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BIO112 > Unit 2 Chapter 10: Photosynthesis > Flashcards

Unit 2 Chapter 10: Photosynthesis Flashcards

1
Q

What is photosynthesis

A
  • the endergonic suite of reactions that reduces carbon dioxide to glucose(or other sugars), O2 and H2O with the help of H2O and light energy
  • consists of the light reactions which obviously depend on light and the calvin cycle which depends on the products from the light reactions
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2
Q

What do the light reactions produce

A

oxygen from H2O, ATP

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3
Q

What does the calvin cycle produce

A

sugar from CO2

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4
Q

How are the light reactions and calvin cycle linked

A

by electrons that are released when H2O splits to form O2

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5
Q

What is the electron carrier in photosynthesis

A

NADPH

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6
Q

Where does photosynthesis occur

A

chloroplasts

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7
Q

Describe the structure of chloroplasts

A

filled with vesicle-like thylakoid, which are stacked into grana, inside a thylakoid is the lumen and surrounding the thylakoids is the lumen

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8
Q

How many membranes does a chloroplast have

A

2 like the mitochondria

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9
Q

Describe chlorophylls

A

2 types: a and b

  • absorb blue and red light, reflect and transmit green light
  • give plants their green colour
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10
Q

Describe carotenoids

A
  • absorb blue and green light
  • appear yellow, orange or red
  • accessory pigments: absorb light and give energy to chlorophyll
  • Beta carotenes and xanthophylls
  • found in chloroplasts
  • extend the range of wavelengths that can drive photosynthesis
  • protect chlorophylls by accepting or stabilizing free electrons to prevent free radicals that degrade molecules
  • photosynthesis stops without these
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11
Q

What is the action spectrum

A

wavelengths that drive the light reactions

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12
Q

What are the main photosynthetic pigments

A

chlorophylls

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13
Q

What are favonoids

A
  • “natural sunscreen”
  • accessory pigment that protects plants from radiation by absorbing UV light
  • found in vacuoles
  • necessary for photosynthesis
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14
Q

What is the structure of chlorophyll a and b

A
  • both have a long isoprene tail, and a head that has a long ring with a magnesium in it where light is absorbed
  • a has a CH3, b has a CHO in the same spot
  • tail keeps the molecule in the thylakoid membrane
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15
Q

What happens when a photon of light is absorbed by chlorophyll

A

photons energy is transferred to an electron in the chlorophyll’s head, the electron gets excited and jumps to a higher energy state (only if the difference between its energy states is equal to the energy of the photon)

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16
Q

What happens if an electron simply falls back to its ground state after being excited

A

energy is released as heat and light; called florescence

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17
Q

What is the antenna complex

A

proteins and chlorophyll molecules embedded in the thylakoid membrane

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18
Q

What is resonance

A

when a red or blue photon strikes a pigment molecule in the antenna complex, energy is absorbed and electron is excited
this energy is passed to a nearby chlorophyll where another electron is then excited
-once energy is transferred og electron falls back to ground state

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19
Q

What is the reaction centre

A

complex of several proteins, pigments and other cofactors

20
Q

What occurs at the reaction centre

A

excited electrons are transferred to a specialized chlorophyll molecule that acts as an electron acceptor
-when this special chlorphyll is reduced electromag. energy is transformed into chem energy and cannot be re-emitted as fluorescence

21
Q

What are the 3 “fates” for excited electrons

A
  1. fall back to ground state and cause fluorescence (isolated pigments)
  2. induce resonance (antenna complex)
  3. transfer to an electron acceptor in a redox. reaction (reaction centre)
22
Q

Which photosystem is first and how does it work

A
  • photosystem 2 (680nm)
  • light is absorbed in antenna complex which transmits energy to reaction centre
  • pheophytin accepts excited electron from chlorophyll
  • electrons from pheophytin are passed to an ETC in the thylakoid membrane (onto PQ, onto the cytochrome complex)
  • proton gradient created which drives the synthesis of ATP
23
Q

Where is the proton gradient created in the light reactions

A

inside the thylakoid lumen

24
Q

What is the production of ATP from ADP and a phosphate group called in plants

A

photophosphorylation

25
Q

Where do the electrons that enter photosystem 2 come from and what do they do

A

H2O (splitting of water), replace the lost electron that was lost due to excitement

26
Q

How does photosystem 1 work

A
  • 700nm
  • pigments in antenna complex absorb photons and pass energy to reaction centre
  • electrons excited
  • high energy electrons pass through ETC and then to ferredoxin and then to NADP+ reductase
  • NADP+ reductase moves 2 electrons and a proton to NADP+ which reduces it to form NADPH
27
Q

How do photosystems 2 and I interact (NON-CYCLIC)

A
  • Z-scheme
    1. photons excite electrons in chlorophyll of PS2’s antenna complex
    2. energy transferred to reaction centre and P680 passes electrons to pheophytin, electrons are replaced on P680 by splitting of H2O
    3. reduced pheophytin transfers electrons to ETC where a bunch of redox rxns decrease their pot. energy
    4. using energy from the redox reactions PQ drives photons into the thylakoid lumen creating a gradient which drives ATP prod.
    5. after completing PS2’s ETC, electrons are passed to PC which picks up an electron from cytochrome complex and gives it to PS1 (replacing P700’s lost electron)
    6. then more photons hit P700 and its excited electron binds to ferredoxin which are then passed to NADP+ reductase and NADPH is produced
28
Q

What is cyclic photophosphorylation

A
  • produces only ATP
  • PS1 moves electrons back to ETC in PS2 to make ATP via photophosphorylation
  • occurs when ATP levels are low and NADPH levels are high
29
Q

Where is the site of ATP production

A

the stroma

30
Q

What is the difference between NAD and NADP

A

NADP: used for anabolic pathways
NAD: used for catabolic pathways

31
Q

What is carbon fixation

A

addition of CO2 to an org.compound

  • redox rxn where C in CO2 is reduced
  • CO2 reacts with ribulose 1,5-biphosphate (RuBP) to produce 3-phosphoglycerate (6 C molecule breaks in half to make to 3 C phosphoglycerates)
32
Q

What are the 3 steps of the calvin cycler

A
  1. carbon fixation
  2. reduction
  3. regeneration
33
Q

What is the reduction phase

A

3-phosphoglycerate is phosphorylated by ATP (6 ATP reduced to ADP) and then reduced by NADPH (6 NADPH oxidized) to make 6 G3P, (1 leaves to go make sugar, 5 others are sent to regeneration)

34
Q

What is the regeneration phase

A

3 ATPs reduced to ADP, 5 G3Ps made back into RuBP

35
Q

Where does the calvin cycle take place

A

stroma

36
Q

How many times does the calvin cycle turn

A

1 turn fixes 1 molec of CO2, 3 turns make 1 G3P

37
Q

What is the most abundant protein in the world

A

rubsico

38
Q

Which reaction starts the transformation of CO2 gas into sugars

A

reaction between CO2 and RuBP catalyzed by rubsico

39
Q

Describe rubsico

A
  • cube shaped with 8 active sites
  • slow
  • catalyzes reaction between CO2 and RuBP
  • inefficient because it catalyzes addition of O2 to RuBP as well as the addition of CO2 to RuBP
  • since O2 and CO2 have to compete, CO2 fixation is slowed
40
Q

What is photorespiration

A
  • occurs in chloroplasts
  • occurs when rubisco acts on O2 and not CO2
  • consumes energy (ATP and O2) and releases fixed CO2 “undoes photosynthesis”
  • declines photosynthesis
  • makes one 3-phosphoglycerate for calvin cycle and one 2-phosphoglycolate (the wasteful one)
41
Q

How does CO2 enter plants

A
  • stoma contains pores guarded by guard cells
  • if CO2 is low, proton pumps in guard cells establish a charge gradient so K+ ions move into guard cells; water flowing across osmotic gradient causes guard cells to swell and create a pore
42
Q

What is C3 photosynthesis

A

regular photosynthesis, RuBP +CO2 react to form two 3-phosphoglycerates (3C sugars)
-rubsico from bundle sheath cells

43
Q

What is C4 photosynthesis

A
  1. PEP carboxylase fixes CO2 in mesophyll cells makes a 4C org.acid
  2. these acids travel to bundle sheath cells via plasmodesmata
  3. the acids release a CO2 which rubisco uses to make 3-phosphogylcerate and drive the calvin cycle
  • these reactions need ATP but also increase conc. of CO2, ensuring less O2 binds to rubsico
  • used in hot dry conditions when stoma need to stay closed, and photosynthesis slows so O2 levels rise form cellular resp and photorespiration increases
44
Q

What are some examples of c4 plants

A

corn, sugar cane, crabgrass

45
Q

What is CAM photosynthesis

A
  • increases CO2 and involves 4 carbon acids
  • occurs at diff time than photosynthesis
  • at night CAM plants open their stoma and take in tons of CO2 which is fixed to the org acids and stored in vacuoles
  • during the day the molecules are process and CO2 is released for calvin cycle
  • ie, cacti
46
Q

How is photosynthesis regulated

A
  • light increases it
  • high amounts of sugar inhibit
  • rubisco activated when light is available and inhibited when theres low CO2
  • low phosphate levels stimulate calvin cycle
47
Q

What happens to sugar made from photosynthesis

A
  • 1 G3P from calvin cycle makes glucose and fructose into sucrose (cytosol)
  • alternative makes glucose into starch (chloroplast)

-slow photosynthesis makes sucrose, fast makes starch

BIO112 (19 decks)

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