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BI101 > Chapter 6- Photosynthesis > Flashcards

Chapter 6- Photosynthesis Flashcards

1
Q

What is photosynthesis

A

the use of light energy to convert carbon from CO2 gas into an organic form. Oxygen, generated from the oxidation of H2O during the process, is released as a by-product

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2
Q

What does photosynthesis provide

A

the source of all the food we eat through the direct and indirect consumption

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3
Q

autotrophs

A

Organisms that make required organic (food) molecules from inorganic sources such as CO2 and water; self-feeding

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4
Q

Heterotrophs

A

Consumers and decomposers need a source of organic (food) molecules to survive

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5
Q

Photoautotrophs

A

use light as the energy source to make organic molecules by photosynthesis

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6
Q

what are the primary produces of the earth

A

photoautotrophs

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7
Q

Photosynthetic organisms:

A
  • Convert sunlight energy into chemical energy
  • Use energy to assemble complex organic molecules from inorganic raw materials
  • The organic molecules are then used as energy sources (but also used as an energy source by other organisms)
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8
Q

what are the two stages of photosynthesis

A

light reactions and Calvin cycle

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9
Q

light reactions

A

light energy absorbed by pigment molecules is transformed into ATP and NADPH; O2 that is produced as a result of the oxidation of water is released as a by-product.

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10
Q

Calvin Cycle

A

NADPH and ATP produced during the light reactions provide energy and reducing power to fix carbon from CO2 and convert it into carbohydrates

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11
Q

what type of reaction is photosynthesis

A

redox reaction

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12
Q

where does photosynthesis take place

A

In eukaryotes (higher plants, algae), photosynthesis takes place in chloroplasts

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13
Q

Chloroplast Structure

A

Surrounded by two membranes: outer and inner membranes
Separated by intermembrane space

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14
Q

Thylakoid membranes
- location
- structure

A

Location of photosynthetic pigments and electron transport chain
A complex of flattened, closed sacs
Stacks of membranes called grana

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15
Q

thylakoid lumen

A

The soluble compartment enclosed by thylakoids

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16
Q

Photosynthesis impacts global CO2 levels

A

You can see CO2 levels increase during the late fall and through the winter in the northern hemisphere, and decrease starting in the spring and through the summer

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17
Q

The Sun converts matter to energy, releasing it as

A

electromagnetic energy

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18
Q

The range of wavelengths of electromagnetic radiation is called the

A

electromagnetic spectrum

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19
Q

what is light

A

light is defined as the portion of the electromagnetic spectrum that humans can detect with their eyes

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20
Q

what does light behave as

A

Light behaves like a wave and like particles of energy (photons), and thus can be understood as a wave of photons.

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21
Q

Electromagnetic spectrum

A

forms radiant energy that differ in wavelength (horizontal distance between crests of successive waves)

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22
Q

Visible light has wavelengths between about

A

700 nm (red light) and 400 nm (blue light)
- we see the entire spectrum combined together as white light

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23
Q

the amount of energy in a unit of light is ______ proportional to wavelength

A

inversely proportional
- the shorter the wavelength, the greater the energy of the photon

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24
Q

When photons of light hit an object, 1 of 3 things can happen. The photon can be:

A
  • reflected
  • transmitted
  • absorbed
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25
Q

to use energy light must be

A

absorbed - the energy of a photon must be transferred to an electron within the molecule
- switched the electronfrom a grounded state tp an excited state

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26
Q

pigments

A

molecules that absorb photons of specific wavelengths

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27
Q

Critical light absorption feature:

A

a region where carbon atoms are covalently bonded to each other with alternating single and double bonds (conjugated system)

28
Q

A pigment’s colour is the result of

A

photons of light it does not absorb

29
Q

what is a major photosynthetic pigment

A

chlorophyll

30
Q

why does each type of pigment absorb light of only certain wavelengths

A
  • differences in arrangement of conjugated systems
  • different chemical structures
31
Q

Three Fates of an Excited-State Electron

A
  1. Excited electron returns to its ground state, releasing energy as heat or as the light of a longer wavelength (fluorescence)
  2. Energy from the excited electron in one pigment molecule is transferred to a neighbouring pigment molecule
    * Transfer excites the second pigment, returning the first pigment to its ground state
  3. Excited-state electron itself is transferred to a nearby electron-accepting molecule
32
Q

what are accessory pigments

A

Chlorophyll b and carotenoids
- they donate excited energy to chlorophyll a via inductive resonance

33
Q

what drives the reaction of photosyntheiss

A

light absorbed by chlorophylls and carotenoids acting in combination

34
Q

whats a pigments absorption spectrum

A

The amount of light of different wavelengths that is absorbed by a pigment

35
Q

what is the action spectrum of photosynthesis

A

The effectiveness of light of each wavelength in driving photosynthesis produces a graph

36
Q

what did Theodor Engelmann do

A

used a glass prism to break light into a spectrum of colours—cast across a microscope slide with a strand of algae and aerobic bacteria.
* Bacteria grew best where algae released oxygen in greatest quantity —in areas of blue, violet, and red light.
* Engelmann constructed an action spectrum for wavelengths of light, showing the effects of each colour on photosynthesis

37
Q

Antenna complex

A
  • absorbs light energy (chlorophyll a/b, carotenoids)
  • energy transferred to reaction center chlorophyll a molecules via inductive resonance
38
Q

Reaction centre

A

pair of special chlorophyll a molecules of the reaction center is bound by proteins
- P680 PSII
- P700 PSI

39
Q

Photosystems I and II

A
  • Photosystems composed of many pigments and proteins
  • Special chlorophyll a molecules in the reaction centers can be oxidized (photoreduction)
40
Q

Photosystem II

A

Special chlorophyll a molecules in the reaction center are called P680
- P = pigment; 680 denotes wavelength of max absorbance for the reaction center

41
Q

Photosystem I

A

Specialized chlorophyll a molecules in the reaction centre called P700 molecules

42
Q

what are the photosystem connected by

A

photosynthetic electron transport

43
Q

Photosystem II

A
  • e- in P680 raised from ground state to excited state P680*
  • P680* oxidized to P680+ by primary e- acceptor Pheophytin (Pheo)
  • Pheo transfers e- to PQ
    * Shuttles e- to cytochrome complex
  • P680 is reformed when P680+ gains an e- from oxidation of H2O
    * Water splitting complex
44
Q

Photosynthetic Electron Transport and ATP Synthesis

A
  • Electrons released by the oxidation of the reaction center chlorophylls of photosystem II (P680) are passed along an electron transport chain

This photosynthetic electron transport chain (the light reactions) uses energy of light absorbed by photosystem II and photosystem I to generate reducing power in the form of NADPH (high energy electron carrier), and forms a H+ gradient that can be used to generate ATP.

45
Q

Linear Electron Transport 1: Oxidation of P680 in Photosystem II

A

Absorption of light by PS II results in formation of P680*
* P680* gets oxidized to P680+ by the primary e- acceptor Pheophytin (Pheo)

46
Q

Linear Electron Transport 2 Oxidation-reduction of Plastoquinone Pool

A
  • The Electron given up by chlorophyll to Pheo is transferred to plastoquinone (PQ); the electron “hole” in P680 chlorophyll is replaced by the oxidation of water
  • PQ also takes a H+ from stroma, migrates through lipid bilayer
  • Donates e- to cytochrome b6/f complex
  • Releases H+ into lumen
47
Q

Linear Electron Transport 3 Electron transfer from cytochrome complex to PC

A
  • The cytochrome complex transfers electrons to plastocyanin (PC)
  • PC shuttles e- to Photosystem I
48
Q

Linear Electron Transport 4 Oxidation-Reduction of P700 in PS I

A
  • Absorption of light by PS I results in formation of P700*
  • Oxidation of P700* to P700+ by the primary e- acceptor of PS I
  • e- “hole” in P700+ chlorophyll is replaced by e- donated by PC
49
Q

Linear Electron Transport 5 Electron Transfer to NADP+ by Ferredoxin

A
  • e- from PSI is transferred to ferredoxin (iron-sulfur protein)
  • e- transferred to NADP+ (Final e- acceptor) via Ferredoxin
  • NADP+ gets reduced to NADPH by NADP+ reductase
50
Q

Chemiosmotic Synthesis of ATP

A
  • Proton-motive force established across thylakoid membrane used to synthesize ATP by chemiosmosis and ATP Synthase
    * H+ flow from thylakoid lumen into stroma drives synthesis of ATP
51
Q

Energy levels on the thylakoid membrane

A
  • absorption of light energy by PS II allows electrons pulled from the water to enter the photosynthetic ETC
  • a second input if light energy by PS I produces electron donor molecules capable of reducing NADP+
52
Q

how many photons of light to get 1 electron through the electron transport chain from photosystem II to NADP+

A

takes 2 photons of light (i.e. 1 photon absorbed by each photosystem)

53
Q

Photosystem I can operate independently of photosystem II by using

A

the cyclic electron transport
- keeps moving protons across the thylakoid membrane without involvement of photosystem II

54
Q

cyclic electron transport

A
  • reduced ferredoxin can donate electrons back to the plastoquinone pool, which gets continually reduced and oxidized
    -Energy absorbed from light is therefore converted into chemical energy of ATP but not NADPH as a result of cyclic electron transport
55
Q

what does the Calvin cycle require more of ATP or NADH

A

ATP

56
Q

Calvin cycle

A

metabolic pathway that reduces CO2 and converts it into organic substances. It is an anabolic, endergonic process. NADPH provides electrons and hydrogen ATP provides additional energy

57
Q

Carbon fixation

A

involves capturing CO2 molecules with the key enzyme Rubisco (RuBP carboxylase/oxygenase)

58
Q

what is the most abundant protein on earth

A

Rubisco

59
Q

rubisco and oxygen activity

A

O2 acts as a competitive inhibitor of Rubisco’s carboxylase activity

60
Q

what does Rusbisco have a larger affinity for CO2 or O2

A

co2

61
Q

Terrestrial plants, especially those in hot dry climates, face problems of

A

Photorespiration and water loss

62
Q

what is a leas surface covered with to prevent water loss

A

waxy cuticle- but also prevents rapid diffusion of gases into leaf

63
Q

what regulates gas exchange

A

stomata

64
Q

Dilemma of plants in hot dry climates:

A

Need to open stomata to let in CO2, but need to keep them closed to conserve water

65
Q

Some plants have evolved the C4 pathway to

A

increase the concentration of CO2 relative to O2 near Rubisco so that photorespiration is minimized

66
Q

C4 cycle

A

CO2 is combined with a 3-carbon molecule, phosphoenolpyruvate (PEP), to produce a 4- carbon intermediate

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