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Biology HL IB 2020-22 > 8.3 Photosynthesis (HL) > Flashcards

8.3 Photosynthesis (HL) Flashcards

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1
Q

Chloroplast: How many membranes?

A
  1. Inner and outer membrane
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2
Q

Chloroplast: What is the stroma?

A

Similar to the cytoplasm, it surrounds the thylakoids

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3
Q

Chloroplast: What is the stroma involved in?

A
  • Involved in light independent reactions of the cell like Calvin’s cycle, carbon fixation
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4
Q

Chloroplast: What do thylakoid membranes and granum look like in microscope?

A

Shows as darker or thicker green clumps

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5
Q

Chloroplast: Function of thylakoid and grana

A

Offer large surface area where light-dependent reactions occur like photolysis. Photosystems, ATP synthase are embedded

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6
Q

Chloroplast: Function of thylakoid intermembrane space

A

Small volume allows fast generation of H+ ion gradient for chemiosmosis

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7
Q

Chloroplast: What does stroma contain?

A

Rubisco, enzymes, substrates, NADPH, molecules for Calvin cycle

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8
Q

Chloroplast: 70S ribosomes

A

Synthesize some of the proteins and enzymes needed within the chloroplast

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9
Q

Chloroplast: Naked DNA

A

Codes for some for the chloroplast proteins

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10
Q

Purpose and mitochondrial equivalent: Chloroplast envelope

A
  • Membranes which compartmentalize organelles in cytoplasm

- Outer mitochondrial membrane

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11
Q

Purpose and mitochondrial equivalent: Thylakoid membrane

A
  • Carries out ETC, has ATP synthase, makes use of chemiosmosis
  • Inner mitochondrial membrane
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12
Q

Purpose and mitochondrial equivalent: Grana

A
  • Maximize surface area for reactions

- Cristae

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13
Q

Purpose and mitochondrial equivalent: Low volume intermembrane space

A
  • Rapid generation of H+ conc. gradient

- Low volume intermembrane space

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14
Q

Purpose and mitochondrial equivalent: Stroma

A
  • Fluid medium for diffusion of molecules and enzymes for reactions
  • Matrix (But instead for Krebs cycle)
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15
Q

Light-dependent reactions: Steps

A
  • Photoactivation
  • Photolysis
  • ETC
  • Chemiosmosis
  • ATP synthesis
  • NADP reduction
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16
Q

Photoactivation and photolysis: What is a photosystem?

A

A collection of chlorophyll molecules and other accessory pigments that combine with a protein

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17
Q

Photoactivation and photolysis: Which photosystem is activated first?

A

PSII

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18
Q

Photoactivation and photolysis: Difference between PSI and PSII

A

PSI is sensitive to wavelengths of 700nm while PS2 to wavelengths of 680nm

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19
Q

Photoactivation and photolysis: Function of PSII

A

Absorbs the light energy, splits water and gathers electrons from photolysis

20
Q

Photoactivation and photolysis: What is a reaction center?

A

A collection of proteins and pigments wherein pigments transfer all the energy from light photons to a central chlorophyll a molecule

21
Q

Photoactivation and photolysis: Summary of process in PSII

A
  • 2 excited electrons are passed to primary electron acceptor which passes it to plastoquinone and then PSI
  • PSII will repeat so 4 electrons are lost in one cycle
  • Water is split as reaction becomes powerful oxidizing agent
22
Q

Photoactivation and photolysis: Why can the electrons be used in light-dependent reactions again?

A
  • They constantly replace electrons lost by PSII

- Electrons lost from the reaction center are replaced by electrons derived from water

23
Q

ETC: Summary of process/photophosphorylation

A
  • Excited electrons from PSII are transferred to thylakoid membrane
  • Electrons lose energy passing through chain so H+ ions accumulate in thylakoid
  • This creates EC gradient
  • Protons return to stroma via ATP synthase in transmembrane
  • ATP synthase catalyzes synthesis of ATP
  • De-energized electrons are taken to PSI
24
Q

What receives the electrons from PSI?

A

Ferredoxin

25
Q

What does ferredoxin do?

A

It reduces NADP+ which is carried to light-independent reactions

26
Q

What does the NADP molecule accept?

A

2 electrons from PSI and 2 H+ ions from stroma

27
Q

What happens in cyclic phosphorylation?

A
  • Involves use of one PS and no reduction of NADP+ or splitting of water. - - Excited electron enters ETC and comes back to same PS to restore electron supply
28
Q

What happens in non-cyclic phosphorylation?

A
  • Involves 2 PS and reduction NADP+
  • Light is absorbed by PSII and excited electron enters ETC
  • Photoactivation results in release of electrons for NADP+ and photolysis of water replaces those lost
29
Q

Why is cyclic used?

A

Can be used to produce a steady supply of ATP in presence of sunlight for cell energy demands

30
Q

Why is cyclic not ideal?

A

ATP is highly reactive and so it cannot be readily stored in the cell

31
Q

Why is non-cyclic the preferred phosphorylation?

A
  • Both NADPH and ATP are required to produce organic molecules via light independent reactions
  • Only non-cyclic allows for synthesis of organic molecules and long-term energy storage
32
Q

Is oxygen evolved in cyclic and non-cyclic?

A

Oxygen is only evolved in non-cyclic

33
Q

Light independent: What are the 3 steps?

A
  1. Carbon fixation
  2. Carboxylation of ribulose biphosphate (RuBP)
  3. Triose phosphate production (Form organic molecules or reform stocks of RuBP)
34
Q

Light independent: Where does it take place?

A

In the stroma of the chloroplast

35
Q

Light independent: Can they occur without absence of light?

A

Only for a short while as they stop when stock of NADPH and ATP runs out

36
Q

Light independent: 1st step- What is carbon fixation? Which enzyme is used?

A

Atmospheric CO2 is fixed by adding RuBP. It is catalyzed by rubisco. RuBP is carboxylated to form a hexose biphosphate compound
- Results in breakdown into molecules of PGA

37
Q

Light independent: What is RuBP?

A

5 carbon molecule

38
Q

Light independent: 2nd step- Reduction of 3-PGA (What is 3PGA)

A
  • 3-PGA consists of 3 C atoms and it stands for glycerate 3-phosphate
  • It is reduced to triose phosphate which also has 3 C atoms by ATP and NADPH
39
Q

Light independent: Release of triose phosphate (3rd step)

A

Only 1 molecule is released and it is used for carb synthesis

40
Q

Light independent: Regeneration of RuBP (4th step)

A
  • 6 triose phosphates are produced per cycle but since it’s 3C, one glucose monomer is made through 2 cycles.
  • Remaining 5 TP molecules are recombined to regenerate RuBP
  • Regeneration requires energy from hydrolysis of ATP
41
Q

Why are light-independent reactions costly?

A
  • One molecule of triose phosphate requires 3 turns of the Calvin cycle which uses 3 ATP and 2 NADPH per cycle
    > 3C + 3C from RuBP = hexose + 2C
    > 2C + 4C from RuBP= Hexose + 1C
    > 1C + 5C from RuBP = hexose
42
Q

Calvin’s lollipop experiment: Which element was used and why?

A

Carbon-14, a radioactive isotope because he argued that if CO2 was starting material, radioactive products would appear from the organism (like Chlorella)

43
Q

Calvin’s lollipop experiment: What apparatus was used and why?

A

Used the lollipop apparatus to control when the carbon was added to the green algal liquid

44
Q

Calvin’s lollipop experiment: Summary of process

A
  • Drained samples at certain intervals and let it drop into boiling ethanol, stopping the reaction
  • Samples were used in chromatography
  • Chromatograms were exposed to X-ray films to make radiograms that capture position of products during photosynthesis
  • Analyzed products to deduce pathway of Calvin cycle
45
Q

Calvin’s lollipop experiment: What did he find?

A
  • Large amount of 3-PGA was found after 5 seconds

- After 30s, PGA, PEPA, triose phosphate were showing high percentage of radioactivity

Biology HL IB 2020-22 (24 decks)

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