* 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
* Photosystem II (PS II)
functions first * The reaction-center chlorophyll a of PS II is called P680 * Best at absorbing a wavelength of 680 nm
35
Photosystem I (PS I)
functions second * The reaction-center chlorophyll a of PS I is called P700 * Best at absorbing a wavelength of 700 nm
36
Electron Flow in the Light Reactions
* 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
* Eight steps in linear electron flow
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
Chloroplasts and mitochondria generate ATP by
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
In mitochondria:
* H+ are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
40
In chloroplasts:
* 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
Moving from Light Reactions to Calvin Cycle In summary:
* Light reactions generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH
42
* The Calvin Cycle:
* 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
The Calvin Cycle has three phases
1. Carbon fixation (catalyzed by Rubisco) 2. Reduction 3. Regeneration of the CO2 acceptor (RuBP)
44
1. Carbon Fixation
* 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
2. Reduction
* 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
3. Regeneration of the CO2 acceptor, RuBP
* 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
Net Calvin Cycle
* For synthesis of one G3P molecule, Calvin Cycle consumes: * 9 ATP * 6 NADPH
48
Photosynthesis has two stages
* Photosynthesis consists of the light reactions and Calvin cycle * Light reactions: photo * Calvin Cycle: synthesis

Bio 217 (14 decks)

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